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+![ITU logo: A globe with a red lightning bolt and the letters ITU.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: A globe with a red lightning bolt and the letters ITU.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**P.1010**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+(07/2004)
+
+SERIES P: TELEPHONE TRANSMISSION QUALITY,  
+TELEPHONE INSTALLATIONS, LOCAL LINE  
+NETWORKS
+
+Transmission performance and QoS aspects of IP end-points
+
+---
+
+**Fundamental voice transmission objectives for  
+VoIP terminals and gateways**
+
+ITU-T Recommendation P.1010
+
+---
+
+# ITU-T P-SERIES RECOMMENDATIONS
+
+## TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS
+
+|                                                                                               |               |               |
+|-----------------------------------------------------------------------------------------------|---------------|---------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality | Series        | P.10          |
+| Subscribers' lines and sets                                                                   | Series        | P.30<br>P.300 |
+| Transmission standards                                                                        | Series        | P.40          |
+| Objective measuring apparatus                                                                 | Series        | P.50<br>P.500 |
+| Objective electro-acoustical measurements                                                     | Series        | P.60          |
+| Measurements related to speech loudness                                                       | Series        | P.70          |
+| Methods for objective and subjective assessment of quality                                    | Series        | P.80<br>P.800 |
+| Audiovisual quality in multimedia services                                                    | Series        | P.900         |
+| <b>Transmission performance and QoS aspects of IP end-points</b>                              | <b>Series</b> | <b>P.1000</b> |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# **ITU-T Recommendation P.1010**
+
+# **Fundamental voice transmission objectives for VoIP terminals and gateways**
+
+## **Summary**
+
+This Recommendation provides 3.1 kHz telephony speech transmission performance requirements for the whole range of packet-based gateways and terminals, including wireless and softphones. Measurement methodologies are not covered by this Recommendation, however, work on this topic is under way in Study Group 12 and is planned to be incorporated in a future revision or, alternatively, in a separate new Recommendation. Also, requirements for wideband telephony may be added in a future version of this Recommendation.
+
+###### **Source**
+
+ITU-T Recommendation P.1010 was approved on 7 July 2004 by ITU-T Study Group 12 (2001-2004) under the ITU-T Recommendation A.8 procedure.
+
+# FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
+
+© ITU 2004
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+# CONTENTS
+
+|                                                                        | Page |
+|------------------------------------------------------------------------|------|
+| Scope .....                                                            | 1    |
+| 1 Introduction .....                                                   | 1    |
+| 2 References.....                                                      | 1    |
+| 3 Terms and definitions .....                                          | 2    |
+| 4 Abbreviations and acronyms .....                                     | 3    |
+| 5 End-to-end considerations .....                                      | 3    |
+| 6 Transmission characteristics.....                                    | 3    |
+| 6.1 Default coding algorithm.....                                      | 4    |
+| 6.2 Delay.....                                                         | 4    |
+| 6.3 Send Loudness Rating .....                                         | 5    |
+| 6.4 Receive Loudness Rating .....                                      | 5    |
+| 6.5 Weighted Terminal Coupling Loss (TCLw) .....                       | 6    |
+| 6.6 Residual Echo Level.....                                           | 6    |
+| 6.7 Further parameters with respect to speech processing devices ..... | 6    |
+| 7 Measurement considerations .....                                     | 6    |
+
+
+
+# Fundamental voice transmission objectives for VoIP terminals and gateways
+
+## Scope
+
+This Recommendation provides fundamental speech transmission performance requirements for 3.1 kHz handset telephony of packet-based terminals and gateways; it applies to both access gateways and trunking gateways. Requirements are given for handset operation, with the assumption that the corresponding requirements for headset and handsfree are obtained via appropriate conversions to take into account the different acoustic reference points.
+
+This Recommendation addresses the whole range of IP-based gateways and terminals, including wireless and softphones.
+
+Measurement methodologies are not covered by this Recommendation; however, work on this topic is under way in Study Group 12 and is planned to be incorporated in a future revision or alternatively in a separate new Recommendation.
+
+# 1 Introduction
+
+This Recommendation limits its scope to the fundamental speech transmission performance requirements for VoIP terminals and VoIP gateways with respect to the interface with the packet-based network. Thus, a number of traditional parameters have not been considered in this Recommendation. This is mainly because it is anticipated that the respective requirements from existing Recommendations, e.g., P.310 [11] or in the Q.55x series of Recommendations, can be applied to VoIP terminals and VoIP gateways in an appropriate way. Attention should also be paid to the end-to-end considerations provided in clause 5.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [1] ITU-T Recommendation G.100 (2001), *Definitions used in Recommendations on general characteristics of international telephone connections and circuits*.
+- [2] ITU-T Recommendation G.107 (2003), *The E-model, a computational model for use in transmission planning*.
+- [3] ITU-T Recommendation G.108 (1999), *Application of the E-model: A planning guide, plus Amendment 1 (2003): New Appendix I – The relationship between and interaction of talker echo and absolute delay, and Amendment 2 (2004): New Appendix II – Planning examples regarding delay in packet-based networks*.
+- [4] ITU-T Recommendation G.108.2 (2003), *Transmission planning aspects of echo cancellers*.
+- [5] ITU-T Recommendation G.109 (1999), *Definition of categories of speech transmission quality*.
+
+- [6] ITU-T Recommendation G.168 (2004), *Digital network echo cancellers*.
+- [7] ITU-T Recommendation G.711 (1988), *Pulse code modulation (PCM) of voice frequencies*.
+- [8] ITU-T Recommendation G.799.1/Y.1451.1 (2004), *Functionality and interface specifications for GSTN transport network equipment for interconnecting GSTN and IP networks*.
+- [9] ITU-T Recommendation G.1020 (2003), *Performance parameter definitions for quality of speech and other voiceband applications utilizing IP network*, plus Amendment 1.
+- [10] ITU-T Recommendation P.10 (1998), *Vocabulary of terms on telephone transmission quality and telephone sets*, plus Amendment 1 (2003): *New Annex A – List of psychoacoustic parameters*.
+- [11] ITU-T Recommendation P.310 (2003), *Transmission characteristics for telephone band (300-3400 Hz) digital telephones*.
+- [12] ITU-T Recommendation P.330 (2003), *Speech processing devices for acoustic enhancement*.
+- [13] ITU-T Recommendation P.340 (2000), *Transmission characteristics and speech quality parameters of hands-free terminals*.
+- [14] ITU-T Recommendation P.380 (2003), *Electro-acoustic measurements on headsets*.
+- [15] ITU-T Recommendation P.501 (2000), *Test signals for use in telephonometry*.
+- [16] ITU-T Recommendation P.502 (2000), *Objective test methods for speech communication systems using complex test signals*.
+- [17] ITU-T Recommendation Q.115.1 (2002), *Logic for the control of echo control devices and functions*.
+- [18] ITU-T Recommendation Y.1541 (2002), *Network performance objectives for IP-based services*.
+- [19] ANSI/TIA/EIA-810-A (2000), *Transmission Requirements for Narrowband Voice over IP and Voice over PCM Digital Wireline Telephones*.
+
+# 3 Terms and definitions
+
+Beside those in ITU-T Recs P.10 [10] and G.100 [1] this Recommendation defines the following terms:
+
+**3.1 send loudness rating (SLR):**  $SLR = SLR(\text{set}) + \sum_{i=1}^n CLR_i$
+
+**3.2 receive loudness rating (RLR):**  $RLR = RLR(\text{set}) + \sum_{i=n+1}^N CLR_i$
+
+**3.3 overall loudness rating (OLR):**  $OLR = SLR + RLR$
+
+**3.4 circuit loudness rating (CLR):** The loudness loss between two electrical interfaces in a connection or circuit.
+
+**3.5 softphone:** A softphone is an implementation of a VoIP terminal which is realized by a software program enabling a personal computer (PC) or personal digital assistant (PDA) equipped with an acoustic interface (microphone and earpiece/loudspeaker) to be used for two-way voice communications.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations:
+
+|          |                                 |
+|----------|---------------------------------|
+| CLR      | Circuit Loudness Rating         |
+| IP       | Internet Protocol               |
+| IPDV     | IP Packet Delay Variation       |
+| OLR      | Overall Loudness Rating         |
+| RLR      | Receive Loudness Rating         |
+| RLR(set) | RLR of a telephone set          |
+| SCN      | Switched-Circuit Network        |
+| SLR      | Send Loudness Rating            |
+| SLR(set) | SLR of a telephone set          |
+| T        | Mean One-Way Delay              |
+| TCLw     | Weighted Terminal Coupling Loss |
+| UNI      | User-Network Interface          |
+| VAD      | Voice Activity Detection        |
+| VoIP     | Voice over Internet Protocol    |
+
+# 5 End-to-end considerations
+
+In order to achieve a desired end-to-end speech transmission performance (mouth-to-ear) it is recommended that transmission planning tasks be carried out with the E-model of ITU-T Rec. G.107 [2] as described in ITU-T Rec. G.108 [3]; this includes the *a priori* determination of the desired category of speech transmission quality as defined in ITU-T Rec. G.109 [5].
+
+While, in general, the transmission characteristics of single circuit-oriented network elements, such as switches or terminals, can be assumed to have a single input value for the planning tasks of ITU-T Rec. G.108 [3], this approach is not applicable in packet-based systems and, thus, there is a need for the transmission planner's specific attention.
+
+In particular, the decision as to which delay category given in this Recommendation should be chosen to represent the specific configuration is the responsibility of the individual transmission planner.
+
+ITU-T Rec. G.108 with its Amendments [3] provides further guidance on this important issue.
+
+# 6 Transmission characteristics
+
+The requirements specified in this clause apply to both VoIP terminals and VoIP gateways with respect to the interface with the packet-based network as illustrated in Figure 1.
+
+![Figure 1/P.1010 – Area of applicability of this Recommendation. The diagram shows two parallel horizontal signal paths. Top path: A VoIP terminal (represented by a box with a handset icon) connects to a box labeled 'path through IP network(s)'. Between them is a dot labeled 'UNI'. Another 'UNI' dot is at the output of the network path. A double-headed arrow spans the VoIP terminal. Bottom path: A box labeled 'SCN' connects to a 'VoIP gateway' box, which then connects to a 'path through IP network(s)' box. 'UNI' dots are placed between the gateway and network, and at the network output. A double-headed arrow spans the VoIP gateway. The label 'P1010_F1' is in the bottom right.](a5ee5c23b6dc52ec1d724b76d5a5f58f_img.jpg)
+
+Figure 1/P.1010 – Area of applicability of this Recommendation. The diagram shows two parallel horizontal signal paths. Top path: A VoIP terminal (represented by a box with a handset icon) connects to a box labeled 'path through IP network(s)'. Between them is a dot labeled 'UNI'. Another 'UNI' dot is at the output of the network path. A double-headed arrow spans the VoIP terminal. Bottom path: A box labeled 'SCN' connects to a 'VoIP gateway' box, which then connects to a 'path through IP network(s)' box. 'UNI' dots are placed between the gateway and network, and at the network output. A double-headed arrow spans the VoIP gateway. The label 'P1010\_F1' is in the bottom right.
+
+**Figure 1/P.1010 – Area of applicability of this Recommendation**
+
+## 6.1 Default coding algorithm
+
+VoIP terminals and VoIP gateways shall support the coding algorithm according to ITU-T Rec. G.711 [7] (both  $\mu$ -law and A-law). VoIP terminals and VoIP gateways may support other coding algorithms.
+
+## 6.2 Delay
+
+While delay incurred from traditional terminals was significantly lower than the delay possibly incurred from the network, this is no longer true for VoIP terminals and for VoIP gateways.
+
+Hence, for traditional terminals, the appropriate Recommendations (e.g., ITU-T Rec. P.310) were able to specify one single requirement for delay.
+
+With the introduction of packet-based transmission, however, the increased delays introduced by the terminals and the gateways can have a tremendous impact on the end-to-end delay and, thus, need proper consideration in transmission planning. For example, depending on the delay variation accumulated by packets traversing an IP network, the design of the de-jitter buffer of an IP gateway or terminal is extremely critical and has to consider a trade-off between the permissible number of dropped packets and the maximum delay to be incurred (see Figure 3/G.1020 [9]).
+
+Accordingly, for the parameter of delay, IP terminals and gateways may be designed to operate in a number of modes, with the mode selection being based on end-to-end considerations, especially desired speech quality level and likely network configurations.
+
+For IP networks which comply with or which perform better than Class 0 of ITU-T Rec. Y.1541 [18], terminals or gateways that comply with any of the three delay categories given in this Recommendation will be a starting point to achieve acceptable speech quality.
+
+For other kinds of networks, for example, networks with larger delay variations than any class of Y.1541 limits, only delay categories A or B may be a valid choice. Furthermore, there are cases such as the interconnection of two local IP islands via an intercontinental path through the PSTN, where only delay category A will be a valid basis for achieving a reasonable end-to-end speech transmission performance (due to the long delay of the PSTN path).
+
+Irrespective of network configurations encountered, the deployment of some low bit rate codecs may further decrease the perceived speech quality and narrow the valid choice of delay categories.
+
+The following subclauses specify three delay categories for either send or receive directions. It is the common understanding that, in order to comply with a specific delay category, a VoIP terminal or a VoIP gateway has to comply with both send and receive requirements of this category.
+
+NOTE – For some VoIP terminals, e.g., softphones, it is well recognized that, under certain circumstances, technical and practical considerations may not permit any of the above categories to be met at this time. Therefore, this issue, as well as the introduction of a fourth delay category, are for further study.
+
+### 6.2.1 Send delay categories (provisional values)
+
+For a VoIP terminal, send delay is defined as the one-way delay from the acoustical input (mouthpiece) of this VoIP terminal to its interface to the packet-based network. VoIP gateway send delay is defined as the one-way delay from the electrical input (TDM or analogue) of this VoIP gateway to the interface to the packet-based network. In each case, the total send delay is the upper bound on the mean delay and takes into account the delay contributions of all of the elements shown in Figures 2 and A.1/G.1020 [9], respectively.
+
+- Category A:  $T_s \leq 20$  ms;
+- Category B:  $T_s \leq 35$  ms;
+- Category C:  $T_s \leq 50$  ms.
+
+### 6.2.2 Receive delay categories (provisional values)
+
+For a VoIP terminal, receive delay is defined as the one-way delay from the interface to the packet-based network of this VoIP terminal to its acoustical output (earpiece). VoIP gateway receive delay is defined as the one-way delay from the interface to the packet-based network to the electrical output (TDM or analogue) of this VoIP gateway. In each case, the total receive delay is the upper bound on the mean delay and takes into account the delay contributions of all of the elements shown in Figures 3 and A.2/G.1020 [9], respectively.
+
+- Category A:  $T_r \leq 30$  ms;
+- Category B:  $T_r \leq 65$  ms;
+- Category C:  $T_r \leq 100$  ms.
+
+#### 6.2.2.1 IP Packet delay variation (IPDV)
+
+VoIP terminals and gateways should accommodate network IPDV values of up to 50 ms; this is consistent with ITU-T Rec. Y.1541 Classes 0 and 1. It is left to the designer's discretion whether the VoIP terminal or gateway is capable of accommodation of IPDV values above this value, which may occur in other networks.
+
+## 6.3 Send Loudness Rating
+
+For VoIP terminals, the recommended nominal value of Send Loudness Rating (SLR) should be:
+
+- $SLR = SLR(set) = 8$  dB.
+
+For VoIP gateways, the recommended nominal value of Send Loudness Rating (SLR) should be:
+
+- $SLR = SLR(set) + CLR = 8$  dB.
+
+For the gateway at the ingress to the IP network, the nominal SLR has to be achieved solely by means of transmission planning; this requires a proper dimensioning of the CLR.
+
+## 6.4 Receive Loudness Rating
+
+For VoIP terminals, the recommended nominal value of Receive Loudness Rating (RLR) should be:
+
+- $RLR = RLR(set) = 2$  dB.
+
+For VoIP gateways, the recommended nominal value of Receive Loudness Rating (RLR) should be:
+
+- $RLR = RLR(set) + CLR = 2$  dB.
+
+For the gateway at the egress from the IP network, the nominal RLR has to be achieved solely by means of transmission planning; this requires a proper dimensioning of the CLR.
+
+## 6.5 Weighted Terminal Coupling Loss (TCLw)
+
+Due to the increased delay values introduced by VoIP terminals compared to traditional digital terminals as per ITU-T Rec. P.310 [11], the TCLw requirement needs to be increased (see also ANSI/TIA/EIA-810-A [19]).
+
+For VoIP terminals the recommended nominal value of weighted Terminal Coupling Loss (TCLw) should be:
+
+- $TCLw \geq 55$  dB
+
+For further details see clause 10/P.310 [11]; in addition, the TCLw has to be maintained under all operational conditions. Relaxation of the TCLw value by not more than 10 dB is only permissible during double-talk periods. Note that this value is provisional and for further study.
+
+NOTE – TCLw is strongly influenced by the amount of acoustic coupling in the acoustic interface. In the absence of any standardized requirements for this interface, the recommended value of TCLw may not always be met. Nevertheless, in the interest of achieving satisfactory speech quality, designers of VoIP terminals should strive to meet this value as closely as possible, taking into account the characteristics of the acoustic interfaces to be used.
+
+## 6.6 Residual Echo Level
+
+For VoIP gateways, an echo canceller according to ITU-T Rec. G.168 [6], is recommended for cancelling echoes that may originate in the PSTN. For details regarding control of Echo Cancellers see Annex A/Q.115.1 [17]. Details on the residual echo level that may be achieved and on transmission planning aspects for echo cancelling devices, are discussed in ITU-T Rec. G.108.2 [4]. Details on functional aspects of trunking gateways can be found in ITU-T Rec. G.799.1/Y.1451.1 [8].
+
+## 6.7 Further parameters with respect to speech processing devices
+
+For VoIP terminals and gateways that contain non-linear speech processing devices, the following parameters require additional attention and are for further study in the context of this Recommendation:
+
+- objective evaluation of speech quality for VoIP gateways and VoIP terminals;
+- double-talk capability;
+- switching behaviour;
+- partial echo effects;
+- occurrence of artefacts;
+- time-variant impairments.
+
+As is the case for traditional telephone sets, reduced performance for handsfree and headset mode operation is anticipated for VoIP terminals. Further guidance in this area is provided by ITU-T Recs P.340 [13] and P.380 [14].
+
+# 7 Measurement considerations
+
+Measurement methodologies are not covered by this Recommendation; however, work on this topic is under way in Study Group 12 and is planned to be included in a future revision or, alternatively, in a separate new Recommendation.
+
+Nevertheless, it can be assumed that VoIP terminals and gateways contain non-linear and time-variant functions (e.g., automatic gain control, adaptive jitter buffer, VAD). This needs to be considered when approaching the measurement of transmission characteristics. ITU-T Recs P.330 [12], P.501 [15] and P.502 [16] provide further guidance in this respect.
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                |
+|-----------------|--------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                              |
+| Series B        | Means of expression: definitions, symbols, classification                                                                      |
+| Series C        | General telecommunication statistics                                                                                           |
+| Series D        | General tariff principles                                                                                                      |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                              |
+| Series F        | Non-telephone telecommunication services                                                                                       |
+| Series G        | Transmission systems and media, digital systems and networks                                                                   |
+| Series H        | Audiovisual and multimedia systems                                                                                             |
+| Series I        | Integrated services digital network                                                                                            |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                    |
+| Series K        | Protection against interference                                                                                                |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant                                        |
+| Series M        | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                |
+| Series O        | Specifications of measuring equipment                                                                                          |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                            |
+| Series Q        | Switching and signalling                                                                                                       |
+| Series R        | Telegraph transmission                                                                                                         |
+| Series S        | Telegraph services terminal equipment                                                                                          |
+| Series T        | Terminals for telematic services                                                                                               |
+| Series U        | Telegraph switching                                                                                                            |
+| Series V        | Data communication over the telephone network                                                                                  |
+| Series X        | Data networks and open system communications                                                                                   |
+| Series Y        | Global information infrastructure, Internet protocol aspects and Next Generation Networks                                      |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                           |

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+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.1203.1**
+
+(01/2019)
+
+SERIES P: TELEPHONE TRANSMISSION QUALITY,  
+TELEPHONE INSTALLATIONS, LOCAL LINE  
+NETWORKS
+
+Models and tools for quality assessment of streamed  
+media
+
+---
+
+**Parametric bitstream-based quality assessment  
+of progressive download and adaptive  
+audiovisual streaming services over reliable  
+transport – Video quality estimation module**
+
+Recommendation ITU-T P.1203.1
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a stylized globe with a red lightning bolt striking through it, symbolizing global communication and technology.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+# ITU-T P-SERIES RECOMMENDATIONS
+
+## TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS
+
+|                                                                                                    |               |               |
+|----------------------------------------------------------------------------------------------------|---------------|---------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality      | Series        | P.10          |
+| Voice terminal characteristics                                                                     | Series        | P.30          |
+|                                                                                                    |               | P.300         |
+| Reference systems                                                                                  | Series        | P.40          |
+| Objective measuring apparatus                                                                      | Series        | P.50          |
+|                                                                                                    |               | P.500         |
+| Objective electro-acoustical measurements                                                          | Series        | P.60          |
+| Measurements related to speech loudness                                                            | Series        | P.70          |
+| Methods for objective and subjective assessment of speech quality                                  | Series        | P.80          |
+| Methods for objective and subjective assessment of speech and video quality                        | Series        | P.800         |
+| Audiovisual quality in multimedia services                                                         | Series        | P.900         |
+| Transmission performance and QoS aspects of IP end-points                                          | Series        | P.1000        |
+| Communications involving vehicles                                                                  | Series        | P.1100        |
+| <b>Models and tools for quality assessment of streamed media</b>                                   | <b>Series</b> | <b>P.1200</b> |
+| Telemeeting assessment                                                                             | Series        | P.1300        |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                  | Series        | P.1400        |
+| Methods for objective and subjective assessment of quality of services other than speech and video | Series        | P.1500        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T P.1203.1
+
+## Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Video quality estimation module
+
+## Summary
+
+Recommendation ITU-T P.1203.1 specifies the short-term video representation quality estimation modules for ITU-T P.1203 (Pv module). The ITU-T P.1203-series of Recommendations specifies modules for a set of model algorithms for monitoring the integral media session quality for transport control protocol (TCP) type video streaming. The models comprise modules for short-term video-quality (described in this part of the Recommendation family) and audio-quality estimation. The per-one-second outputs of these short-term modules are integrated into estimates of audio-visual quality and together with information about initial loading delay and media playout stalling events, they are further integrated into the final model output, to provide an estimate of integral quality. The respective ITU-T work item has formerly been referred to as "Parametric non-intrusive assessment of TCP-based multimedia streaming quality", or "P.NATS". The ITU-T P.1203.1 part of ITU-T P.1203 provides details for the modules for bitstream-based, short-term video quality estimation.
+
+Four different modes can be used for the Pv module specified in this Recommendation. These modes – referred to as mode 0 to 3 – use input information of differing complexity and amount and represent four model algorithms each with a different level of complexity. The Pv modules comprise components reflecting the effects due to video compression, up-scaling of content and the effect due to low frame rates. The four different modes use the same overall model architecture and individual coefficients and all have the same components for up-scaling and framerate. The only Pv module component that differs between modes is the Pv module component related to video compression.
+
+This revision to Recommendation ITU-T P.1203.1 (2017) replaces the scale factor defined in clause 8.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T P.1203.1 | 2016-12-22 | 12          | <a href="http://handle.itu.int/11.1002/1000/13159">11.1002/1000/13159</a> |
+| 2.0     | ITU-T P.1203.1 | 2017-10-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/13400">11.1002/1000/13400</a> |
+| 3.0     | ITU-T P.1203.1 | 2019-01-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/13845">11.1002/1000/13845</a> |
+
+## Keywords
+
+Adaptive streaming, audio, audiovisual, IPTV, mean opinion score (MOS), mobile TV, mobile video, monitoring, multimedia, progressive download, QoE, TV, video.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2019
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+###### Page
+
+|     |                                                                   |    |
+|-----|-------------------------------------------------------------------|----|
+| 1   | Scope.....                                                        | 1  |
+| 2   | References.....                                                   | 3  |
+| 3   | Definitions .....                                                 | 4  |
+| 3.1 | Terms defined elsewhere .....                                     | 4  |
+| 3.2 | Terms defined in this Recommendation.....                         | 4  |
+| 4   | Abbreviations and acronyms .....                                  | 4  |
+| 5   | Conventions .....                                                 | 4  |
+| 6   | Pv module in ITU-T P.1203 context.....                            | 4  |
+| 6.1 | Pv module modes .....                                             | 5  |
+| 7   | Model input.....                                                  | 5  |
+| 7.1 | I.13 input specification .....                                    | 6  |
+| 8   | Model algorithm and output .....                                  | 6  |
+| 8.1 | Core model .....                                                  | 7  |
+|     | Annex A – Mode 0 Pv module: <i>quant</i> description.....         | 10 |
+| A.1 | Performance analysis.....                                         | 11 |
+|     | Annex B – Mode 1 Pv module: <i>Dq</i> description .....           | 12 |
+| B.1 | <i>quant</i> calculation .....                                    | 12 |
+| B.2 | <i>Dq</i> calculation for mode 1 .....                            | 13 |
+| B.3 | Performance analysis.....                                         | 14 |
+|     | Annex C – Mode 2 Pv module: <i>quant</i> description.....         | 15 |
+| C.1 | Consideration on parameter extraction.....                        | 15 |
+| C.2 | <i>quant</i> calculation .....                                    | 17 |
+| C.3 | Performance analysis.....                                         | 17 |
+|     | Annex D – Mode 3 Pv module: <i>quant</i> description.....         | 18 |
+| D.1 | Performance analysis.....                                         | 19 |
+|     | Annex E – <i>MOSfromR</i> and <i>RfromMOS</i> and functions ..... | 20 |
+| E.1 | <i>MOSfromR</i> definition .....                                  | 20 |
+| E.2 | <i>RfromMOS</i> definition .....                                  | 20 |
+|     | Annex F – Byte-counting algorithm for Mode 2 .....                | 22 |
+
+
+
+## **Recommendation ITU-T P.1203.1**
+
+## **Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Video quality estimation module**
+
+# **1 Scope**
+
+This Recommendation describes the video module as an integral part of the ITU-T P.1203-series Recommendations. The ITU-T P.1203 Recommendations describe a set of objective parametric quality assessment modules. Combined, these modules can be used to predict the impact of audio and video media encodings as well as Internet protocol (IP) network impairments on the quality experienced by an end-user of multi-media streaming applications.
+
+The addressed streaming techniques comprise progressive download as well as adaptive streaming, for both mobile and fixed network streaming applications over transport control protocol (TCP) or other TCP like protocols which are not affected by transmission errors.
+
+The model described is restricted to information provided to it by an appropriate packet- or bitstream-analysis module. The overall ITU-T P.1203 model is applicable for the effects due to audio- and video-coding as well as initial loading delay or stalling (which are both caused by rebuffering at the client) as the typical degradations associated with progressive download. As final output, the ITU-T P.1203-series models target integral audiovisual media quality scores.
+
+This Recommendation describes four different quality modules, one for each mode of ITU-T P.1203, that is, modes 0, 1, 2 and 3. The video quality module predicts mean opinion scores (MOS) on a 5-point ACR scale (see [ITU-T P.910]) as a per-one-second MOS score. The underlying measurement window is described in [ITU-T P.1203]. If used stand-alone, the video module can provide estimates of short-term video quality at per-one-second intervals.
+
+This model cannot provide a comprehensive evaluation of video transmission quality as perceived by an individual end user because its scores reflect the impairments due to video scaling, framerate and coding only. Furthermore, the scores predicted by a parametric model necessarily reflect an average perceptual impairment.
+
+Note also that the model was developed and validated for one specific encoder and decoder implementation. If a different encoder and decoder pair is used in a monitoring situation the scores may not reflect that.
+
+Effects such as flicker due to low source bitrate or other, not coding or transmission caused impairments related to the payload are not reflected in the scores computed by this model. Moreover, the scores predicted by a parametric model (especially in case of no access to payload or pixel information) necessarily reflect a somewhat simplified representation of the perceptual impairment of the considered stream.
+
+However, the model still enables estimation of some coding quality related information and thus valid and in most cases accurate predictions, presuming that it is applied in an appropriate manner, following this Recommendation.
+
+Table 1-1 shows application areas, test factors and coding technologies where ITU-T P.1203.1 for adaptive streaming and progressive download has been verified and is known to produce reliable results.
+
+**Table 1-1 – Application areas, test factors and coding technologies where ITU-T P.1203.1 for adaptive streaming and progressive download has been verified and is known to produce reliable results**
+
+| <b>Applications for which the model is intended</b>                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| In-service monitoring of TCP- video. Both so called over-the-top (OTT) services (for example YouTube) and operator managed video services (over TCP), using the protocols HTTP/TCP/IP and RTMP/TCP/IP. Note that this model is agnostic to the type of container format (Flash (FLV), MP4, WebM and 3GP). |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+| Performance and quality assessment of live networks (including codecs) considering the effect due to encoding bitrate, encoding resolution, and encoding framerate.                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+| <b>Video test factors for which the model has been validated</b>                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
+| Video content                                                                                                                                                                                                                                                                                             | Movie trailers, sports videos, documentaries, freely available HD content, time lapse videos, etc.                                                                                                                                                                                                                                                                                                                                                                                                                                |
+| Input video length                                                                                                                                                                                                                                                                                        | Maximum 20 seconds. The video model produces a per-second score considering input data from a measurement window of max. 20 s length.                                                                                                                                                                                                                                                                                                                                                                                             |
+| Bitstream container                                                                                                                                                                                                                                                                                       | Elementary stream contained in MPEG-2 transport stream (TS) segments                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
+| Encoder/decoder implementation                                                                                                                                                                                                                                                                            | <p>The model has been trained using the following video encoder/decoder:</p> <ul style="list-style-type: none"> <li>– ITU-T H.264/MPEG-4 AVC High profile: x264 (ffmpeg)</li> <li>– A common framework was developed based on the above codec, all the test data was generated using the common framework.</li> </ul> <p>It is assumed that the model can be used for estimating quality when other encoder implementations for the given codec have been used. However, model performance cannot be guaranteed in this case.</p> |
+| Slice size                                                                                                                                                                                                                                                                                                | 1 slice per video frame                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
+| Scene-cut detection                                                                                                                                                                                                                                                                                       | Off                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
+| x264 Preset                                                                                                                                                                                                                                                                                               | Medium                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
+| Video resolution/bitrate                                                                                                                                                                                                                                                                                  | <p>240p: 75-150 kbit/s</p> <p>360p: 220-450 kbit/s</p> <p>480p: 375-750 kbit/s</p> <p>720p: 1 050-2 100 kbit/s</p> <p>1080p: 1 875-12 500 kbit/s</p> <p>Note that aspect ratio of 16:9 is maintained for all quality levels.</p>                                                                                                                                                                                                                                                                                                  |
+| Group of pictures (GOP)                                                                                                                                                                                                                                                                                   | 1 second length, IBBBP only                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
+| Segment length                                                                                                                                                                                                                                                                                            | <p>1-9 seconds</p> <p>NOTE – The segment length determines how often the quality can be adapted.</p>                                                                                                                                                                                                                                                                                                                                                                                                                              |
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T G.107] Recommendation ITU-T G.107 (2015), *The E-model: a computational model for use in transmission planning*.
+- [ITU-T H.264] Recommendation ITU-T H.264 (2016), *Advanced video coding for generic audiovisual services*.
+- [ITU-T P.800.1] Recommendation ITU-T P.800.1 (2006), *Mean opinion score (MOS) terminology*.
+- [ITU-T P.910] Recommendation ITU-T P.910 (2008), *Subjective video quality assessment methods for multimedia applications*.
+- [ITU-T P.911] Recommendation ITU-T P.911 (1998), *Subjective audiovisual quality assessment methods for multimedia applications*.
+- [ITU-T P.1201.1] Recommendation ITU-T P.1201.1 (2012), *Parametric non-intrusive assessment of audiovisual media streaming quality – Lower resolution application area*.
+- [ITU-T P.1201.2] Recommendation ITU-T P.1201.2 (2012), *Parametric non-intrusive assessment of audiovisual media streaming quality – Higher resolution application area*.
+- [ITU-T P.1202] Recommendation ITU-T P.1202 (2012), *Parametric non-intrusive bitstream assessment of video media streaming quality*.
+- [ITU-T P.1202.1] Recommendation ITU-T P.1202.1 (2012), *Parametric non-intrusive bitstream assessment of video media streaming quality – Lower resolution application area*.
+- [ITU-T P.1203] Recommendation ITU-T P.1203 (2016), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport*.
+- [ITU-T P.1203.2] Recommendation ITU-T P.1203.2 (2016), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Audio quality estimation module*.
+- [ITU-T P.1203.3] Recommendation ITU-T P.1203.3 (2016), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Quality integration module*.
+- [ITU-T P.1401] Recommendation ITU-T P.1401 (2012), *Methods, metrics and procedures for statistical evaluation, qualification and comparison of objective quality prediction models*.
+
+# **3 Definitions**
+
+## **3.1 Terms defined elsewhere**
+
+This Recommendation uses the following term defined elsewhere:
+
+### **3.1.1 mean opinion score (MOS): [ITU-T P.800.1]**
+
+Further terms are defined in [ITU-T P.1203].
+
+## **3.2 Terms defined in this Recommendation**
+
+None.
+
+# **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                                      |
+|------|--------------------------------------|
+| AAC  | Advanced Audio Coding                |
+| DASH | Dynamic Adaptive Streaming over HTTP |
+| FEC  | Forward Error Correction             |
+| GOP  | Group Of Pictures                    |
+| HD   | High Definition (television)         |
+| IP   | Internet Protocol                    |
+| MOS  | Mean Opinion Score                   |
+| MPEG | Moving Pictures Expert Group         |
+| OTT  | Over The Top                         |
+| RBSP | Raw Byte Sequence Payload            |
+| SD   | Standard Definition                  |
+| TS   | Transport Stream                     |
+| TCP  | Transport Control Protocol           |
+| UDP  | User Datagram Protocol               |
+
+# **5 Conventions**
+
+None.
+
+# **6 Pv module in ITU-T P.1203 context**
+
+The overall model structure is shown in Figure 6-1, highlighting the position of the Pv module. More details on the general structure can be found in [ITU-T P.1203].
+
+![Figure 6-1: Pv module in context of building blocks of the ITU-T P.1203 model. The diagram shows a flow from 'Stream I.01' through 'Media parameter extraction' (I.11) and 'Buffer parameter extraction' (I.14) to 'Input information'. 'I. GEN: Device info available to all modules' feeds into the 'Pv: Video quality estimation module (ITU-T P.1203.1)' (I.13) and 'Pa: Audio quality estimation module (ITU-T P.1203.2)'. Both modules feed into 'Diagnostic information', which includes 'Pq: Quality integration module (ITU-T P.1203.3)', 'Pav: A/V integration/temporal', and 'Pb: quality impact due to buffering'. The final output is 'Integral MOS' (0.46).](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+The diagram illustrates the architecture of the ITU-T P.1203 model. A stream labeled 'Stream I.01' enters from the left. It is processed by two extraction blocks: 'Media parameter extraction' (output I.11) and 'Buffer parameter extraction' (output I.14). These outputs are grouped under 'Input information'. A box labeled 'I. GEN: Device info available to all modules' provides input to both the 'Pv: Video quality estimation module (ITU-T P.1203.1)' (receiving I.13) and the 'Pa: Audio quality estimation module (ITU-T P.1203.2)' (receiving I.11). Both modules output to a 'Diagnostic information' block. This block contains the 'Pq: Quality integration module (ITU-T P.1203.3)', which further contains 'Pav: A/V integration/temporal' and 'Pb: quality impact due to buffering'. The outputs from these sub-modules (0.34, 0.35, and 0.23) are combined into the final 'Integral MOS' of 0.46. A reference label 'P.1203.1(17)\_F6-1' is at the bottom right.
+
+Figure 6-1: Pv module in context of building blocks of the ITU-T P.1203 model. The diagram shows a flow from 'Stream I.01' through 'Media parameter extraction' (I.11) and 'Buffer parameter extraction' (I.14) to 'Input information'. 'I. GEN: Device info available to all modules' feeds into the 'Pv: Video quality estimation module (ITU-T P.1203.1)' (I.13) and 'Pa: Audio quality estimation module (ITU-T P.1203.2)'. Both modules feed into 'Diagnostic information', which includes 'Pq: Quality integration module (ITU-T P.1203.3)', 'Pav: A/V integration/temporal', and 'Pb: quality impact due to buffering'. The final output is 'Integral MOS' (0.46).
+
+**Figure 6-1 – Pv module in context of building blocks of the ITU-T P.1203 model**
+
+## 6.1 Pv module modes
+
+The modes of operation for ITU-T P.1203.1 are defined in Table 6-1. Detailed information on exactly which inputs are available for each mode is provided in Table 7-1. Individual models are specified per mode and are described in Annexes A, B, C, D.
+
+**Table 6-1 – ITU-T P.1203.1 modes of operation**
+
+| Mode | Encryption                                      | Input                                               | Complexity |
+|------|-------------------------------------------------|-----------------------------------------------------|------------|
+| 0    | Encrypted media payload and media frame headers | Meta-data                                           | Low        |
+| 1    | Encrypted media payload                         | Meta-data and frame header information              | Low        |
+| 2    | No encryption                                   | Meta-data and up-to 2% of the media stream          | Medium     |
+| 3    | No encryption                                   | Meta-data and any information from the video stream | Unlimited  |
+
+# 7 Model input
+
+The model receives media information and prior knowledge about the media stream. In various modes of operation, inputs may be extracted or estimated from network transmissions in different ways, which are outside the scope of this Recommendation but which may be added in future annexes. The core video quality model receives the following input signals regardless of the mode of operation, following the measurement window-based procedure as specified in [ITU-T P.1203], clause 7.4:
+
+I.13: video coding information, as specified in [ITU-T P.1203], clause 7.1.
+
+Note that fault correction techniques, such as automatic repeat request (ARQ) and forward error correction (FEC) used for user datagram protocol (UDP) based streaming are not applicable in this case, where the streaming is TCP based. In TCP-based transport all retransmissions and packet loss information is typically handled transparently by the transport layer and while it can be available to
+
+the models described in this Recommendation it is not needed. The only information provided to the model that may implicitly include effects such as packet loss and respective retransmission is the initial loading delay and stalling information provided to the quality integration module (see [ITU-T P.1203.3]).
+
+## 7.1 I.13 input specification
+
+Table 7-1 specifies the inputs to the module. Note that the actual information available to the module at a specific output sample timestamp is restricted by the measurement window as defined in [ITU-T P.1203], clause 7.4.
+
+**Table 7-1 – Description of I.13**
+
+| ID          | Description                  | Values                                                                   | Frequency         | Modes |
+|-------------|------------------------------|--------------------------------------------------------------------------|-------------------|-------|
+| <b>I.13</b> |                              |                                                                          |                   |       |
+| 12          | Target video bit-rate        | Bit-rate in kbit/s                                                       | Per media segment | All   |
+| 13          | Video frame-rate             | Frame rate in frames per second                                          | Per media segment | All   |
+| 14          | Segment duration             | Duration in seconds                                                      | Per media segment | All   |
+| 15          | Video encoding resolution    | Number of pixels (WxH) in transmitted video                              | Per media segment | All   |
+| 16          | Video codec and profile      | One of: H264-baseline, H264-high, H264-main                              | Per media segment | All   |
+| 17          | Video frame number           | Integer, starting at 1, denoting frame sequence number in encoding order | Per video frame   | 1,2,3 |
+| 18          | Video frame duration         | Duration of the frame in seconds                                         | Per video frame   | 1,2,3 |
+| 19          | Frame presentation timestamp | The frame presentation timestamp                                         | Per video frame   | 1,2,3 |
+| 20          | Frame decoding timestamp     | The frame decoding timestamp                                             | Per video frame   | 1,2,3 |
+| 21          | Video frame size             | The size of the encoded video frame in bytes                             | Per video frame   | 1,2,3 |
+| 22          | Type of each picture         | "I" or "Non-I" for mode 1                                                | Per video frame   | 1     |
+| 23          | Video bitstream              | Encoded video bytes for the frame                                        | Per video frame   | 2,3   |
+
+# 8 Model algorithm and output
+
+The video module defined in this Recommendation has one output, O.22. It provides output values on the 5-point ACR scale ("MOS") per output sampling interval.
+
+There is a core model algorithm, which is described hereafter. It comprises four different modes, which all are based on the same basic function. For all four modes, the degradation due to spatial up-scaling of content that is streamed at lower resolution as well as the handling of temporal/jerkiness-related degradations due to low video framerates are the same. Only a third degradation term addressing video compression artefacts, referred to as  $D_q$  in clause 8.1.1, is mode-dependent.
+
+The core model as well as the terms that are mode-independent are described in this clause. The model component addressing coding-related degradations, the "quantization-related component" that depends on the respective mode, is given in Annexes A (mode 0) through D (mode 3).
+
+The following parameters are used in the description of the model:
+
+- *quant*, *quant*  $\in [0,1]$ : a parameter capturing the quantization degradation; its computation depends on the variant of the quantization degradation module.
+- *scaleFactor*, *scaleFactor*  $\in [1, \infty]$ : a parameter capturing the upscaling degradation.
+- *framerate*: the video frame rate in frames per second.
+- *disRes*: the video display resolution in number of pixels. For instance, high definition (HD) 1080p screens have a video display resolution of  $disRes = 1920 \times 1080 = 2073600$  pixels.
+- *codRes*: the video encoding resolution in pixels. The video resolution used to encode the video, for instance,  $codRes = 854 \times 480 = 409920$  pixels.
+- *displaySize*: the video display diagonal length, in cm or inches.
+- *deviceType*: a parameter describing how the device is used; if the video display is handheld/mobile or stationary, such as a PC or TV. This parameter is preferably set based on knowledge about the device but can also be estimated from the *displaySize* parameter if it is unknown. In the case of unknown device, *deviceType* must be set to "handheld" if *displaySize* is smaller than 33 cm (13"). If in the same scenario it is equal to or larger than 33 cm, *deviceType* is "TV".
+
+## 8.1 Core model
+
+Figure 8-1 shows the Pv module in the context of building blocks of the ITU-T P.1203 model.
+
+### 8.1.1 Quantization degradation
+
+$$Dq = 100 - R_{fromMOS}(\widehat{MOSq}) \quad (1)$$
+
+where *R<sub>fromMOS</sub>* is described in Annex E (as in [ITU-T G.107]), and
+
+$$Dq = \max(\min(Dq, 100), 0)$$
+
+and where:
+
+$$\widehat{MOSq} = q_1 + q_2 \cdot \exp(q_3 \cdot quant) \quad (2)$$
+
+and
+
+$$\widehat{MOSq} = \max(\min(\widehat{MOSq}, 5), 1)$$
+
+with  $q_1 = 4.66$ ,  $q_2 = -0.07$  and  $q_3 = 4.06$ .
+
+![Diagram of the Pv module showing three input blocks (Quantization, Temporal, Upscaling) feeding into an Integration module. The Quantization module takes 'quant' as input and outputs 'Dq'. The Temporal module takes 'framerate' as input and outputs 'Dt'. The Upscaling module takes 'disRes' and 'codRes' as inputs and outputs 'Du'. All three outputs (Dq, Dt, Du) are fed into the Integration module (Block 400), which outputs the final 'MOS' value. The diagram is labeled P.1203.1(17)_F8-1.](5dfc130b129ace4df375839020a5700d_img.jpg)
+
+The diagram illustrates the Pv module's architecture. It consists of three parallel processing blocks on the left that feed into a single integration block on the right. 
+ 
+
+- Block 100 (Quantization module):** Takes the parameter *quant* as input and produces the degradation metric *Dq*.
+- Block 300 (Temporal module):** Takes the *framerate* parameter as input and produces the degradation metric *Dt*.
+- Block 200 (Upscaling module):** Takes the parameters *disRes* and *codRes* as inputs and produces the degradation metric *Du*.
+
+ The metrics *Dq*, *Dt*, and *Du* are then fed into **Block 400 (Integration module)**, which outputs the final Mean Opinion Score (*MOS*). The diagram is labeled P.1203.1(17)\_F8-1.
+
+Diagram of the Pv module showing three input blocks (Quantization, Temporal, Upscaling) feeding into an Integration module. The Quantization module takes 'quant' as input and outputs 'Dq'. The Temporal module takes 'framerate' as input and outputs 'Dt'. The Upscaling module takes 'disRes' and 'codRes' as inputs and outputs 'Du'. All three outputs (Dq, Dt, Du) are fed into the Integration module (Block 400), which outputs the final 'MOS' value. The diagram is labeled P.1203.1(17)\_F8-1.
+
+Figure 8-1 – Pv module in the context of building blocks of the ITU-T P.1203 model
+
+### 8.1.2 Upscaling degradation
+
+$$Du = u_1 \cdot \log_{10}(u_2 \cdot (\text{scaleFactor} - 1) + 1) \quad (3)$$
+
+with
+
+$$Du = \max(\min(Du, 100), 0)$$
+
+and
+
+$$\text{scaleFactor} = \max\left(\frac{\text{disRes}}{\text{codRes}}, 1\right) \quad (4)$$
+
+with  $u_1 = 72.61$  and  $u_2 = 0.32$ .
+
+### 8.1.3 Temporal degradation
+
+$$D_t = \begin{cases} D_{t1} - D_{t2} - D_{t3}, & \text{framerate} < 24 \\ 0, & \text{framerate} \geq 24 \end{cases} \quad (5)$$
+
+Pure temporal degradation:
+
+$$D_{t1} = \frac{100 \cdot (t_1 - t_2 \cdot \text{framerate})}{t_3 + \text{framerate}} \quad (6)$$
+
+Compensation variable 1, relative to coding impact:
+
+$$D_{t2} = \frac{D_q \cdot (t_1 - t_2 \cdot \text{framerate})}{t_3 + \text{framerate}} \quad (7)$$
+
+Compensation variable 2, relative to spatial scaling impact:
+
+$$D_{t3} = \frac{Du \cdot (t_1 - t_2 \cdot \text{framerate})}{t_3 + \text{framerate}} \quad (8)$$
+
+$$D_t = \max(\min(D_t, 100), 0)$$
+
+where  $t_1 = 30.98$ ,  $t_2 = 1.29$  and  $t_3 = 64.65$ .
+
+### 8.1.4 Integration
+
+Degradation ( $D$ ) is calculated based on the quantization ( $D_q$ ), upscaling ( $D_u$ ) and temporal ( $D_t$ ) degradations as follows:
+
+$$D = \max(\min(D_q + D_u + D_t, 100), 0) \quad (9)$$
+
+Maximum quality according to the pure upscaling and temporal degradations is calculated as follows:
+
+$$\widehat{Qmax} = \begin{cases} 100 - D_u - D_{t1}, & \text{framerate} < 24 \\ 100 - D_u, & \text{framerate} \geq 24 \end{cases} \quad (10)$$
+
+Then, quality ( $Q$ ) is calculated as follows:
+
+$$\begin{aligned} \widehat{Q} &= 100 - D = \\ &\begin{cases} 100 - \max\left(\min\left((100 - \widehat{Qmax}) + D_q - D_{t2} - D_{t3}, 100\right), 0\right), & \text{framerate} < 24 \\ 100 - \max\left(\min\left((100 - \widehat{Qmax}) + D_q, 100\right), 0\right), & \text{framerate} \geq 24 \end{cases} \end{aligned} \quad (11)$$
+
+Finally,
+
+$$\widehat{MOS} = MOSfromR(\widehat{Q}) \quad (12)$$
+
+where  $\widehat{Q}$  is the estimated video encoding, with  $\widehat{Q} \in [0, 100]$ .
+
+*MOSfromR* is described in Annex E.
+
+$D$  is the overall degradation due to video representation (spatial and temporal sampling, video compression).
+
+If deviceType is "handheld", the following adjustment must be made on the final score:
+
+$$\begin{aligned}\widehat{MOS}_{handheld} &= htv1 + htv2 \cdot \widehat{MOS} + htv3 \cdot \widehat{MOS}^2 + htv4 \cdot \widehat{MOS}^3 \\ \widehat{MOS} &= \max(\min(\widehat{MOS}_{handheld}, 5), 1)\end{aligned}\quad (13)$$
+
+The four coefficients in the TV/handheld-adjustment are:
+
+| Coefficient | Value    |
+|-------------|----------|
+| <i>htv1</i> | -0.60293 |
+| <i>htv2</i> | 2.12382  |
+| <i>htv3</i> | -0.36936 |
+| <i>htv4</i> | 0.03409  |
+
+It is noted that higher *D*, *Dq*, *Du* and *Dt* values mean higher degradations and therefore lower quality. Higher  $\widehat{Q}$  and  $\widehat{MOS}$  values mean higher quality.
+
+In the following Annexes A through D, different variants of the quant parameter are described, one for each of the four modes.
+
+The initial output delivered addresses the case of presentation on a PC screen of 1920x1080 pixel resolution. To estimate the O.22 output delivered by the video quality estimation module Pv for the case of viewing on a mobile device, the following adjustment of the output score is proposed.
+
+# Annex A
+
+## Mode 0 Pv module: *quant* description
+
+(This annex forms an integral part of this Recommendation.)
+
+In the case of mode 0, *quant* is calculated as described in Equation (A.2):
+
+$$quant = a_1 + a_2 \cdot \ln(a_3 + \ln(br) + \ln(br \cdot bpp + a_4)) \quad (A.1)$$
+
+and *bpp* is the number of kbits per pixel:
+
+$$bpp = \frac{br}{codRes \cdot fr} \quad (A.2)$$
+
+where:
+
+*fr* : framerate in frames per second
+
+*codRes* : coding resolution in number of pixels of the frame
+
+*br* : video stream bitrate in kbit/s.
+
+In case of TS-segments, the bitrate can be estimated using information about the chunk size, setting
+
+$$br = brChunkSize \quad (A.3)$$
+
+*brChunkSize* : estimated encoding video bitrate in kbit/s, computed from the chunk size as follows:
+
+$$brChunkSize = \frac{chunkSize \cdot 8 - audioSize - tsHeader - pesHeader}{videoDur \cdot 1000} \quad (A.4)$$
+
+where:
+
+*chunkSize* : chunk (audio + video) size in Bytes
+
+*videoDur* : duration of the video chunk in seconds
+
+and where:
+
+$$tsHeader = 4 \cdot 8 \cdot \frac{chunkSize}{188} \quad (A.5)$$
+
+and
+
+$$pesHeader = 17 \cdot 8 \cdot (numVideoFrames + numAudioFrames) \quad (A.6)$$
+
+where:
+
+*numVideoFrames* : number of video frames in the chunk
+
+*numAudioFrames* : number of video and audio frames in the chunk.
+
+*numVideoFrames* and *numAudioFrames* are computed as follows:
+
+$$numVideoFrames = int(ceil(videoDur \cdot framerate)) \quad (A.7)$$
+
+and
+
+$$numAudioFrames = int(ceil(audioDur \cdot \frac{audioSampleRate}{samplesPerFrame})) \quad (A.8)$$
+
+where:
+
+*audioSampleRate* : audio sample rate in Hz, e.g., 48 000
+
+*samplesPerFrame* : number of samples per audio frame, e.g., 1024 for AAC
+
+*audioDur* : audio duration within the chunk in seconds.
+
+Further:
+
+$$audioSize = audioBrTarget \cdot audioDur \cdot 1000 \quad (\text{A.9})$$
+
+where:
+
+*audioBrTarget*: targeted encoding audio bitrate in kbit/s
+
+If other means of determining the video stream bitrate are available, these may be used instead of the above calculation approach, which uses the chunk sizes.
+
+Table A.1 shows coefficient sets for *quant* parameter calculation for mode 0.
+
+**Table A.1 – Coefficient sets for *quant* parameter calculation for Mode 0**
+
+| Coefficient | Value    |
+|-------------|----------|
+| $a_1$       | 11.99835 |
+| $a_2$       | -2.99992 |
+| $a_3$       | 41.24751 |
+| $a_4$       | 0.13183  |
+
+## A.1 Performance analysis
+
+See [ITU-T P.1203] for details on the performance of the complete model with the mode 0 Pv module.
+
+# Annex B
+
+## Mode 1 Pv module: *Dq* description
+
+(This annex forms an integral part of this Recommendation.)
+
+For mode 1, the *Dq* estimation for mode 0, that is, the estimation of the degradation due to coding, is amended by a frame-information-dependent term that addresses the complexity of the video content. This way, the prediction is improved over mode 0, by considering how contents with different degrees of complexity lead to a modified encoding effectiveness.
+
+As shown in the equations below, the modification is carried out outside of the mode 0 *Dq*-calculation and not made part of the *quant* parameter. As a consequence, Annex B describes the calculation of the complete *Dq* for this case, instead of only the calculation of the *quant* parameter. This is in contrast to the modes 0, 2 and 3, where all effects covered by the respective module instantiation are captured by *quant* directly.
+
+### B.1 *quant* calculation
+
+In the case of mode 1, *quant* is calculated as described in Equation (B.4) for mode 2, but with different coefficient values than in the case of mode 0 (see Annex A):
+
+$$quant = a_1 + a_2 \cdot \ln(a_3 + \ln(br) + \ln(br \cdot bpp)) \quad (B.1)$$
+
+and *bpp* is the number of kbits per pixel:
+
+$$bpp = \frac{brFrameSize}{codRes \cdot fr} \quad (B.2)$$
+
+where:
+
+*fr* : framerate in frames per second  
+*br* *FrameSize*.
+
+Here, *bpp* is calculated based on the parameter *brFrameSize*, the video bitrate in kbit/s computed from the video frame sizes.
+
+*brFramesize* is computed as:
+
+$$brFramesize = \frac{\sum_{index=1}^{numVideoFrames} frameSizes(index) \cdot 8}{frameDuration \cdot numVideoFrames \cdot 1000} \quad (B.3)$$
+
+Definitions:
+
+- *frameSizes*: Vector containing the frame size in bytes for each frame in the video chunk.
+- *frameDuration*: Video frame duration in seconds, which is the same value for all frames in the video chunk.
+- *numVideoFrames*: Number of video frames in the chunk.
+
+Table B.1 shows coefficient sets for *quant* parameter calculation for mode 1.
+
+**Table B.1 – Coefficient sets for *quant* parameter calculation for mode 1**
+
+| Coefficient           | Value    |
+|-----------------------|----------|
+| <i>a</i> <sub>1</sub> | 5.00012  |
+| <i>a</i> <sub>2</sub> | −1.19631 |
+| <i>a</i> <sub>3</sub> | 41.35850 |
+
+### B.2 $Dq$ calculation for mode 1
+
+$Dq$  is calculated in the same manner as indicated in clause 8.1.1. For mode 1, however, there is an external correction factor not handled in the *quant* parameter, as outlined above, to include the effect of content-complexity.
+
+$$Dq = 100 - R_{fromMOS}(\widehat{MOSq}) \quad (B.4)$$
+
+(compare with clause 8.1.1 Equation (1)), where  $R_{fromMOS}$  is described in Annex E (same as in [ITU-T G.107]) and:
+
+$$Dq = \max(\min(Dq, 100), 0)$$
+
+and where:
+
+$$\widehat{MOSq}_1 = q_1 + q_2 \cdot \exp(q_3 \cdot quant) \quad (B.5)$$
+
+with the coefficients shown in Table B.2:
+
+**Table B.2 – Coefficients and values**
+
+| Coefficient | Value |
+|-------------|-------|
+| $q_1$       | 4.66  |
+| $q_2$       | -0.07 |
+| $q_3$       | 4.06  |
+
+In addition, we set:
+
+$$iFrameRatio = \frac{\bar{I}}{\bar{I}_n} \quad (B.6)$$
+
+with
+
+$\bar{I}$  : Average size of I-frames in chunk
+
+$\bar{I}_n$  : Average size of non-I-frames in chunk
+
+$$\widehat{MOSq} = \widehat{MOSq}_1 + \text{sigmoid}(c0, c1, c2, c3, iFrameRatio) \quad (B.7)$$
+
+where  $\text{sigmoid}(k0, k1, k2, iFrameRatio)$  is defined with a number of input parameters as follows:
+
+$$scalex = \frac{10}{k2 - k1} \quad (B.8)$$
+
+$$midx = \frac{k1 + k2}{2} \quad (B.9)$$
+
+$$\text{sigmoid}(k0, k1, k2, iFrameRatio) = k0 - \frac{k0}{1 + e^{-scalex \cdot (iFrameRatio - midx)}} \quad (B.10)$$
+
+The modelling coefficients in the sigmoid-function are set as shown in Table B.3:
+
+**Table B.3 – Settings of the modelling coefficients in the sigmoid-function**
+
+| Coefficient | Value       |
+|-------------|-------------|
+| $k0$        | -0.91562479 |
+| $k1$        | -3.28579526 |
+| $k2$        | 20.4098663  |
+
+The final score is calculated using the bounding function:
+
+$$\widehat{MOS}_q = \max(\min(\widehat{MOS}_q, 5), 1) \quad (\text{B.11})$$
+
+### **B.3 Performance analysis**
+
+See [ITU-T P.1203] for details on the performance of the complete model with the mode 1 Pv module.
+
+# Annex C
+
+## Mode 2 Pv module: *quant* description
+
+(This annex forms an integral part of this Recommendation.)
+
+## C.1 Consideration on parameter extraction
+
+In the case of mode 2, only 2% of bitstream data is allowed to be used. This has some implications for the way in which bitstream information is being parsed. Because the video module is run separately and the audio module used for all modes corresponds to the light-weight mode 0, the byte limit is enforced on video streams only. These considerations are described in the following:
+
+#### Payload not considered in the video byte count
+
+- Container metadata (e.g., TS headers, MP4 non-MDAT boxes, etc.)
+- [ITU-T H.264] Annex B start codes
+- Sequence parameter sets and picture parameter sets
+- The `nal_unit_type`, the `forbidden_zero_bit` and the `nal_ref_idc` indicator, i.e., the complete NAL unit header.
+
+In other words, the bytes counting towards the percentage limit correspond to the raw byte sequence payload (RBSP) as defined in [ITU-T H.264], including emulation prevention bytes in the NAL payload.
+
+#### C.1.1 Implications of 2%-limitation for frame-specific information
+
+It is noted that it may happen that some frames cannot be decoded, e.g., due to corrupted frames, bugs in the decoding software or if 2% of the frame is not enough information in order to extract information from a single frame. To compensate for such cases, the model includes a so called "frame compensation", which will allow the feature *quant* to be estimated more reliably. The frame compensation shall be run directly after bitstream parsing and before the estimation of the feature *quant*.
+
+To do this compensation, for every output sampling interval, first all frames within a chunk will be analysed whether there are bitstream statistics available or not, using the targeted 2% of bytes per frame. During this analysis, a vector *statsVec* of length  $N$ , where  $N$  is the number of frames in the chunk, is created consisting of a list of  $N$  tuples, where each tuple contains:
+
+- a boolean value and
+- the frame type
+
+per position/frame within this chunk. The *statsVec*'s frame types component can adopt the following values:
+
+- "I", "P", "B", used when there are bitstream statistics available
+- "I", "Non-I" where when those statistics are not present.
+
+Figure C.1 shows the overall pipeline of the compensation procedure:
+
+![Flowchart showing the relationship between frame information and workaround by going back to mode 1. The process starts with 'statsVec' pointing to a 'Bitstream statistics' box containing 'some frames', 'all frames', and 'no frames'. 'some frames' leads to 'compensate', which then leads to 'mode 2/3'. 'all frames' also leads to 'mode 2/3'. 'no frames' leads to 'mode 1'. Both 'mode 2/3' and 'mode 1' lead to 'score'. A small label 'P.1203.1(16)_FC.1' is at the bottom right.](e69b9188aa2c14ec6b21c83f711fef65_img.jpg)
+
+```
+
+graph TD
+    statsVec[statsVec] --> BitstreamStatistics[Bitstream statistics]
+    subgraph BitstreamStatistics
+        someFrames[some frames]
+        allFrames[all frames]
+        noFrames[no frames]
+    end
+    someFrames --> compensate[compensate]
+    allFrames --> mode23[mode 2/3]
+    noFrames --> mode1[mode 1]
+    compensate --> mode23
+    mode23 --> score[score]
+    mode1 --> score
+    P1203116_FC1[P.1203.1(16)_FC.1]
+  
+```
+
+Flowchart showing the relationship between frame information and workaround by going back to mode 1. The process starts with 'statsVec' pointing to a 'Bitstream statistics' box containing 'some frames', 'all frames', and 'no frames'. 'some frames' leads to 'compensate', which then leads to 'mode 2/3'. 'all frames' also leads to 'mode 2/3'. 'no frames' leads to 'mode 1'. Both 'mode 2/3' and 'mode 1' lead to 'score'. A small label 'P.1203.1(16)\_FC.1' is at the bottom right.
+
+**Figure C.1 – Relation between frame information and workaround by going back to mode 1 in the case of "no frames have stats" for a given chunk / model window**
+
+The previously created *statsVec* will now be analysed and classified dependent on the number of bitstream statistics available in the current chunk. There are three scenarios:
+
+- 1 No frame has bitstream statistics
+- 2 All frames have bitstream statistics
+- 3 Some frames have bitstream statistics.
+
+##### No frames have bitstream statistics
+
+In this case the model uses the algorithm specified in mode 1 for the calculation of the feature *quant*.
+
+##### All frames have bitstream statistics
+
+Since all frames can be decoded, there is no need for compensation. Therefore, the algorithm for the calculation of *quant* in mode 2/3 is applied directly.
+
+##### Some frames have bitstream statistics
+
+Since some frames have bitstream statistics it is possible to compensate for frames where no bitstream statistics are available in order to avoid the drawbacks of falling back to the mode 1 algorithm. This compensation is done in four steps:
+
+- 1 Iterate over all the frames in the chunk and generate *statsVec* (as described above).
+- 2 Iterate over *statsVec* starting at position *pos* = 0 where 0 is the index of the first frame in the chunk.
+- 3 If the frame at *pos* = 0 has statistics:
+  - a) Continue iterating *pos* until a frame without bitstream statistics is reached, store *statsPosLastFound* = *pos* - 1.
+  - b) Continue iterating *pos* until a frame with bitstream statistics is reached. The area between *pos* and *statsPosLastFound* + 1 is now called a "hole", i.e., a contiguous region of frames without bitstream statistics.
+  - c) For every frame within the hole at position *pos* with type *type*, call the function *findNearest(pos, type)* (as described below) in order to fill the bitstream statistics.
+- 4 If the frame at *pos* = 0 has no bitstream statistics:
+  - a) Set *statsPosLastFound* to -1
+
+b) Continue with step 3.b.
+
+##### **findNearest(pos, type)**
+
+This function searches for the nearest frame (starting at position *pos*) having bitstream statistics, which has the type *type*. If no frame matching these criteria can be found, the search is performed again, this time allowing any frame type to be matched.
+
+### **C.2 quant calculation**
+
+The quant parameter is calculated using the following formula:
+
+$$quant = \frac{\overline{QP_{PB}}}{51} \quad (C.1)$$
+
+Where  $\overline{QP_{PB}}$  is the average over all values in the vector  $QP_{PB}$ , where  $QP_{PB}$  is computed as described in the pseudocode below.
+
+Definitions:
+
+- *initialQP*: vector containing the initial quantization parameter (QP, with  $QP \in [0, 51]$ ) value for each frame in the video chunk;
+- *twoPercentQP*, a vector containing, for each frame in the video chunk, the average of the QP values for each complete macroblock (MB) contained in the first 2% (in bytes) of the current frame's payload. If the frame contains black borders on the top and bottom of the frame (so-called "letterboxing"), the QP values of the MBs contained in these black borders are ignored;
+- *frameTypes*, a vector containing the frame type for each video frame in the chunk.
+
+Here, video frames are parsed in their order of arrival and are therefore captured in decoding order, not in presentation/display order.
+
+Note: Array indices start at 0.
+
+```
+frameTypes ← [I,P,B,...]  
+QPPB ← []  
+p ← 2  
+index ← 0  
+  
+FOR frameType IN frameTypes:  
+  IF (frameType = P) OR (frameType = B):  
+    IF (twoPercentQP[index] = 0) OR  
+       (twoPercentQP[index] could not be computed) OR  
+       (p% for the frame contains only MBs in black border region):  
+      QPPB[index] ← initialQP[index]  
+    ELSE:  
+      QPPB[index] ← twoPercentQP[index]  
+  index ← index + 1
+```
+
+### **C.3 Performance analysis**
+
+See [ITU-T P.1203] for details on the performance of the complete model with the mode 2 Pv module.
+
+# Annex D
+
+## Mode 3 Pv module: *quant* description
+
+(This annex forms an integral part of this Recommendation.)
+
+$$quant = \frac{\overline{QP_{PB}}}{51} \quad (D.1)$$
+
+where  $\overline{QP_{PB}}$  is the average over all values in the vector  $QP_{PB}$ . For mode 3,  $QP_{PB}$  is computed as described in the pseudocode below.
+
+Definitions:
+
+- *numMBdec*: Vector containing the number of decoded MBs in the current frame for each video frame in the chunk.
+- *numMBskip*: Vector containing the number of skipped MBs in the current frame for each video frame in the chunk.
+- *averageQP*: Vector containing, for each video frame in the chunk, the average over the current frame of the QP values per MB, ignoring MBs in the black border areas, if the frame contains black borders.
+- *frameTypes*: Vector containing the frame types for each video frame in the chunk.
+
+Video frames are parsed from the bitstream and are therefore captured in decoding order.
+
+Note: Array indices start at 0.
+
+```
+frameTypes ← [I,P,B,...]
+QPP ← []
+QPB ← []
+QPPB ← []
+index ← 0
+
+FOR frameType IN frameTypes:
+
+  CASE frameType = P:
+
+    IF (length(QPP) = 0) OR
+       (numMBskip[index] / numMBdec[index] < 0.99):
+      QPP.append(averageQP[index])
+
+  CASE frameType = B:
+    QPB.append(averageQP[index])
+
+  CASE (frameType = I) AND (length(QPP) > 0):
+
+    IF length(QPP) > 1:
+      QPP[length(QPP)-1] ← QPP[length(QPP)-2]
+    ELSE:
+      QPP ← []
+
+  index ← index + 1
+
+QPPB ← QPP
+QPPB.append(QPB)
+```
+
+### **D.1 Performance analysis**
+
+See [ITU-T P.1203] for details on the performance of the complete model with the mode 3 Pv module.
+
+# Annex E
+
+## *MOSfromR* and *RfromMOS* and functions
+
+(This annex forms an integral part of this Recommendation.)
+
+## E.1 *MOSfromR* definition
+
+*MOSfromR* is expressed as follows:
+
+$$MOSfromR: \mathbb{R} \mapsto \mathbb{R}$$
+
+$$Q \mapsto MOS := MOSfromR(Q)$$
+
+$$MOS = MOS_{MIN} + (MOS_{MAX} - MOS_{MIN}) * \frac{Q}{100} + Q * (Q - 60) * (100 - Q) * 0.000007 \quad (E.1)$$
+
+$$MOS = \min(MOS_{MAX}, \max(MOS, MOS_{MIN})) \quad (E.2)$$
+
+where  $MOS_{MAX} = 4.9$  and  $MOS_{MIN} = 1.05$ .
+
+### E.2 *RfromMOS* definition
+
+*RfromMOS* is expressed as follows:
+
+$$RfromMOS: \mathbb{R} \mapsto \mathbb{R}$$
+
+$$MOS \mapsto Q := RfromMOS(MOS)$$
+
+It is the inverse function of *MOSfromR*.
+
+Since *RfromMOS* is not explicitly defined, the resulting value  $Q$  for a given  $MOS$  value shall be calculated using a lookup table based on *MOSfromR*, using linear interpolation.
+
+For the implementation of the inverse function, the absolute error of performing a double-conversion must be less than 0.01 in the  $MOS$  scale for all  $MOS$  values within the valid range  $[MOS_{MIN}, MOS_{MAX}]$ . In other words, it must be ensured that:
+
+$$|MOS - MOSfromR(RfromMOS(MOS))| < 0.01 \quad MOS \in [MOS_{MIN}, MOS_{MAX}] \quad (E.3)$$
+
+#### E.2.1 Example for lookup table
+
+The following algorithm gives an example of how to construct such a lookup table:
+
+Define a table  $h$  consisting of a unique set of keys  $K$  and a set of values  $V$ , where  $h(k)$  is the respective value  $v$  for the given key  $k$ . The lookup table must have only one value  $v$  for any given key  $k$ .
+
+Let  $h(MOSfromR(v)) = v$  for every  $v \in \{0, 0.25, 0.5, \dots, 100\}$  and let  $h(MOS_{MIN}) = 0$ .
+
+To obtain the value of  $Q$  for a given value of  $MOS$ , it must first be clipped to the allowed range:
+
+$$MOS = \min(MOS_{MAX}, \max(MOS, MOS_{MIN})) \quad (E.4)$$
+
+Then,  $Q$  is calculated based on a linear interpolation:
+
+$$Q = \frac{V_p(K_q - MOS) + V_q(MOS - K_p)}{K_q - K_p} \quad (\text{E. 5})$$
+
+where  $K_p, K_q$  are the nearest interpolation points available in  $h$ , and  $V_p, V_q$  the respective values at these points.
+
+# Annex F
+
+## Byte-counting algorithm for Mode 2
+
+(This annex forms an integral part of this Recommendation.)
+
+### Byte-counting algorithm
+
+Below is pseudocode that illustrates the expected behaviour of a conformant byte-counting implementation:
+
+```
+pv = PVModule(metaData)
+perFrameBytesConsumed = []
+bytesConsumed = 0
+totalBytes = 0
+for h264File in h264FileList:
+    byteStream = open(h264File)
+    while not eof:
+        consume start code at start of byteStream
+        nalUnitType = getNalUnitType(byteStream[0])
+        nextStartCodeOffset = findNextStartCode(byteStream)
+        nalUnit = byteStream[:nextStartCodeOffset]
+        if nalUnitType == SPS:
+            pv.consumeSps(nalUnit)
+        elif nalUnitType == PPS:
+            pv.consumePps(nalUnit)
+        elif nalUnitType in (IDR_SLICE, SLICE):
+            totalBytes += len(nalUnit) - 1
+            frameBytesConsumed = pv.consumeSliceNalUnit(nalUnit)
+            perFrameBytesConsumed.append(frameBytesConsumed)
+            bytesConsumed += frameBytesConsumed
+        byteStream = byteStream[nextStartCodeOffset:]
+pvScores = pv.getScores()
+assert bytesConsumed <= (totalBytes * 0.02), "Byte count exceeded"
+return (pvScores, perFrameBytesConsumed)
+```
+
+
+
+# SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | Tariff and accounting principles and international telecommunication/ICT economic and policy issues                                                       |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound-programme and television-transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                                                       |
+| Series Q        | Switching and signalling, and associated measurements and tests                                                                                           |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

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+
+
+# Recommendation
+
+# **ITU-T P.1211 (10/2023)**
+
+SERIES P: Telephone transmission quality, telephone installations, local line networks
+
+Models and tools for quality assessment of streamed media
+
+---
+
+# **Derivation procedure for contribution values to quality degradation of adaptive audiovisual streaming services**
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with white lines representing latitude and longitude, and the letters 'ITU' in a bold, blue, sans-serif font superimposed on the globe.
+
+ITU logo
+
+## ITU-T P-SERIES RECOMMENDATIONS
+
+### **Telephone transmission quality, telephone installations, local line networks**
+
+|                                                                                                    |                      |
+|----------------------------------------------------------------------------------------------------|----------------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality      | P.10-P.19            |
+| Voice terminal characteristics                                                                     | P.30-P.39            |
+| Reference systems                                                                                  | P.40-P.49            |
+| Objective measuring apparatus                                                                      | P.50-P.59            |
+| Objective electro-acoustical measurements                                                          | P.60-P.69            |
+| Measurements related to speech loudness                                                            | P.70-P.79            |
+| Methods for objective and subjective assessment of speech quality                                  | P.80-P.89            |
+| Voice terminal characteristics                                                                     | P.300-P.399          |
+| Objective measuring apparatus                                                                      | P.500-P.599          |
+| Measurements related to speech loudness                                                            | P.700-P.709          |
+| Methods for objective and subjective assessment of speech and video quality                        | P.800-P.899          |
+| Audiovisual quality in multimedia services                                                         | P.900-P.999          |
+| Transmission performance and QoS aspects of IP end-points                                          | P.1000-P.1099        |
+| Communications involving vehicles                                                                  | P.1100-P.1199        |
+| <b>Models and tools for quality assessment of streamed media</b>                                   | <b>P.1200-P.1299</b> |
+| Telemeeting assessment                                                                             | P.1300-P.1399        |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                  | P.1400-P.1499        |
+| Methods for objective and subjective assessment of quality of services other than speech and video | P.1500-P.1599        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T P.1211
+
+## Derivation procedure for contribution values to quality degradation of adaptive audiovisual streaming services
+
+## Summary
+
+Recommendation ITU-T P.1211 describes a derivation procedure for contribution values that provide information about a relationship between quality-influencing factors (e.g., media quality levels and stalling) and the final media session quality score of adaptive audiovisual streaming services. More precisely, contribution values show how much each quality-influencing factor affects (i.e., decreases) the final media session quality score provided by a quality estimation model (e.g., that of ITU-T P.1203 or ITU-T P.1204) using Shapley theory, which is a key concept in cooperative game theory for distributing profits in a game among participants. This derivation procedure can be used to monitor the streaming service since operators can ascertain which quality-influencing factors decrease the final media session quality score.
+
+## History \*
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID          |
+|---------|----------------|------------|-------------|--------------------|
+| 1.0     | ITU-T P.1211   | 2023-10-29 | 12          | 11.1002/1000/15695 |
+
+## Keywords
+
+Adaptive streaming, audiovisual, audiovisual quality estimation, contribution value, mean opinion score (MOS), monitoring, multimedia, QoE, Shapley theory.
+
+---
+
+\* To access the Recommendation, type the URL <https://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents/software copyrights, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2023
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                                                                                       | Page |
+|---------------------------------------------------------------------------------------------------------------------------------------|------|
+| 1 Scope .....                                                                                                                         | 1    |
+| 2 References.....                                                                                                                     | 2    |
+| 3 Definitions .....                                                                                                                   | 2    |
+| 3.1 Terms defined elsewhere .....                                                                                                     | 2    |
+| 3.2 Terms defined in this Recommendation.....                                                                                         | 3    |
+| 4 Abbreviations and acronyms .....                                                                                                    | 3    |
+| 5 Conventions .....                                                                                                                   | 3    |
+| 6 Field of application .....                                                                                                          | 4    |
+| 7 Building blocks .....                                                                                                               | 4    |
+| 7.1 Input data .....                                                                                                                  | 5    |
+| 8 Derivation procedure .....                                                                                                          | 6    |
+| Appendix I – Example of the deviation procedure with ITU-T P.1203 mode 0 (metadata-based model) as a quality estimation model .....   | 8    |
+| Appendix II – Example of the deviation procedure with ITU-T P.1203 mode 3 (bitstream-based model) as a quality estimation model ..... | 14   |
+| Appendix III – Example of the deviation procedure with [ITU-T P.1204.4] (pixel-based model) as a quality estimation model .....       | 17   |
+| Bibliography.....                                                                                                                     | 20   |
+
+
+
+## Derivation procedure for contribution values to quality degradation of adaptive audiovisual streaming services
+
+## 1 Scope
+
+This Recommendation describes a derivation procedure for contribution values that provides information about a relationship between a quality-influencing factor (i.e., media quality levels and stalling) and media session quality of adaptive audiovisual streaming services.
+
+In streaming services, the quality experienced by the end user can be assessed by using quality estimation models such as:
+
+- A metadata-based model, which uses audio and video bitrates, framerate, resolution ITU-T P.1203.1 mode 0, [ITU-T P.1203.2], [ITU-T P.1203.3];
+- A bitstream-based model that uses meta-data and any information from the video bitstream ITU-T P.1203.1 mode 3, [ITU-T P.1204.3], [ITU-T P.1203.2], [ITU-T P.1203.3];
+- A pixel-based model that uses information derived from reference video [ITU-T P.1204.4], [ITU-T P.1203.2], [ITU-T P.1203.3];
+- A hybrid metadata-based and pixel-based model [ITU-T P.1204.5], [ITU-T P.1203.2], [ITU-T P.1203.3].
+
+These models estimate a mean opinion score (MOS) on a five-point absolute category rating scale [ITU-T P.910] as a global multi-media MOS score [ITU-T P.911] by taking into account quality-influencing factors such as media quality level (i.e., set of audio-coding or video degradations due to coding, spatial re-scaling or variations in video frame rates) and stalling (i.e., delivery degradations due to initial loading delay and rebuffering at the client) [ITU-T P.1203]. In this Recommendation, the output of these quality estimation models (i.e., global multi-media MOS score) is referred to as the final media session quality score as specified in [ITU-T P.1203].
+
+The derivation procedure described provides contribution values that show how much each media quality level and stalling affects (i.e., decreases) the final media session quality score provided by quality estimation models such as [ITU-T P.1203] as previously described for each media session. This contribution value is calculated as the degree of quality degradation due to each media quality level and stalling by comparing with the maximum final media session quality score (i.e., the highest audiovisual quality and no stalling during the media session) based on Shapley theory, which is a key solution concept in cooperative game theory for distributing profits in a game among participants [b-Shapley]. Here, for example, different media quality levels selected or stalling occurrences during the media session result in different contribution values of each media quality level and stalling. Also, if the final media session quality score of a certain media session is different because of the use of a different quality estimation model, the contribution values of each media quality level and stalling are also different.
+
+The derivation procedure described is agnostic to the specified quality estimation models such as the ITU-T P.1203 type of model. This means that, although a metadata-based model (i.e., ITU-T P.1203 mode 0), bitstream-based model (i.e., ITU-T P.1203 mode 3), pixel-based model (i.e., [ITU-T P.1204.4]) and hybrid model (i.e., [ITU-T P.1204.5]), and their respective appendices for long term integration, generally exist to estimate the final media session quality score, this Recommendation can be used with all types of quality estimation model. As examples, the procedures when ITU-T P.1203 mode 0 (metadata-based model), ITU-T P.1203 mode 3 (bitstream-based model) and [ITU-T P.1204.4] (pixel-based model) are used as quality estimation model are described in Appendices I, II and III, respectively.
+
+This Recommendation primarily applies to the analysis of the quality aspect of progressive download or adaptive audiovisual streaming so that operators can ascertain degradation factors by deploying the derivation procedure described in end-point locations, mid-network monitoring points or a streaming server.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T P.910] Recommendation ITU-T P.910 (2023), *Subjective video quality assessment methods for multimedia applications.*
+- [ITU-T P.911] Recommendation ITU-T P.911 (1998), *Subjective audiovisual quality assessment methods for multimedia applications.*
+- [ITU-T P.1203] Recommendation ITU-T P.1203 (2017), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport.*
+- [ITU-T P.1203.1] Recommendation ITU-T P.1203.1 (2019), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Video quality estimation module.*
+- [ITU-T P.1203.2] Recommendation ITU-T P.1203.2 (2017), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Audio quality estimation module.*
+- [ITU-T P.1203.3] Recommendation ITU-T P.1203.3 (2019), *Parametric bitstream-based quality assessment of progressive download and adaptive audiovisual streaming services over reliable transport – Quality integration module.*
+- [ITU-T P.1204] Recommendation ITU-T P.1204 (2020), *Video quality assessment of streaming services over reliable transport for resolutions up to 4K.*
+- [ITU-T P.1204.3] Recommendation ITU-T P.1204.3 (2020), *Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full bitstream information.*
+- [ITU-T P.1204.4] Recommendation ITU-T P.1204.4 (2022), *Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full and reduced reference pixel information.*
+- [ITU-T P.1204.5] Recommendation ITU-T P.1204.5 (2023), *Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to transport and received pixel information.*
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 adaptation set** [ITU-T P.1203]: A set of distinct media quality levels to be used for HTTP adaptive streaming, between which the player can perform media adaptation.
+
+**3.1.2 mean opinion score (MOS)** [b-ITU-T P.10]: The mean of opinion scores.
+
+**3.1.3 media quality level** [ITU-T P.1203]: A particular encoding setting applied to a video or audio stream.
+
+**3.1.4 segment** [ITU-T P.1203]: An audiovisual file belonging to one particular media quality level.
+
+**3.1.5 sequence** [ITU-T P.1203]: An audiovisual stream composed of multiple non-overlapping segments.
+
+### **3.2 Terms defined in this Recommendation**
+
+This Recommendation defines the following terms:
+
+**3.2.1 maximum media session quality score**: The final media session quality score for a certain sequence in which only the highest media quality level is selected, and no stalling occurs.
+
+**3.2.2 modified sequence**: A sequence in which specified selected media quality levels during a media session are replaced by the highest media quality level in an adaptation set or the number of stalling occurrences is replaced by zero.
+
+**3.2.3 stalling**: Stalling is caused by initial loading delay and rebuffering events at the client side, which could be a result of video data arriving late. Usually, stalling events are indicated to the viewer, e.g., in the form of a spinning wheel, and result in stalling of the media playout.
+
+## **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+AAC Advanced Audio Coding
+
+AC3 Audio Compression 3
+
+FQ Final Quality
+
+HE High Efficiency
+
+HRC Hypothetical Reference Circuit
+
+HTTP Hyper Text Transfer Protocol
+
+LC Low Complexity
+
+MO Mobile
+
+MOS Mean Opinion Score
+
+PC Personal Computer
+
+PVS Processed Video Sequence
+
+TA Tablet
+
+TV Television
+
+VP9 Video Payload type 9
+
+## **5 Conventions**
+
+None.
+
+## 6 Field of application
+
+This Recommendation analyses the quality aspect of progressive download streaming or adaptive bitrate streaming. Limitations regarding the transport protocol, video length or encoding protocol and other attributes related to streaming services are the same as those of the quality estimation model used since the procedure described requires the final media session quality score from it.
+
+The procedure described is used on a server providing streaming service, as shown in Figure 1. After finishing a video playback on a client device, stalling information is sent to the streaming server. The contribution values are then calculated by a derivation procedure described in this Recommendation using a quality estimation model and selected quality level during media sessions that are on the streaming server.
+
+The contribution values are generally calculated on the streaming server so that operators can ascertain degradation factors. This is because the contribution calculation needs bitstream or pixel information of the highest media quality level at each segment, which is stored on a streaming server and not on a client device, if the bitstream-based (i.e., ITU-T P.1203 mode 3) or pixel-based (i.e., [ITU-T P.1204.4]) quality estimation model is used. However, if the metadata-based quality estimation model (i.e., ITU-T P.1203 mode 0) is used, the contribution values can be calculated on the client device since the metadata-based quality estimation model can be executed there and the metadata of the highest media quality level is also found on that site.
+
+![Sequence diagram showing the interaction between a Streaming server and a Client. The sequence is: 1. Send media information (server to client), 2. Video playback (client), 3. Send stalling information (client to server), 4. Calculate contribution values (server).](daa4a6fa7e2ba1954258f86b4928eb32_img.jpg)
+
+```
+sequenceDiagram
+    participant Streaming server
+    participant Client
+    Note right of Client: P.1211(23)
+    Streaming server->>Client: 1. Send media information
+    Note right of Client: 2. Video playback
+    Client->>Streaming server: 3. Send stalling information
+    Note left of Streaming server: 4. Calculate contribution values
+```
+
+Sequence diagram showing the interaction between a Streaming server and a Client. The sequence is: 1. Send media information (server to client), 2. Video playback (client), 3. Send stalling information (client to server), 4. Calculate contribution values (server).
+
+**Figure 1 – Sequence diagram**
+
+## 7 Building blocks
+
+The building blocks are depicted in Figure 2. This Recommendation uses the selected quality level sequence and stalling information extracted from the sequence and final media session quality score output from a quality estimation module. In addition to that, if the bitstream-based or pixel-based quality estimation model is used, bitstream information or pixel information is needed as shown in Figure 2. The details are described in clause 7.1.
+
+During the calculation of contribution values, since the derivation procedure requires its final media session quality score, the modified sequence is sent to the quality estimation module. Here, in a modified sequence, specified selected media quality levels during media session are replaced by the highest media quality level in an adaptation set or the number of stalling occurrences is replaced by zero. The details of the modified sequence are explained in clause 8. The derivation procedure described also needs adaptation set information, which is prepared at the streaming server.
+
+![Figure 2 – Building blocks. A block diagram showing the flow of data from a 'Sequence' input through three parallel extraction modules: 'Media parameter extraction', 'Pixel information extraction', and 'Stalling extraction'. These modules feed into a central 'Audiovisual quality estimation module (e.g., ITU-T P.1203)'. This module also receives 'Reference video pixel information' and an 'Adaptation set and bitstream and pixel information of highest media quality level'. The output of the quality estimation module is a 'Final media session quality score (e.g., 0.46)' and a 'Modified sequence'. These outputs, along with the extracted information, feed into a 'Contribution value estimation module'. The final output is 'Contribution values'. The diagram is labeled P.1211(23) in the bottom right corner.](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+Figure 2 – Building blocks. A block diagram showing the flow of data from a 'Sequence' input through three parallel extraction modules: 'Media parameter extraction', 'Pixel information extraction', and 'Stalling extraction'. These modules feed into a central 'Audiovisual quality estimation module (e.g., ITU-T P.1203)'. This module also receives 'Reference video pixel information' and an 'Adaptation set and bitstream and pixel information of highest media quality level'. The output of the quality estimation module is a 'Final media session quality score (e.g., 0.46)' and a 'Modified sequence'. These outputs, along with the extracted information, feed into a 'Contribution value estimation module'. The final output is 'Contribution values'. The diagram is labeled P.1211(23) in the bottom right corner.
+
+**Figure 2 – Building blocks**
+
+### 7.1 Input data
+
+This Recommendation uses the adaptation set information at a streaming server [ITU-T P.1203], which consists of multiple media quality levels (i.e., multiple levels of tuple of audio bitrate, video bitrate, video resolution, and video frame rate), a sequence that is a history of selected media quality levels during a media session, stalling information tuple (i.e., start time and duration of stalling [ITU-T P.1203.3]) during a media session, and the final media session quality score. In addition, if the bitstream-based quality estimation model is used, bitstream information of the selected quality levels during the media session is extracted from the sequence and the bitstream information of the highest media quality level at each segment, is needed as shown in Figure 2. When a pixel-based quality estimation model is used, video pixel information of the selected quality levels is extracted from the sequence and pixel information of the highest media quality level, and video reference pixel information obtained as input, are needed. Appendices II and III describe how to use the information.
+
+Let  $N = \{r_1, \dots, r_R, s\}$  be a set of an adaptation set (i.e., prepared media quality levels on a streaming server) and stalling information, where  $r_1$  is the lowest media quality level,  $r_R$  is the highest media quality level,  $R$  is the number of media quality levels, and  $s$  represents all stalling events. Here, media quality level is the tuple of audio bitrate, video bitrate, video resolution, and video frame rate. Let  $x_j \in N$  be the  $j$ th element in  $N$ ,  $j = 1, \dots, R + 1$ .  $H$  denotes the sequence, which consists of selected media quality levels  $r_i$  and all stalling events  $s$  during video playback. The notation used in this Recommendation is listed in Table 1.
+
+Note that, since the quality estimation model is used during the contribution value calculation, the input data in this Recommendation is specified by the input data of the quality estimation model. As examples, the specific input data is described if the ITU-T P.1203 mode 0, ITU-T P.1203 mode 3 or ITU-T P.1204 is used in Appendices I, II and III.
+
+**Table 1 – Notation used in this Recommendation**
+
+| Symbol                       | Description                                                                                                                                                                                                                                                                                                                            |
+|------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| $N = \{r_1, \dots, r_R, s\}$ | A set of adaptation set and stalling information. $r_1$ is the lowest media quality level, $r_R$ is the highest media quality level, $R$ is the number of media quality levels, and $s$ represents all stalling events. Here, media quality level is the tuple of audio bitrate, video bitrate, video resolution, and video frame rate |
+| $x_j$                        | $j$ th element in $N, j = 1, \dots, R + 1$ .                                                                                                                                                                                                                                                                                           |
+| $Z$                          | All of subsets of $N$ without $x_j$ .                                                                                                                                                                                                                                                                                                  |
+| $z_i$                        | One of the elements of $Z. z_i \in Z, i = 1, \dots,  Z $                                                                                                                                                                                                                                                                               |
+| $H$                          | A sequence, that consists of selected media quality level $r_i$ and all stalling events $s$ during video playback.                                                                                                                                                                                                                     |
+| $H'$ (or $H''$ )             | A modified sequence of an input sequence $H$ and $z_i$ , in which a part of the selected media quality level during a media session is replaced with the highest media quality level in an adaptation set.                                                                                                                             |
+| $f$                          | A function that takes a given $H$ and subset $z_i$ (or $z_i \cup x_j$ ) as input and outputs a modified sequence $H'$ (or $H''$ ).                                                                                                                                                                                                     |
+| $v$                          | A quality estimation model such as that of [ITU-T P.1203] or [ITU-T P.1204], which estimates the quality of an input sequence, $H$ .                                                                                                                                                                                                   |
+| $c_j$                        | Contribution value of $x_j$ .                                                                                                                                                                                                                                                                                                          |
+
+## 8 Derivation procedure
+
+The derivation procedure for contribution values consists of three steps, which are summarized in Table 2.
+
+**Table 2 – Calculation steps of contribution values**
+
+| Step | Description                                                                                                          |
+|------|----------------------------------------------------------------------------------------------------------------------|
+| 1    | Pick up one element $x_j$ in $N$ and iterate steps 2 and 3 for over all elements $x_j$ in $N, j = 1, \dots, R + 1$ . |
+| 2    | Determine the set $Z$ consisting of all subsets of $N$ without $x_j$ .                                               |
+| 3    | Calculate the contribution value, $c_j$ , of $x_j$ by adapting the Shapley value calculation given in Equation 1.    |
+
+The first step is to pick up one element  $x_j$  and iterate steps 2 and 3 for over all elements  $x_j$  in  $N$ . Here, the order of picking up element in  $N$  does not affect the calculation results. For simplicity, the case  $x_j$  is explained in the following. However, the procedure described is executed over all elements in  $N$  to calculate all contribution values,  $c_j, j = 1, \dots, R, R + 1$ . The second step is to determine the composition of all subsets  $Z$  of  $N$  without  $x_j$ . Here,  $Z$  is all possible patterns of subsets induced from  $N$  without  $x_j$ , and the cardinality of  $Z$  is  $2^{|N|-1}$ . The third step is to calculate the contribution value,  $c_j$ , of  $x_j$  by adapting the Shapley value calculation.
+
+The details of the third step, in which the contribution value,  $c_j$ , of  $x_j$  is calculated, are as follows. Let  $f$  be a function that takes a given sequence  $H$  and subset  $z_i \in Z, i = 1, \dots, |Z|$  (or  $z_i \cup x_j$ ) as input and outputs a modified sequence,  $H'$  (or  $H''$ ). Let  $v$  be a quality estimation model such as that of [ITU-T P.1203] or [ITU-T P.1204], which estimates the quality of an input sequence,  $H$ . From here,
+
+although the contribution value calculation algorithm is explained only for a given subset,  $z_i$ , it is also applicable to other subsets,  $(z_i \cup x_j)$ . The modification procedure is described in the following paragraphs. The contribution value,  $c_j$ , of  $x_j$  is calculated by adopting the Shapley value calculation algorithm as follows.
+
+$$c_j(v, f, H) = \sum_{i=1}^{|Z|} \frac{|z_i|!(|N|-|z_i|-1)!}{|N|!} \left( v(f(z_i, H)) - v(f(z_i \cup x_j, H)) \right) \quad (1)$$
+
+where  $|Z|$  and  $|N|$  denote the cardinality of  $Z$  and  $N$ , respectively, and the sum extends over all subsets,  $z_i \in Z$ , which are the subsets of  $N$  that do not include  $x_j$ .
+
+The function  $f$  maps a subset  $z_i$  and a sequence of quality levels  $H = (h_t)$  to a new sequence of quality levels  $H' = (h'_t)$  by replacing all occurrences of quality levels in  $z_i$  by the highest quality level  $r_R$ ,
+
+$$h'_t = \begin{cases} r_R & \text{if } h_t \in z_i \\ h_t & \text{otherwise} \end{cases} \quad (2)$$
+
+For the stalling, if  $s$  is in  $z_i$ ,  $f$  generates  $H'$  in which the stalling events are removed, while if  $s$  is not in  $z_i$ ,  $f$  generates  $H'$  in which stalling information is the same as the original  $H$ .
+
+For the case,  $z_i \cup x_j$ ,  $f$  outputs  $H''$  similarly to modifying  $H$  to  $H'$ . By generating sequences  $H'$  and  $H''$  on the basis of a given subset  $z_i$  and calculating the quality decrease over all possible subsets using Equation (1), the contribution value,  $c_j$ , of  $x_j$  is calculated.
+
+## Appendix I
+
+### Example of the deviation procedure with ITU-T P.1203 mode 0 (metadata-based model) as a quality estimation model
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This appendix describes the example of the deviation procedure when ITU-T P.1203 mode 0 is used as a quality estimation model. Especially, prepared processed video sequences (PVSs), input data specification, and contribution values are described.
+
+#### Prepared PVSs
+
+In this example, four PVSs listed under this heading are used to show the derivation procedure and the contribution values for various kinds of hypothetical reference circuit (HRC). These PVSs are generated on the basis of the HRC of an ITU-T P.1203 open dataset [b-Robitza] by using a prepared source video, which is 1 min long. The characteristics of these PVSs follow and the HRCs used are shown in Figures I.1 and I.2. Table I.1 shows the media quality level of the HRC.
+
+PVS01: HRC80 in TR04 [b-Robitza] in which only one media quality level is selected during a media session with no stalling.
+
+PVS02: HRC03 TR04 [b-Robitza] in which multiple media quality levels are selected during a media session with no stalling.
+
+PVS03: HRC85 in TR04 [b-Robitza] in which multiple media quality levels are selected and a stalling occurs during a media session.
+
+PVS04: HRC02 in TR04 [b-Robitza] in which multiple media quality levels are selected and stalling occurs multiple times during a media session.
+
+![Figure I.1: Bitrate (kbit/s) vs Viewing time (s) for HRC80 and HRC03 in TR04 in ITU-T P.1203 open dataset [b-Robitza]. The left graph shows a constant bitrate of 500 kbit/s for HRC80. The right graph shows a variable bitrate for HRC03, with values of 2500, 500, 250, 500, 2500, 500, 250, 500, 2500, 500, 250, 500 kbit/s over 60 seconds.](70f5f44cb855bbb0c203c00187b2113e_img.jpg)
+
+Figure I.1 consists of two line graphs. The left graph, representing HRC80, shows a constant bitrate of 500 kbit/s over a 60-second viewing time. The right graph, representing HRC03, shows a variable bitrate over the same 60-second period. The HRC03 graph is a step function with the following bitrates: 2500 kbit/s (0-5s), 500 kbit/s (5-10s), 250 kbit/s (10-15s), 500 kbit/s (15-20s), 2500 kbit/s (20-25s), 500 kbit/s (25-30s), 250 kbit/s (30-35s), 500 kbit/s (35-40s), 2500 kbit/s (40-45s), 500 kbit/s (45-50s), 250 kbit/s (50-55s), and 500 kbit/s (55-60s).
+
+| Viewing time (s) | HRC80 Bitrate (kbit/s) | HRC03 Bitrate (kbit/s) |
+|------------------|------------------------|------------------------|
+| 0 - 5            | 500                    | 2500                   |
+| 5 - 10           | 500                    | 500                    |
+| 10 - 15          | 500                    | 250                    |
+| 15 - 20          | 500                    | 500                    |
+| 20 - 25          | 500                    | 2500                   |
+| 25 - 30          | 500                    | 500                    |
+| 30 - 35          | 500                    | 250                    |
+| 35 - 40          | 500                    | 500                    |
+| 40 - 45          | 500                    | 2500                   |
+| 45 - 50          | 500                    | 500                    |
+| 50 - 55          | 500                    | 250                    |
+| 55 - 60          | 500                    | 500                    |
+
+Figure I.1: Bitrate (kbit/s) vs Viewing time (s) for HRC80 and HRC03 in TR04 in ITU-T P.1203 open dataset [b-Robitza]. The left graph shows a constant bitrate of 500 kbit/s for HRC80. The right graph shows a variable bitrate for HRC03, with values of 2500, 500, 250, 500, 2500, 500, 250, 500, 2500, 500, 250, 500 kbit/s over 60 seconds.
+
+Figure I.1 – HRC80 and HRC03 in TR04 in ITU-T P.1203 open dataset [b-Robitza]
+
+![Two line graphs showing Bitrate (kbit/s) vs Viewing time (s) for HRC85 and HRC02. The left graph for HRC85 shows a sawtooth pattern between 500 and 2500 kbit/s over 60 seconds. The right graph for HRC02 shows a step-like pattern between 250 and 2500 kbit/s over 80 seconds. A label 'P.1211(23)' is in the bottom right corner.](71ab4df17511d75261da8d462d643b1a_img.jpg)
+
+Two line graphs showing Bitrate (kbit/s) vs Viewing time (s) for HRC85 and HRC02. The left graph for HRC85 shows a sawtooth pattern between 500 and 2500 kbit/s over 60 seconds. The right graph for HRC02 shows a step-like pattern between 250 and 2500 kbit/s over 80 seconds. A label 'P.1211(23)' is in the bottom right corner.
+
+**Figure I.2 – HRC85 and HRC02 in TR04 in ITU-T P.1203 open dataset [b-Robitza]**
+
+**Table I.1 – Media quality level information of PVSs**
+
+NOTE – Quality levels QL1, QL3, and QL5 are not defined in this dataset [b-Robitza].
+
+| Quality level | Video bitrate (kbit/s) | Resolution (pixel) |
+|---------------|------------------------|--------------------|
+| QL7           | 10 000                 | 1 080              |
+| QL6           | 2 500                  | 1 080              |
+| QL4           | 500                    | 480                |
+| QL2           | 150                    | 240                |
+
+#### Input data specifications
+
+The input data of this Recommendation is the adaptation set information, a sequence that is a history of selected media quality levels during a media session, stalling information during a media session and the final media session quality score. The input data are specified in Table I.2, where the listed input data is based on ITU-T P.1203.1 mode 0, [ITU-T P.1203.2] and ITU-T P.1203.3].
+
+**Table I.2 – Input specifications**
+
+| Description                                             | Values                                               | Frequency         |
+|---------------------------------------------------------|------------------------------------------------------|-------------------|
+| The resolution of the image displayed to the user       | Number of pixels ( $W \times H$ ) in displayed video | Per media chunk   |
+| The device type on which the media is played            | "PC", "TV", "MO", "TA"                               | Per media chunk   |
+| Device display size                                     | Display size (diagonal in inches)                    | Per media chunk   |
+| Relative viewing distance in multiple of display height | Relative viewing distance                            | Per media chunk   |
+| Target Audio bitrate                                    | Bitrate in kilobits per second                       | Per media segment |
+| Segment duration                                        | Duration in seconds                                  | Per media segment |
+| Audio codec                                             | One of: AAC-LC, AAC-HEv1, AAC-HEv2, AC3              | Per media segment |
+| Audio sampling frequency                                | In hertz                                             | Per media segment |
+| Number of audio channels                                | 2                                                    | Per media segment |
+
+**Table I.2 – Input specifications**
+
+| Description                             | Values                                                                                                                                                                                         | Frequency          |
+|-----------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| Video target bitrate                    | Bitrate in kilobits per second                                                                                                                                                                 | Per media chunk    |
+| Video frame rate                        | Frame rate in frames per second.                                                                                                                                                               | Per media chunk    |
+| Segment duration                        | Duration in seconds                                                                                                                                                                            | Per media chunk    |
+| Video encoding resolution               | Number of pixels ( $W \times H$ ) in transmitted video                                                                                                                                         | Per media chunk    |
+| Video codec and profile                 | ITU-T H.264-high                                                                                                                                                                               | Per media chunk    |
+| Stalling or initial loading event start | The start time of the stalling event in seconds relative to the start of the original video clip, expressed in media time (not wall clock time)<br>NOTE – This is 0 for initial loading delay. | Per stalling event |
+| Event duration                          | The duration of the stalling event in seconds                                                                                                                                                  | Per stalling event |
+| Final media session quality score       | Scores provided per session and on a quality scale of 1 to 5                                                                                                                                   | Per session        |
+
+Legend – AAC: advanced audio coding; AC3: audio compression 3; HE: high efficiency; LC: low complexity; MO: mobile; MPEG: Moving Picture Experts Group; PC: personal computer; TA: tablet; TV: television; VP9: video payload type 9.
+
+#### **Example of calculation steps**
+
+An example calculation step is described. Assume a sequence and adaptation set as follows.
+
+$$H = [QL4, QL6, QL2, QL2, QL7], N = \{QL7, QL6, QL4, QL2, s\},$$
+
+where,  $H$  has no stalling. The first step of the calculation is to select  $x_j$  from  $N$  and determine all of subset  $Z$ . Assume that the selected  $x_j$  in the iteration of step 1 is  $QL2$ ,
+
+$$x_j = QL2,$$
+
+and  $Z$  will be determined, according to Table 2, as all the patterns of subsets of  $N$  without  $x_j$ , which is
+
+$$\begin{aligned} Z = \{ & z_1 = \{QL4\}, z_2 = \{QL6\}, z_3 = \{QL7\}, z_4 = \{s\}, z_5 = \{QL4, QL6\}, z_6 = \{QL4, QL7\}, z_7 \\ & = \{QL4, s\}, z_8 = \{QL6, QL7\}, z_9 = \{QL6, s\}, z_{10} = \{QL7, s\}, z_{11} \\ & = \{QL4, QL6, QL7\}, z_{12} = \{QL4, QL6, s\}, z_{13} = \{QL4, QL7, s\}, z_{14} \\ & = \{QL6, QL7, s\}, z_{15} = \{QL4, QL6, QL7, s\}, z_{16} = \{\} \}. \end{aligned}$$
+
+Then,  $z_i$  is selected from  $Z$  to modify the sequence  $H$ . For instance, if  $z_1$  is selected,
+
+$$z_1, \{z_1 \cup x_j\} = \{QL2, QL4\}.$$
+
+Then, by using Equation (2), the modified sequence is generated. In this case, since  $QL2$  and  $QL4$  are in subsets  $z_1$  and  $\{z_1 \cup x_j\}$ ,  $H'$  and  $H''$  become as follows.
+
+$$H' = [\mathbf{QL7}, QL6, QL2, QL2, QL7], v(H') = 2.880$$
+
+$$H'' = [\mathbf{QL7}, QL6, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.885$$
+
+The bold segments are replaced with the highest media quality level in  $N$  and the final media session quality score of both sequence  $H'$  and  $H''$  is calculated using ITU-T P.1203 mode 0. Then, the part of the contribution values is calculated as follows.
+
+$$\frac{|z_1|! (|N| - |z_1| - 1)!}{|N|!} (v(f(z_1, H)) - v(f(z_1 \cup x_j, H))) = \frac{1! 3!}{5!} (2.880 - 4.885) = -0.100.$$
+
+Note that, the outputs of  $v$  is rounded to the fourth decimal place.
+
+This process is executed over all elements in  $Z$  as follows. From here onwards, the term
+
+$$\frac{|z_i|! (|N| - |z_i| - 1)!}{|N|!} (v(f(z_i, H)) - v(f(z_i \cup x_j, H)))$$
+
+is denoted  $E$ .
+
+- For  $z_2$ 
+  - $z_2, \{z_2 \cup x_j\} = \{QL2, QL6\}.$
+  - $H' = [QL4, \mathbf{QL7}, QL2, QL2, QL7], v(H') = 2.822,$
+  - $H'' = [QL4, \mathbf{QL7}, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.425$
+  - $E = \frac{1!3!}{5!} (2.822 - 4.425) = -0.080$
+- For  $z_3$ 
+  - $z_3, \{z_3 \cup x_j\} = \{QL2, QL7\}.$
+  - $H' = [QL4, QL6, QL2, QL2, QL7], v(H') = 2.822,$
+  - $H'' = [QL4, QL6, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.423$
+  - $E = \frac{1!3!}{5!} (2.822 - 4.423) = -0.080$
+- For  $z_4$ 
+  - $z_4, \{z_4 \cup x_j\} = \{QL2, s\}.$
+  - $H' = [QL4, QL6, QL2, QL2, QL7], v(H') = 2.822,$
+  - $H'' = [QL4, QL6, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.423$
+  - $E = \frac{1!3!}{5!} (2.822 - 4.423) = -0.080$
+- For  $z_5$ 
+  - $z_5, \{z_5 \cup x_j\} = \{QL2, QL4, QL6\}.$
+  - $H' = [\mathbf{QL7}, \mathbf{QL7}, QL2, QL2, QL7], v(H') = 2.880,$
+  - $H'' = [\mathbf{QL7}, \mathbf{QL7}, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.896$
+  - $E = \frac{2!2!}{5!} (2.880 - 4.896) = -0.067$
+- For  $z_6$ 
+  - $z_6, \{z_6 \cup x_j\} = \{QL2, QL4, QL7\}.$
+  - $H' = [\mathbf{QL7}, QL6, QL2, QL2, QL7], v(H') = 2.880,$
+  - $H'' = [\mathbf{QL7}, QL6, \mathbf{QL7}, \mathbf{QL7}, QL7], v(H'') = 4.885$
+  - $E = \frac{2!2!}{5!} (2.880 - 4.885) = -0.067$
+- For  $z_7$ 
+  - $z_7, \{z_7 \cup x_j\} = \{QL2, QL4, s\}.$
+
+- $H' = [QL7, QL6, QL2, QL2, QL7], v(H') = 2.880,$
+- $H'' = [QL7, QL6, QL7, QL7, QL7], v(H'') = 4.885$
+- $E = \frac{2!2!}{5!} (2.880 - 4.885) = -0.067$
+
+– For  $z_8$
+
+- $z_8, \{z_8 \cup x_j\} = \{QL2, QL6, QL7\}.$
+- $H' = [QL4, QL7, QL2, QL2, QL7], v(H') = 2.822,$
+- $H'' = [QL4, QL7, QL7, QL7, QL7], v(H'') = 4.425$
+- $E = \frac{2!2!}{5!} (2.822 - 4.425) = -0.053$
+
+– For  $z_9$
+
+- $z_9, \{z_9 \cup x_j\} = \{QL2, QL6, s\}.$
+- $H' = [QL4, QL7, QL2, QL2, QL7], v(H') = 2.822,$
+- $H'' = [QL4, QL7, QL7, QL7, QL7], v(H'') = 4.425$
+- $E = \frac{2!2!}{5!} (2.822 - 4.425) = -0.053$
+
+– For  $z_{10}$
+
+- $z_{10}, \{z_{10} \cup x_j\} = \{QL2, QL7, s\}.$
+- $H' = [QL4, QL6, QL2, QL2, QL7], v(H') = 2.822,$
+- $H'' = [QL4, QL6, QL7, QL7, QL7], v(H'') = 4.423$
+- $E = \frac{2!2!}{5!} (2.822 - 4.423) = -0.053$
+
+– For  $z_{11}$
+
+- $z_{11}, \{z_{11} \cup x_j\} = \{QL2, QL4, QL6, QL7\}.$
+- $H' = [QL7, QL7, QL2, QL2, QL7], v(H') = 2.880,$
+- $H'' = [QL7, QL7, QL7, QL7, QL7], v(H'') = 4.896$
+- $E = \frac{3!1!}{5!} (2.880 - 4.896) = -0.100$
+
+– For  $z_{12}$
+
+- $z_{12}, \{z_{12} \cup x_j\} = \{QL2, QL4, QL6, s\}.$
+- $H' = [QL7, QL7, QL2, QL2, QL7], v(H') = 2.880,$
+- $H'' = [QL7, QL7, QL7, QL7, QL7], v(H'') = 4.896$
+- $E = \frac{3!1!}{5!} (2.880 - 4.896) = -0.100$
+
+– For  $z_{13}$
+
+- $z_{13}, \{z_{13} \cup x_j\} = \{QL2, QL4, QL7, s\}.$
+- $H' = [QL7, QL6, QL2, QL2, QL7], v(H') = 2.880,$
+- $H'' = [QL7, QL6, QL7, QL7, QL7], v(H'') = 4.885$
+- $E = \frac{3!1!}{5!} (2.880 - 4.885) = -0.100$
+
+– For  $z_{14}$
+
+- $z_{14}, \{z_{14} \cup x_j\} = \{QL2, QL6, QL7, s\}.$
+- $H' = [QL4, QL7, QL2, QL2, QL7], v(H') = 2.822$
+- $H'' = [QL4, QL7, QL7, QL7, QL7], v(H'') = 4.425$
+- $E = \frac{3!1!}{5!} (2.822 - 4.425) = -0.080$
+
+– For  $z_{15}$
+
+- $z_{15}, \{z_{15} \cup x_j\} = \{QL2, QL4, QL6, QL7, s\}.$
+- $H' = [QL7, QL7, QL2, QL2, QL7], v(H') = 2.880,$
+- $H'' = [QL7, QL7, QL7, QL7, QL7], v(H'') = 4.896$
+- $E = \frac{4!0!}{5!} (2.880 - 4.896) = -0.403$
+
+– For  $z_{16}$
+
+- $z_{16}, \{z_{16} \cup x_j\} = \{QL2\}.$
+- $H' = [QL4, QL6, QL2, QL2, QL7], v(H') = 2.822,$
+- $H'' = [QL4, QL6, QL7, QL7, QL7], v(H'') = 4.423$
+- $E = \frac{0!4!}{5!} (2.822 - 4.423) = -0.320$
+
+Finally, the contribution value  $c_j$  of  $x_j$  (i.e., QL2) can be obtained by summing  $E$  from  $z_1$  to  $z_{16}$ . In this example case,  $c_j$  is  $-1.807$ . To calculate contribution values for QL4, QL6, QL7, and stalling, the preceding process is repeated.
+
+Note that as described in clause 6, since all information to estimate the quality of modified sequence  $H'$  and  $H''$  is from the metadata-based model, the contribution calculation can be executed on the client device.
+
+#### Calculation results
+
+Table I.3 shows the calculated contribution values. In Table I.3, final quality (FQ) means the final media session quality score of corresponding PVS calculated by ITU-T P.1203 mode 0. QL7, QL6, QL4, QL2, and stalling columns mean the contribution value of each media quality level. The column total means the total value of contribution value.
+
+In PVS01, since QL7, QL6 and QL2 are not selected and do not induce any quality degradation, the contribution value equals 0. Also, since stalling does not occur or induce any quality degradation, the contribution value equals 0. On the other hand, since QL4 was selected during a media session, it has  $-1.375$  points. This means that QL4 reduces the final media session quality score by approximately 1.375 compared with the maximum media session quality score. In PVS02, QL6, QL4 and QL2 were selected. Thus, each media quality level reduced the FQ, and QL2 reduced the quality the most. In PVS03, since stalling occurred, the contribution value of the stalling was  $-0.375$ . In PVS04, since several quality levels were selected, each quality level reduces the quality. Specifically, since stalling occurred twice and media quality level QL2 was selected many times in this PVS, the stalling and QL2 reduced the final media session quality score. These contribution values of each PVS also indicate that if the PVS differs, the contribution values of each PVS also differ since the selected media quality level or stalling occurrence differs between PVSs.
+
+**Table I.3 – Calculated results of contribution values for PVS01, PVS02, PVS03, and PVS04**
+
+|       | FQ    | QL7 | QL6    | QL4    | QL2    | Stalling | Total  |
+|-------|-------|-----|--------|--------|--------|----------|--------|
+| PVS01 | 3.531 | 0   | 0      | -1.357 | 0      | 0        | -1.357 |
+| PVS02 | 2.749 | 0   | -0.008 | -0.974 | -1.157 | 0        | -2.139 |
+| PVS03 | 3.881 | 0   | -0.036 | -0.595 | 0      | -0.375   | -1.007 |
+| PVS04 | 1.599 | 0   | -0.003 | -0.203 | -2.320 | -0.763   | -3.288 |
+
+## Appendix II
+
+### Example of the deviation procedure with ITU-T P.1203 mode 3 (bitstream-based model) as a quality estimation model
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This appendix describes an example of the deviation procedure when ITU-T P.1203 mode 3 is used as a quality estimation model. Especially, PVSs used, input data specification and contribution values are described.
+
+#### Prepared PVSs
+
+In this example, the same PVSs as those of Appendix I are used. Thus, detailed information about the PVSs is omitted.
+
+#### Input data specifications
+
+The input data of this Recommendation is the adaptation set information, a sequence that is a history of selected media quality level during a media session, stalling information during a media session, and the final media session quality score. In addition to that, since ITU-T P.1203 mode 3 is a bitstream-based model, the bitstream information at each segment is used. The specifications of input data are in Table II.1, where the listed input data is based on ITU-T P.1203 mode 3, [ITU-T P.1203.2], [ITU-T P.1203.3].
+
+**Table II.1 – Input specifications**
+
+| Description                                             | Values                                               | Frequency         |
+|---------------------------------------------------------|------------------------------------------------------|-------------------|
+| The resolution of the image displayed to the user       | Number of pixels ( $W \times H$ ) in displayed video | Per media chunk   |
+| The device type on which the media is played            | "PC", "TV", "MO", "TA"                               | Per media chunk   |
+| Device display size                                     | Display size (diagonal in inches)                    | Per media chunk   |
+| Relative viewing distance in multiple of display height | Relative viewing distance                            | Per media chunk   |
+| Target audio bitrate                                    | Bitrate in kilobits per second                       | Per media segment |
+| Segment duration                                        | Duration in seconds                                  | Per media segment |
+| Audio frame number                                      | Integer, starting with 1                             | Per media segment |
+| Audio frame size                                        | Size of the frame in bytes                           | Per audio frame   |
+| Audio frame duration                                    | Duration in seconds                                  | Per audio frame   |
+| Audio codec                                             | One of: AAC-LC, AAC-HEv1, AAC-HEv2, AC3              | Per media segment |
+| Audio sampling frequency                                | In hertz                                             | Per media segment |
+| Number of audio channels                                | 2                                                    | Per media segment |
+| Audio bitstream                                         | Encoded audio bytes for the frame                    | Per audio frame   |
+| Video bitrate                                           | Bitrate in kilobits per second                       | Per media chunk   |
+
+**Table II.1 – Input specifications**
+
+| Description                             | Values                                                                                                                                                                                         | Frequency          |
+|-----------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| Video frame rate                        | Frame rate in frames per second                                                                                                                                                                | Per media chunk    |
+| Segment duration                        | Duration in seconds                                                                                                                                                                            | Per media chunk    |
+| Video encoding resolution               | Number of pixels ( $W \times H$ ) in transmitted video                                                                                                                                         | Per media chunk    |
+| Video codec and profile                 | ITU-T H.264-high                                                                                                                                                                               | Per media chunk    |
+| Video frame number                      | Integer, starting at 1, denoting the frame sequence number in encoding order                                                                                                                   | Per video frame    |
+| Video frame duration                    | Duration of the frame in seconds                                                                                                                                                               | Per video frame    |
+| Video frame size                        | The size of the encoded video frame in bytes                                                                                                                                                   | Per video frame    |
+| Type of each picture                    | "I"/"P"/"B"                                                                                                                                                                                    | Per video frame    |
+| Video bitstream                         | Encoded video bytes for the frame                                                                                                                                                              | Per video frame    |
+| Stalling or initial loading event start | The start time of the stalling event in seconds relative to the start of the original video clip, expressed in media time (not wall clock time)<br>NOTE – This is 0 for initial loading delay. | Per stalling event |
+| Event duration                          | The duration of the stalling event in seconds                                                                                                                                                  | Per stalling event |
+| Final media session quality score       | Scores provided per session and on a quality scale of 1 to 5                                                                                                                                   | Per session        |
+
+#### **Example of calculation steps**
+
+Most parts of the calculation step are the same as in Appendix I. Since the bitstream information is needed in ITU-T P.1203 mode 3, generation of the modified sequence is slightly different. Assume that the same  $N, x_j, S$  as in Appendix I and a sequence  $H$  as follows.
+
+$$H = [(QL4, b_{1,ql4}), (QL6, b_{2,ql6}), (QL2, b_{3,ql2}), (QL2, b_{4,ql2}), (QL7, b_{5,ql7})],$$
+
+where  $b_{j,qlk}$  represents a tuple of video frame size, type of each picture and quantization parameter values of media quality level  $k$  at segment  $j$  that are parsed from video bitstream. Then, the modified sequences become as follows.
+
+$$H' = [(QL7, b_{1,ql7}), (QL6, b_{2,ql6}), (QL2, b_{3,ql2}), (QL2, b_{4,ql2}), (QL7, b_{5,ql7})],$$
+
+$$H'' = [(QL7, b_{1,ql7}), (QL6, b_{2,ql6}), (QL7, b_{3,ql7}), (QL7, b_{4,ql7}), (QL7, b_{5,ql7})].$$
+
+Here,  $b_{j,ql7}$  is obtained as an input. Different from the metadata-based model, ITU-T P.1203 mode 0 in Appendix I, the media quality level and bitstream information at bold segments are replaced with the highest media quality level and bitstream information of the highest media quality level at those segments. Here, since the bitstream information of the highest quality level at each segment is placed at the streaming server, the contribution calculation is executed at the streaming server. The other steps are the same as those in Appendix I.
+
+#### **Calculation results**
+
+The calculated contribution values are listed in Table II.2, in which FQ means the final media session quality score of the corresponding PVS calculated by ITU-T P.1203 mode 3. QL7, QL6, QL4, QL2, and stalling columns mean the contribution value of each media quality level. The column total means the total value of the contribution value.
+
+Most calculated contribution values tend to be the same as those of ITU-T P.1203 mode 0 in Appendix I. However, since the quality estimation model and final quality media session quality score differ, the contribution values also differ from those of ITU-T P.1203 mode 0.
+
+In PVS01, since QL7, QL6, and QL2 are not selected and do not induce any quality degradation, the contribution value equals 0. Also, since stalling does not occur or induce any quality degradation, the contribution value equals 0. On the other hand, since QL4 was selected during the media session, it was  $-2.197$  points. In PVS02, QL6, QL4, and QL2 were selected. Thus, each media quality level reduced the FQ. In PVS03, since a stalling occurred, the contribution value of the stalling was  $-0.337$ . In PVS04, since several quality levels were selected, each quality level reduces the quality. Specifically, since stalling occurred twice and media quality level QL2 was selected many times in this PVS, the stalling and QL2 reduced the final media session quality score.
+
+**Table II.2 – Calculated results of contribution values for PVS01, PVS02, PVS03 and PVS04**
+
+|       | FQ    | QL7 | QL6    | QL4    | QL2    | Stalling | Total  |
+|-------|-------|-----|--------|--------|--------|----------|--------|
+| PVS01 | 2.631 | 0   | 0      | -2.197 | 0      | 0        | -2.197 |
+| PVS02 | 2.310 | 0   | -0.146 | -1.383 | -0.990 | 0        | -2.518 |
+| PVS03 | 3.192 | 0   | -0.200 | -1.099 | 0      | -0.337   | -1.636 |
+| PVS04 | 1.569 | 0   | -0.008 | -0.275 | -2.256 | -0.721   | -3.259 |
+
+## Appendix III
+
+### Example of the deviation procedure with [ITU-T P.1204.4] (pixel-based model) as a quality estimation model
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This appendix describes an example of the deviation procedure when [ITU-T P.1204.4] is used as a quality estimation model. Especially, the PVSs used, input data specification and contribution values are described.
+
+#### Prepared PVSs
+
+In this example, the same PVSs as those in Appendix I are used. Thus, detailed information about PVSs is omitted.
+
+#### Input data specifications
+
+The input data of this Recommendation is the adaptation set information, a sequence that is a history of selected media quality level during a media session, stalling information during a media session, and the final media session quality score. In addition to that, since [ITU-T P.1204.4] is a pixel-based model, the video pixel information at each segment is used. The input data are specified in Table III.1, where the listed input data is based on [ITU-T P.1204.4], [ITU-T P.1203.2], [ITU-T P.1203.3].
+
+**Table III.1 – Input specifications**
+
+| Description                                              | Values                                                                                                                                                                                         | Frequency          |
+|----------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| The resolution of the image displayed to the user        | Number of pixels ( $W \times H$ ) in displayed video                                                                                                                                           | Per media chunk    |
+| The device type on which the media is played             | "PC", "TV", "MO", "TA"                                                                                                                                                                         | Per media chunk    |
+| Device display size                                      | Display size (diagonal in inches)                                                                                                                                                              | Per media chunk    |
+| Relative viewing distance in multiples of display height | Relative viewing distance                                                                                                                                                                      | Per media chunk    |
+| Target audio bit-rate                                    | Bitrate in kilobits per second                                                                                                                                                                 | Per media segment  |
+| Segment duration                                         | Duration in seconds                                                                                                                                                                            | Per media segment  |
+| Audio codec                                              | One of: AAC-LC, AAC-HEv1, AAC-HEv2, AC3                                                                                                                                                        | Per media segment  |
+| Audio sampling frequency                                 | In hertz                                                                                                                                                                                       | Per media segment  |
+| Number of audio channels                                 | 2                                                                                                                                                                                              | Per media segment  |
+| Stalling or initial loading event start                  | The start time of the stalling event in seconds relative to the start of the original video clip, expressed in media time (not wall clock time)<br>NOTE – This is 0 for initial loading delay. | Per stalling event |
+
+**Table III.1 – Input specifications**
+
+| Description                       | Values                                                                                                                                                                                                                                                                                                                                                                                | Frequency          |
+|-----------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| Event duration                    | The duration of the stalling event in seconds                                                                                                                                                                                                                                                                                                                                         | Per stalling event |
+| Degraded video                    | The raw pixels (YUV file including metadata required for parsing; width, height, frame rate and pixel format) of the processed video, i.e., the video decoded and upscaled to display resolution without buffering or stalling. The frame information in degraded video and reference video is synchronized, i.e., no frame misalignments are present                                 | Per media chunk    |
+| Reference video information       | The reference-side information extraction module takes as input the reference video and outputs the side information file.<br>The reference model side channel bandwidth limit is 256 kbit/s. Thus, the side information of the reference model for a video sequence $v$ is stored in a file with size at most $256/8 * t_v$ kB, where $t_v$ is the duration of video $v$ in seconds. | Per media chunk    |
+| Final media session quality score | Scores provided per session and on a quality scale of 1 to 5                                                                                                                                                                                                                                                                                                                          | Per session        |
+
+#### **Example of calculation steps**
+
+Most parts of the calculation step are the same as those in Appendix I. Since the pixel information is needed in [ITU-T P.1204.4], a sequence and modified sequences are slightly different. Assume the same  $N, x_j, S, H$  as in Appendix I. In addition to that in the pixel-based model, the pixel information of that sequence  $H$ ,
+
+$$H = [(QL4, p_{1,q14}), (QL6, p_{2,q16}), (QL2, p_{3,q12}), (QL2, p_{4,q12}), (QL7, p_{5,q17})],$$
+
+where  $p_{j,q1k}$  represents the degraded video pixel information of media quality level  $k$  at segment  $j$ . Then, the modified sequences become as follows.
+
+$$H' = [(QL7, p_{1,q17}), (QL6, p_2), (QL2, p_3), (QL2, p_4), (QL7, p_5)],$$
+
+$$H'' = [(QL7, p_{1,q17}), (QL6, p_2), (QL7, p_{3,q17}), (QL7, p_{4,q17}), (QL7, p_5)].$$
+
+Also, when the final media session quality score of  $H, H'$  and  $H''$  is calculated using [ITU-T P.1204.4], reference video pixel information is used.
+
+Here, since the pixel information of the highest media quality level at each segment is placed at the streaming server, the contribution calculation is executed at the streaming server. The other steps are the same as those in Appendix I.
+
+#### **Calculation results**
+
+Table III.2 shows the calculated contribution values. In Table III.2, FQ means the final media session quality score of the corresponding PVS calculated by [ITU-T P.1204.4]. QL7, QL6, QL4, QL2, and stalling columns mean the contribution value of each media quality level. The column total means the total value of the contribution value.
+
+Most calculated contribution values tend to be the same as those of ITU-T P.1203 mode 0 in Appendix I. However, since the quality estimation model and final quality media session quality score differ, the contribution values also differ from those of ITU-T P.1203 mode 0.
+
+In PVS01, since QL7, QL6, and QL2 are not selected and do not induce any quality degradation, the contribution value equals 0. Also, since stalling does not occur or induce any quality degradation, the
+
+contribution value equals 0. On the other hand, since QL4 was selected during a media session, it was the  $-0.965$  points. In PVS02, QL6, QL4 and QL2 were selected. Thus, each media quality level reduced the FQ. In PVS03, since stalling occurred, its contribution value was  $-0.051$ . In PVS04, since several quality levels were selected, each quality level reduced the quality. Specifically, since stalling occurred twice and media quality level QL2 was selected many times in this PVS, the stalling and QL2 reduced the final media session quality score.
+
+**Table III.2 – Calculated results of contribution values for PVS01, PVS02, PVS03, and PVS04**
+
+|       | FQ    | QL7 | QL6      | QL4      | QL2      | Stalling | Total    |
+|-------|-------|-----|----------|----------|----------|----------|----------|
+| PVS01 | 3.442 | 0   | 0        | $-0.965$ | 0        | 0        | $-0.965$ |
+| PVS02 | 3.243 | 0   | $-0.064$ | $-0.511$ | $-0.590$ | 0        | $-1.164$ |
+| PVS03 | 3.775 | 0   | $-0.225$ | $-0.375$ | 0        | $-0.051$ | $-0.632$ |
+| PVS04 | 1.871 | 0   | $-0.002$ | $-0.040$ | $-1.675$ | $-0.818$ | $-2.536$ |
+
+## Bibliography
+
+- [b-ITU-T H.264] Recommendation ITU-T H.264 (2021), *Advanced video coding for generic audiovisual services*.
+- [b-ITU-T H.265] Recommendation ITU-T H.265 (2023), *High efficiency video coding*.
+- [b-ITU-T P.10] Recommendation ITU-T P.10/G.100 (2017), *Vocabulary for performance, quality of service and quality of experience*.
+- [b-Robitza] Robitza, W., Göring, S., Raake, A., Lindegren, D., Heikkilä, G., Gustafsson, J., List, P., Feiten, B., Wüstenhagen, U., Garcia, M.-N., Yamagishi, K., Broom, S. (2018). HTTP adaptive streaming QoE estimation with ITU-T Rec. P.1203 – Open databases and software. In: *9th ACM Multimedia Systems Conference*, Amsterdam, 2018-06-12/15, pp. 466-471. New York, NY: Association for Computing Machinery. <https://doi.org/10.1145/3204949.3208124>
+- [b-Shapley] Shapley, L.S. (1953). A value for  $n$ -person games. In: Kuhn, H., Tucker, A., editors. *Contributions to the theory of games*, vol. 2, pp. 307–317. Princeton, NJ: Princeton University Press. <https://doi.org/10.1515/9781400881970-018>
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | Tariff and accounting principles and international telecommunication/ICT economic and policy issues                                                       |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                                                       |
+| Series Q        | Switching and signalling, and associated measurements and tests                                                                                           |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

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@@ -0,0 +1,2007 @@
+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.1302**
+
+(10/2014)
+
+SERIES P: TERMINALS AND SUBJECTIVE AND  
+OBJECTIVE ASSESSMENT METHODS
+
+Telemeeting assessment
+
+---
+
+**Subjective method for simulated conversation  
+tests addressing speech and audio-visual call  
+quality**
+
+Recommendation ITU-T P.1302
+
+# ITU-T P-SERIES RECOMMENDATIONS
+
+## TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS
+
+|                                                                                                  |               |               |
+|--------------------------------------------------------------------------------------------------|---------------|---------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality    | Series        | P.10          |
+| Voice terminal characteristics                                                                   | Series        | P.30          |
+|                                                                                                  |               | P.300         |
+| Reference systems                                                                                | Series        | P.40          |
+| Objective measuring apparatus                                                                    | Series        | P.50          |
+|                                                                                                  |               | P.500         |
+| Objective electro-acoustical measurements                                                        | Series        | P.60          |
+| Measurements related to speech loudness                                                          | Series        | P.70          |
+| Methods for objective and subjective assessment of speech quality                                | Series        | P.80          |
+|                                                                                                  |               | P.800         |
+| Audiovisual quality in multimedia services                                                       | Series        | P.900         |
+| Transmission performance and QoS aspects of IP end-points                                        | Series        | P.1000        |
+| Communications involving vehicles                                                                | Series        | P.1100        |
+| Models and tools for quality assessment of streamed media                                        | Series        | P.1200        |
+| <b>Telemeeting assessment</b>                                                                    | <b>Series</b> | <b>P.1300</b> |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                | Series        | P.1400        |
+| Methods for objective and subjective assessment of quality of services other than voice services | Series        | P.1500        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+## Recommendation ITU-T P.1302
+
+# Subjective method for simulated conversation tests addressing speech and audio-visual call quality
+
+## Summary
+
+Recommendation ITU-T P.1302 describes a subjective method for assessing the quality of simulated speech or audio-visual telephony calls with time-varying transmission conditions. Simulated calls consist of several stretches of speech or audio-visual material which are ordered in a logical sequence, according to a storyline defined by a scenario. After each stretch, test participants have to answer a content-related question, and they have to rate the overall quality of the call at the end of the entire sequence. The method is meant as a complement to standard listening-only or conversational tests, provoking a fixed structure in the material to be judged, while maintain a more-or-less conversational attention focus of the test participants.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T P.1302   | 2014-10-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/12325">11.1002/1000/12325</a> |
+
+## Keywords
+
+Audio-visual quality, call quality, conversation quality, speech quality, subjective methodology.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2015
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                                                                         | Page |
+|-------------------------------------------------------------------------------------------------------------------------|------|
+| 1 Scope.....                                                                                                            | 1    |
+| 2 References.....                                                                                                       | 2    |
+| 3 Definitions .....                                                                                                     | 2    |
+| 3.1 Terms defined elsewhere .....                                                                                       | 2    |
+| 3.2 Terms defined in this Recommendation.....                                                                           | 2    |
+| 4 Abbreviations and acronyms .....                                                                                      | 2    |
+| 5 Conventions .....                                                                                                     | 3    |
+| 6 Subjective test methodology.....                                                                                      | 3    |
+| 6.1 Simulated conversation test addressing speech quality.....                                                          | 3    |
+| 6.2 Simulated conversation tests addressing audio-visual quality .....                                                  | 4    |
+| 6.3 Features of the text material .....                                                                                 | 4    |
+| 6.4 Pre-processing of the short segments .....                                                                          | 4    |
+| 6.5 Questions and post-screening of participants .....                                                                  | 4    |
+| Appendix I – Exemplary scenarios for simulated conversations addressing speech quality<br>and audio-visual quality..... | 6    |
+| Appendix II – Exemplary questions and answers to the scenarios from Appendix I .....                                    | 11   |
+| Appendix III.....                                                                                                       | 41   |
+| Bibliography.....                                                                                                       | 42   |
+
+
+
+# Subjective method for simulated conversation tests addressing speech and audio-visual call quality
+
+## 1 Scope
+
+In this Recommendation, a subjective test procedure is described which is able to assess the quality of speech or audio-visual telephone calls, the so-called "call quality". In contrast to standard listening-only tests as described in [ITU-T P.800], call quality refers to the experience of a user during a typically 1-2 min long call. Such experiences are commonly addressed in conversation tests as described in [ITU-T P.800] and [ITU-T P.805], however real conversation tests commonly lack analytical power, because naïve test participants have to concentrate mainly on the flow of the conversation, and are unable to rate instances of good or bad quality. In turn, methods for the continuous assessment of quality as described in [ITU-T P.880] do not put the listener in a situation which is comparable to a conversation.
+
+In order to circumvent this problem, ETSI has developed a method for "simulated conversation tests" in [b-TR 102 506], which has been adopted in this Recommendation and extended to audio-visual telephony. Simulated conversations consist of a number of short (8-12 s) stretches of speech, typically five, which are presented to the listening or listening-and-viewing test participants, and which follow a logical storyline. After each stretch of speech, the test participant has to answer a short content-related question, e.g., in terms of an answer to a multiple-choice question. Following the answer, the next stretch of speech or audio-visual material is presented, followed by the next question, and so forth until the end of the logical sequence is reached. Upon the end of the sequence, the test participant has to judge the perceived quality of the entire call on a standard (typically five-point ACR according to [ITU-T P.800] and [ITU-T P.911]) quality scale. Those multiple-choice questions may refer to information transmitted via the audio, video or audio-visual modality.
+
+Quality of short segments can either be predicted with subjective methods, e.g., [ITU-T P.911] for audiovisual segments or [ITU-T P.800] for speech segments, or can be assessed with instrumental models like [ITU-T P.863] or [ITU-T J.341], in order to analyse the relationship between the quality of individual samples and the quality of the entire call as assessed with this Recommendation.
+
+The method is not intended to replace listening-only tests according to [ITU-T P.800] or listening-and-viewing tests according to [ITU-T P.911], or speech conversation tests according to [ITU-T P.800] or audio-visual conversation tests according to [ITU-T P.920]. Rather, it is recommended to make use of the appropriate method as follows:
+
+- In case that the listening-only or listening-and-viewing quality is of interest and that the quality is considered to be constant throughout the duration of a speech-only or audio-visual call, the method according to [ITU-T P.800] or [ITU-T P.911] should be used. [ITU-T P.800] is, however, not recommended for longer durations.<sup>1</sup>
+- In case that the listening-and-viewing quality is of interest and that the quality is considered not to be constant throughout the duration of a speech-only or audio-visual call, the present method should be used; in contrast to the task of rating overall quality in [ITU-T P.880] it addresses also audio-visual material and aims at establishing a more valid situation by introducing active participation of the participants.
+
+---
+
+<sup>1</sup> A validation within ITU-T SG12 has revealed no significant differences between the results of a [ITU-T P.911] test and a test according to the present simulated conversation test method results, for a limited number of constant audio, video or audio-visual quality degradations.
+
+- In case that conversational quality which may be impacted by conversation-specific degradations like echo or delay is of interest, the method according to [ITU-T P.800], [ITU-T P.805] or [ITU-T P.920] should be used.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+[ITU-T J.341] Recommendation ITU-T J.341 (2011), *Objective perceptual multimedia video quality measurement of HDTV for digital cable television in the presence of a full reference*.
+
+[ITU-T P.10] Recommendation ITU-T P.10/G.100 (2006), *Vocabulary for performance and quality of service*.
+
+[ITU-T P.800] Recommendation ITU-T P.800 (1996), *Methods for subjective determination of transmission quality*.
+
+[ITU-T P.805] Recommendation ITU-T P.805 (2007), *Subjective evaluation of conversational quality*.
+
+[ITU-T P.863] Recommendation ITU-T P.863 (2011), *Perceptual objective listening quality assessment*.
+
+[ITU-T P.880] Recommendation ITU-T P.880 (2004), *Continuous evaluation of time-varying speech quality*.
+
+[ITU-T P.911] Recommendation ITU-T P.911 (1998), *Subjective audiovisual quality assessment methods for multimedia applications*.
+
+[ITU-T P.920] Recommendation ITU-T P.920 (2000), *Interactive test methods for audiovisual communications*.
+
+# 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 conversational quality** [ITU-T P.10]: Quality with which a bi- or multidirectional conversation is perceived by a communication partner.
+
+**3.1.2 conversational speech quality** [ITU-T P.10]: Speech quality as experienced in a bi- or multidirectional conversation.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 call quality**: Listening quality as perceived by a user at the end of a conversational call.
+
+## 4 Abbreviations and acronyms
+
+None.
+
+## 5 Conventions
+
+None.
+
+## 6 Subjective test methodology
+
+The characteristics of this methodology are as follows:
+
+- By orally answering the questions related to each stretch of speech, test participants should be made to be involved in a conversation; nevertheless, the situation is a pure listening or listening-and viewing one, allowing the test participants to concentrate more on the form of the media than it would be possible in a real conversation.
+- The conversation is highly structured; in fact, it consists of short samples as they are used in standard listening-only or watching and listening-only tests according to [ITU-T P.800] and [ITU-T P.911].
+
+Details of the methodology are described in the following paragraphs; the method is thus particularly tailored to situations where the quality varies over the time of a call.
+
+### 6.1 Simulated conversation test addressing speech quality
+
+A typical telephony situation is a dialogue between two persons in which both interlocutors have a certain amount of speaking and listening activity. Thus, the test situation is divided into parts with listening-only activity and parts with speaking activity. It is supposed that both participants in a conversation are interested in the conversation topic; in the test, this is realized by the test participant being asked for certain aspects of the content, thus to direct the focus of attention to the content of the presented speech stimuli, as it would be in a natural conversation situation.
+
+In order to ensure the ecological validity of the test, typical contents of telephone conversations are chosen (e.g., request for a rental car, discussing the furniture in a room). The realization of such a simulated conversation consists of a series of shorter "utterances", which have a pause between them for interaction but are connected logically with regard to the content of the presentation. Instead of the own speech activity as a reply, an artificial content-directed task is to be done by the test participants. For example, test participants have to answer a question related to the content of the past stimulus, which can be done by keyword spotting.
+
+The speech samples used for the test should address topics like in a natural telephone situation. A simulated conversation consists of five samples of approximately 8-12 seconds and is constructed in such a way that four breaks are possible. After the fifth test stimulus, the participant is asked for an assessment for the overall call quality of the simulated call, instead of the content-related question. The questions asked to the participants after each sample of the simulated conversations and the corresponding answer options are presented on paper or on a computer screen after each sample. For each sample, a set of different questions is recommended in order to prevent test participants from memorizing the answers. The position of the right answer should also be randomly changed in order to avoid participants answering mechanically. The number of multiple choice answer options may vary between three and five. Simulated calls should be constructed for at least four speakers balanced in gender and comprising different scene backgrounds and conversation topics.
+
+![Schematic representation of the simulated conversation structure](99bae07626f60f9ede10e2e387ef7051_img.jpg)
+
+The diagram illustrates the temporal structure of a simulated conversation. It consists of a horizontal bar divided into nine alternating segments: five dark grey segments and four white segments. Above the first dark grey segment is the label "Pre-recorded processed segment" with a downward arrow. Above the first white segment is the label "Pause with content-oriented task" with a downward arrow. Above the final dark grey segment is the label "Quality assessment" with a rightward arrow.
+
+Schematic representation of the simulated conversation structure
+
+**Figure 1 – Schematic representation of the simulated conversation structure**
+
+Figure 1 shows an exemplary structure of such a simulated conversation, using samples of 12 second length. The used speech material consists of five speech parts (samples), which correspond to the utterances of one party. After a 12 seconds speech sample there is a 12 seconds pause during which the test person had to perform a content regarding task. At the end of the sequence a score for the Call Quality is solicited from the test participants using an absolute category rating scale as described in [ITU-T P.800]. Thus, the overall length of the simulated conversation is approx. 120 seconds, including the answering and quality-rating phases.
+
+### 6.2 Simulated conversation tests addressing audio-visual quality
+
+Similar to the methodology for speech-only call quality, a simulated videotelephony conversation is constructed as a set of five consecutive samples of short video clips. The samples are linked by the storyline. Participants are asked to watch each clip and then to verbally answer a question about the audiovisual content of the clip. The question could be related to the auditory content only, to the video content only, or to the audiovisual one, that is to say, a question that could be answered by using clues from both visual and auditory channels. The questions asked to the participants after each sample of the simulated conversations and the corresponding answer options are presented on a computer screen after each sample. The number of multiple choice answer options may vary between three and five. For each sample, a set of different questions is recommended in order to prevent test participants from memorizing the answers. The position of the right answer should also be randomly changed in order to avoid participants answering mechanically.
+
+Audiovisual clips should be composed of at least four speakers balanced in gender, comprising different scene backgrounds and conversation topics. The clips should involve the video channel by the means of visual cues (i.e., showing objects to the camera, pointing dates on a wall calendar, body gestures), so that the test participants have to pay attention to the video channel. The video clips and the time period allowed to answer each question should have approximately the same length, leading to a total duration of 10 times the stimulus length or 8-12 seconds. At the end of each simulated conversation, test participants have to rate the audiovisual quality of the entire dialog using a standard overall quality scale, as recommended in [ITU-T P.911].
+
+### 6.3 Features of the text material
+
+When creating text material for recording the short stimuli, a whole scenario should be decided upon first, so each stimulus (utterance) represents an authentic sequel of the previous stimuli. Validated so far have been scenarios using a narrative form, i.e., without implying interlocutor's verbal action. In that way, listeners/raters are not confused when just answering questions instead of reacting on the stimuli, and two short utterances can be combined to one longer stimulus, if desired.
+
+Also, each utterance should provide more than one important piece of information. That allows for more questions, but also prohibits a too easy listening task.
+
+For the audio-visual tests, information should be spread on the two modalities, and accordingly, questions should be drafted explicitly addressing either audio or video transmitted information. See Appendices I and II for examples.
+
+### 6.4 Pre-processing of the short segments
+
+The original samples should be processed to obtain transmission quality as needed. As this method aims at time-varying transmission characteristics, changes in transmission characteristics can be induced between or within the short segments. Example profiles already used are illustrated in Appendix III.
+
+### 6.5 Questions and post-screening of participants
+
+During the development of this method, the participant's answers have been recorded. But it has been shown that noting errors during a session was easily manageable by the instructor to automatically
+
+calculate the error rates. The purpose of this post-evaluation screening is to find possible outliers, i.e., participants who obviously did not concentrate sufficiently on the content or all modalities provided in order to give valid ratings of call quality. As with strongly degraded transmission, errors may occur independent of concentration, it is suggested to define the exclusion criterion depending on the performance of subjects throughout the test. The alternative answers should be displayed on a screen without alpha-numerical labels to prevent participants just referring to these labels, but uttering (at least parts of) the answer.
+
+Furthermore, while questions concerning audio, video or audio-visual content can be used, without observing major difference in the perceived quality of the samples, a combination of audio and video content questions is preferred in order to prevent priming towards one modality.
+
+## Appendix I
+
+### Exemplary scenarios for simulated conversations addressing speech quality and audio-visual quality
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This Recommendation is based on experiments, which were originally partially carried out in German. Because of this, the original German scenario descriptions are added here for completeness. In principle, experiments following this procedure should be carried out in the language under consideration, using scenario description in that language. A re-translation of the English scenario descriptions into German might provide slightly different results when compared to the original experiments.
+
+The following scenarios are designed to combine sentences (e.g., two) to one single stimulus.
+
+### Scenario 1: Scheduling medical treatment
+
+- 1) Hello, this is Markus Lehmann. I would like to make an appointment concerning the treatment of my back complaint as discussed. [point to your back]
+- 2) We had agreed on six weeks with two radiation sessions each. I would like to start the treatment now. [go to the wall calendar]
+- 3) In the morning I am always busy. But on Tuesdays and on Thursdays would be fine. [point to Tuesday and Thursday on the calendar]
+- 4) There is no way to come on Wednesdays, as I attend a language course at these days. I would like best to have regular appointments. [point to a huge blocker on Wednesday]
+- 5) Besides, do you think that additional gymnastic exercises could decrease my afflictions in the long run? [do some exercises]
+- 6) I was thinking about an introduction under the tutelage of a physiotherapist. Maybe, that could be a good complement to the radiation. [do some more exercises]
+- 7) I hope the treatment costs will be fully paid by the health insurance. For this treatment, however, I do not know for certain.
+- 8) Yesterday, I read in a newspaper once more about the approval of new austerity plan, mainly concerning the amount of assumption of costs. [show a newspaper]
+- 9) Additionally, I would like to make an appointment with your partner in the group practice, the dentist Dr Kollwitz.
+- 10) The date can even be next month. I would actually prefer it next month, as I am very busy this one. [point to the end of the month on a calendar]
+
+(German)
+
+- 1) Guten Tag, hier ist Marcus Lehmann. Ich hätte gerne einen Termin bei Ihnen wegen der besprochenen Behandlung meiner Rückenbeschwerden. [Zeigt auf seinen Rücken]
+- 2) Wir hatten abgestimmt, dass ich sechs Wochen lang je zwei Bestrahlungen bekommen soll. Ich würde die Behandlung nun gerne beginnen. [Geht zum Wandkalender]
+- 3) Auf keinen Fall kann ich vormittags. Dienstags und donnerstags wäre es mir sehr recht. [zeigt am Wandkalender auf Dienstag und Donnerstag]
+- 4) Mittwoch ist bei mir unmöglich, da ich an diesem Tag einen Sprachkurs besuche. Am liebsten wären mir regelmäßige Termine. [Zeigt am Wandkalender auf Mittwoch, wo ein großer Blocker steht]
+
+- 5) Außerdem möchte ich Ihre Meinung dazu hören, ob zusätzliche Gymnastik meine Beschwerden vielleicht langfristig verringern könnte. [Macht etwas Gymnastik in die Kamera]
+- 6) Ich denke an eine Einführung unter Anleitung einer Krankengymnastin. Vielleicht ist das eine gute Ergänzung zu den Bestrahlungen. [Macht weiterhin Gymnastik]
+- 7) Ich hoffe, die Kosten der Behandlung werden komplett von der Krankenkasse übernommen. Allerdings weiß ich nicht, ob es auch meine Behandlung betrifft.
+- 8) Gestern habe ich wieder in der Zeitung gelesen, dass neue Sparpläne verabschiedet worden sind, die hauptsächlich die Höhe der Eigenbeteiligung betreffen. [Hält eine Zeitung in die Kamera]
+- 9) Zusätzlich möchte ich noch einen Gesprächstermin mit Ihrer Praxispartnerin, der Zahnärztin Dr. Kollwitz, vereinbaren.
+- 10) Der Termin kann ruhig erst im nächsten Monat liegen. Das ist mir sogar lieber, da ich diesen Monat sehr beschäftigt bin. [Zeigt am Wandkalender das Ende des Monats]
+
+### **Scenario 2: Car Rental**
+
+- 1) Hello, this is Maria Eibig and I would like to rent a car. [grab a catalogue and show it]
+- 2) A bigger estate car would be sufficient. But if a van is cheaper I would also take one of those.
+- 3) I would prefer midweek, that is Wednesday. At that day I would need the car close to half past 8 pm. [show a picture with an estate car]
+- 4) But if you offer a special rate for the weekend, I would do my transport then. [point to a wall calendar behind you]
+- 5) For me it is important to take out an assurance for the car. I would also take the small trolley as per your offer. [point to the weekend on the calendar]
+- 6) Additionally, I would like to have a mileage allowance for more than 500 kilometres and blankets as packaging material.
+- 7) I would like to pay with my credit card. My customer number is 24 12. [show your credit card]
+- 8) Last time I rented a Golf. That was beginning of last month. [point at the begin of the month on the calendar]
+- 9) That time I returned the car fully fuelled. This time I will not manage to do so, as I will come back not until the evening. [shake your head]
+- 10) I will then bring the car directly to your car park and return the following morning to do the billing. [point to a certain position on a map]
+
+(German)
+
+- 1) Guten Tag, hier ist Maria Eibig und ich möchte bei Ihnen gern einen Wagen reservieren. [Hole die Broschüre eines Autoverleihers heraus und halte sie in die Kamera]
+- 2) Ein größerer Kombi reicht mir dafür aus, wenn ein Kleintransporter preiswerter ist, würde ich auch diesen nehmen. [Zeige ein Bild mit einem Kombi]
+- 3) Mir wäre Mitte der Woche, also Mittwoch, am liebsten. Da würde ich den Wagen gegen zwanzig Uhr dreißig benötigen. [Zeige dabei auf einen Wandkalender hinter Dir]
+- 4) Wenn sie einen Spezialtarif am Wochenende anbieten, würde ich den Transport auch am Wochenende machen. [Zeige am Wandkalender auf das Wochenende]
+- 5) Wichtig ist mir noch der Abschluss einer Versicherung für das Fahrzeug. Den kleinen Rollwagen aus Ihrem Programm nehme ich ebenfalls mit.
+
+- 6) Außerdem brauche ich eine Kilometerpauschale von über 500 Kilometern und Decken als Verpackungsmaterial.
+- 7) Ich habe eine Kreditkarte mit der ich den Wagen bezahlen möchte. Meine Kundennummer ist 24 12. [Zeige die Kreditkarte in die Kamera]
+- 8) Zuletzt hatte ich mir einen Golf geliehen. Das war am Anfang des letzten Monats. [Zeige im Kalender auf den Monatsbeginn]
+- 9) Das letzte Mal hatte ich den Wagen vollgetankt zurückgegeben. Diesmal werde ich das wohl nicht schaffen, da ich erst abends zurückkomme. [Kopf schütteln]
+- 10) Ich fahre den Wagen dann gleich auf Ihren Firmenparkplatz und komme dann am darauffolgenden Morgen zu Ihnen zur Abrechnung. [Zeige auf einen Punkt auf einer Karte]
+
+### **Scenario 3: Kitchen purchase order**
+
+- 1) Hello. I would like to order a built-in kitchen. Would it be possible to talk to Mrs Müller? [show a catalogue]
+- 2) She consulted me in your salesrooms and we loosely agreed upon calling her until Wednesday.
+- 3) I decided on the version in light grey. Giving a thought to it, a white kitchen appeared to be too cold to me. [show a picture of a light grey kitchen]
+- 4) Furthermore, I would like to have the doorknobs with the lozenge shape, as the round shape is a little bit too small in my opinion. [show a detailed picture of the doorknob]
+- 5) Concerning the sink I consider taking a single unit. Thereby there is still space for a dishwasher. [show a picture of a sink]
+- 6) I decided on the small dishwasher from the brand "Futura". Do you have one of these on offer? [show a picture of a small washer]
+- 7) I suppose this washer provides aqua-stop. If not, I would rather take the next bigger model. [point to a "Aqua-Stop" label; alternatively change to "energy label"]
+- 8) I am not decided yet on the cooker. I would like best to have one with glass-ceramic top and sensor circuitry. [point to top in the catalogue]
+- 9) I am fine with the table. I would like to have one in the size of 100x160 cm. [show roughly the size with your hands in the air]
+- 10) If I understood the catalogue correctly, it can be extended to the length of 200 cm. [show the extended size]
+
+(German)
+
+- 1) Hallo, ich möchte bei Ihnen gerne eine Einbauküche bestellen. Ist es möglich, dass ich mit Frau Müller spreche? [Zeigt eine Küchenbroschüre in die Kamera]
+- 2) Sie hat mich in Ihren Verkaufsräumen beraten und ich hatte grob mit Ihr abgesprochen, dass ich mich bis Mittwoch bei Ihr melden werde.
+- 3) Ich habe mich für die Variante in Hellgrau entschieden. Eine weiße Küche kam mir bei längerer Überlegung doch zu kalt vor. [Zeigt das Bild einer hellgrauen Küche in die Kamera]
+- 4) Außerdem möchte ich alle Türknäufe in Rautenform, die Runden sind mir doch ein wenig zu klein. [Zeigt das Detailbild von Türknäufen]
+- 5) Für die Spüle habe ich mir überlegt, doch nur ein Becken zu nehmen. Dadurch bleibt Platz für eine Spülmaschine. [Zeigt das Bild eines Spülbeckens]
+- 6) Ich habe mich für die schmale Maschine der Firma Futura entschieden. Haben Sie so ein Gerät im Angebot? [Zeige eine schmale Maschine im Katalog]
+
+- 7) Ich nehme an, dass diese Maschine über einen Aqua-Stop verfügt. Falls nicht möchte ich lieber das nächst größere Modell. [Zeige Aqua-Stop Label im Katalog; alternativ ändern in Energiesparlabel]
+- 8) Bei dem Herd bin ich mir noch nicht sicher. Am liebsten hätte ich ein Gerät mit Glaskeramik Kochfeldern und Sensorschaltung. [zeige Kochfeld im Katalog]
+- 9) Der Tisch gefällt mir gut. Ich hätte ihn gerne in der Größe 100 x 100 cm. [Zeigt die gewünschte Größe in der Luft]
+- 10) Wenn ich den Prospekt richtig verstehe lässt er sich auf eine Länge von 150 cm vergrößern. [Zeigt eine Vergrößerung in die Luft]
+
+#### **Alternative Scenario 4: Birthday party**
+
+- 1) Hi Jan. Last Saturday I went to Peter's birthday party. It was really great! [please wave and make an inviting facial expression]
+- 2) There I met an old acquaintance. Here is a photo of our old friends with me. This is Stefan, Linda, and Markus. [show the photo and point to Stefan, Linda, and Markus each at a time]
+- 3) After dinner a band arrived at the party and played music. I believe the guests really enjoyed it. Spirits were running high. Here is a shot. [show photo of people dancing in front of a band]
+- 4) Do you remember Julia from our time at school? The two of us danced in the garden and she even taught me a break-dance move. Have a look. [show a photo of Julia and do a dance move]
+- 5) At midnight we all gathered around a big cake to sing "happy birthday". The cake was made by Peter's mother. It was marvellous.
+- 6) Before having the cake Peter received his presents. He got a drum set jointly from his parents and friends. Here is a photo. [show a picture from a drum set]
+- 7) I talked with some of our old friends about the good old days at school and told each other funny story from back then. We laughed quite a bit. [smile and laugh]
+- 8) When Peter's brother had to go to sleep, we sang a children's song, so he could fall asleep. [sing a children's song]
+- 9) Then, Peter's parents told me details about their journey to Asia. They also told me how to use eating sticks. Like this. [show using eating sticks]
+- 10) I would like to meet you this week eventually and talk a while. I wish you well. Goodbye. [wave goodbye and smile]
+
+(German)
+
+- 1) Hallo Jan! Ich war letzten Samstag auf der Geburtstagsparty von Peter. Da war es wirklich super! [bitte winke und mache ein einladendes Gesicht]
+- 2) Ich habe dort viele alte Bekannte getroffen. Da ist ein Foto von mir und unseren alten Freunden. Da ist Stefan, Linda und Markus. [zeige das Foto und zeige jeweils auf Stefan, Linda und Markus]
+- 3) Nach dem Essen kam noch eine Band auf die Party und hat Musik gemacht. Ich glaube, die Gäste fanden das richtig gut. Die Stimmung war ziemlich ausgelassen. Da ist ein Foto. [zeige ein Bild auf dem viele Leute vor einer Band tanzen]
+- 4) Erinnerst Du Dich noch an Julia aus der Schulzeit? Wie haben zusammen im Garten getanzt und sie hat mir sogar ein Break-Dance Move gezeigt. Schau mal! [zeige das Bild von Julia und mache eine Tanzbewegung]
+- 5) Um Mitternacht haben wir uns dann alle um einen großen Kuchen versammelt, um Happy-Birthday zu singen. Den Kuchen hat Peters Mutter gemacht, der war fantastisch. [zeige ein Bild vom Kuchen.]
+
+- 6) Vor dem Kuchenessen haben wir dann alle Peter seine Geschenke gegeben. Er hat ein Drumset gemeinsam von seinen Eltern und seinen Freunden bekommen. Hier ist das Foto. [zeige ein Bild vom Schlagzeug]
+- 7) Einige alte Freunde und ich haben uns über die gute alte Zeit an der Schule gesprochen und uns lustige Geschichten von damals erzählt. Wir haben ziemlich viel gelacht. [Lächeln und lachen]
+- 8) Als Peters Bruder ins Bett musste, haben wir ein Kinderlied gesungen, damit er einschläft. [singe ein Kinderlied]
+- 9) Peters Eltern haben mir noch Genaueres von ihrer Reise nach Asien erzählt und mir gezeigt, wie man mit Stäbchen isst! So ungefähr. [zeige die Stäbchen]
+- 10) Ich hoffe, wir können uns noch in dieser Woche mal treffen und etwas länger reden. Mach es gut, Tschüss! [winke zum Abschied und zeige ein natürliches Lächeln]
+
+## Appendix II
+
+## Exemplary questions and answers to the scenarios from Appendix I
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Questions are separated in those concerning information from the audio (A), video (V) or both channels (AV). These should be mixed for the AV condition. The order of the answers should be randomized. Correct answers are bold. Subject making errors frequently should be excluded from analysis. Gender of the speaker has to be adjusted. If two subsequent sentences are presented a one stimulus, the short answers can be extended up to whole sentences.
+
+### Scenario 1: Scheduling medical treatment
+
+#### 1.1A Why does the patient call?
+
+- a) he wants to speak to an employee
+- b) he misdialled
+- c) **he wants to get an appointment for a treatment**
+- d) he needs a prescription
+- e) he wants a vaccination
+
+#### 1.2AV What medical condition does he have?
+
+- a) toothache
+- b) **backache**
+- c) twisted ankle
+- d) he complaints about the treatment
+- e) gnawing headache
+
+#### 1.3V Which body part does the patient show?
+
+- a) **back**
+- b) shoulder
+- c) wrist
+- d) elbow
+- e) neck
+
+#### 2.1A What does the patient want to do with respect to the treatment?
+
+- a) **start it**
+- b) pay for it
+- c) stop it
+- d) interrupt it
+- e) change it
+
+#### 2.2A How long should the treatment be?
+
+- a) 1 week
+- b) 1 year
+- c) **6 weeks**
+- d) 2 weeks
+- e) 5 days
+
+**2.3A What kind of treatment is she supposed to get?**
+
+- a) pills
+- b) radiation**
+- c) infusions
+
+**2.4V Which date is shown on the calendar? (correct answer depends of material preparation)**
+
+- a) Monday, 15th
+- b) Tuesday, 16th
+- c) Wednesday, 17th
+- d) Thursday, 18th
+- e) Friday, 19th
+
+**3.1AV Which days does the patient prefer?**
+
+- a) Wednesdays only
+- b) work days
+- c) Tuesdays and Thursdays**
+- d) 13th and 14th of February
+- e) weekends
+
+**3.2A When can he not manage to come?**
+
+- a) weekends
+- b) mornings**
+- c) next week
+- d) on foul weather
+- e) in the evening
+
+**3.3V Which days are already marked in the calendar?**
+
+- a) Monday and Tuesday
+- b) Tuesday and Thursday
+- c) Thursday and Saturday
+- d) Wednesday**
+
+**4.1A Why does he not want to come on Wednesdays?**
+
+- a) appointment with a dentist
+- b) soccer training
+- c) language course**
+- d) taking care of his grandmother
+- e) working as newspaper carrier
+
+**4.2A What else is important?**
+
+- a) short duration of treatment
+- b) an electronic bill
+- c) regular appointments**
+- d) a short avenue
+
+#### **5.1A What else does he request?**
+
+- a) a bid
+- b) an opinion on gymnastic exercises**
+- c) sports medical examination
+- d) admission to a hospital
+- e) attestation to be incapable of work
+
+#### **5.2A What does he wants to be informed about?**
+
+- a) additional exercises**
+- b) additional acupuncture
+- c) taking a cure
+- d) new surgery method
+- e) new laser treatment
+
+#### **5.3V Which movement does he make?**
+
+- a) arm turn
+- b) neck turn
+- c) pelvis turn
+- d) back turn**
+
+#### **6.1A Gymnastic exercises are ... ?**
+
+- a) under tutelage of a physiotherapist**
+- b) conducted in a group
+- c) explained by the doctor
+- d) for free
+- e) in the neighbourhood
+
+#### **6.2A What does he expects from the exercises?**
+
+- a) get to know like-minded patients
+- b) allaying of pain
+- c) good complement to the treatment**
+- d) rapid improved performance
+- e) an amusing evening
+
+#### **6.3V Which movement does he make?**
+
+- a) arm turn
+- b) squat
+- c) pelvis turn
+- d) back turn**
+
+#### **7.1A The patent is concerned about ...?**
+
+- a) potential close-down of the doctor's practice
+- b) the treatment being fully paid by insurance**
+- c) savings for the family insurances
+- d) the meaningfulness of his treatment
+
+- e) increase of medication prices
+
+#### **8.1A Which costs is the insurance supposed to borne?**
+
+- a) **complete costs**
+- b) just necessary medicine
+- c) lease costs for the practice
+- d) parking fee during treatment
+- e) travel expenses
+
+#### **8.2A Who is to bear the expenses?**
+
+- a) occupation cooperative
+- b) **health insurance**
+- c) insurance for accident costs
+- d) employer
+- e) his wife
+
+#### **8.3v What does he show to the camera?**
+
+- a) **newspaper**
+- b) magazine
+- c) catalogue
+- d) straps
+- e) crutches
+
+#### **9.1A What does he want to arrange?**
+
+- a) appointment with a psychotherapist
+- b) discussion about cost sharing
+- c) **appointment with a dentist**
+- d) attendance at a scientific conference
+- e) appointment for a heating repair
+
+#### **9.2A Who is Dr Kollwitz?**
+
+- a) **partner in the group practice**
+- b) wife of the doctor
+- c) wife of the patient
+- d) another patient
+- e) sister of the patient
+
+#### **10.1A Why does he want an appointment later?**
+
+- a) fear of visiting a dentist
+- b) missing the appropriate funds currently
+- c) **he is very busy currently**
+- d) dentist does not have appointments on short notice
+- e) he has to contact his insurance company first
+
+#### **10.2A Why does he want to visit the dentist apparently?**
+
+- a) root canal therapy
+- b) routine checkup**
+- c) refund of costs
+- d) complaint about wrong diagnosis
+- e) complaint about poor quality
+
+#### **10.3V Which days are marked in the calendar?**
+
+- a) Monday to Wednesday**
+- b) Tuesday to Thursday
+- c) Wednesday to Friday
+
+(German)
+
+#### **1.1A Weshalb ruft der Patient an?**
+
+- a) er möchte einen Mitarbeiter sprechen
+- b) er hat sich verwählt
+- c) er möchte einen Termin zur Behandlung**
+- d) er braucht ein Rezept
+- e) er braucht eine Impfung
+
+#### **1.2AV Welche Beschwerden hat die Patientin?**
+
+- a) Zahnschmerzen
+- b) Rückenbeschwerden**
+- c) einen verstauchten Fuß
+- d) er beschwert sich über die Behandlung
+- e) bohrenden Kopfschmerz
+
+#### **1.3V Welches Körperteil zeigt die Patientin?**
+
+- a) Rücken**
+- b) Schulter
+- c) Handgelenk
+- d) Ellbogen
+- e) Nacken
+
+#### **2.1A Möchte die Patientin die Therapie ...**
+
+- a) ... beginnen?**
+- b) ... bezahlen?
+- c) ... beenden?
+- d) ... unterbrechen?
+- e) ... ändern?
+
+#### **2.2A Wie lange soll die Behandlung dauern?**
+
+- a) 1 Woche
+- b) 1 Jahr
+- c) 6 Wochen**
+
+- d) 2 Wochen
+- e) 5 Tage
+
+#### **2.3A Was für eine Behandlung soll sie bekommen?**
+
+- a) Tabletten
+- b) Bestrahlungen**
+- c) Infusionen
+
+#### **2.4V Welches Datum ist in dem Kalender zu sehen?**
+
+- a) Montag, der 15.
+- b) Dienstag, der 16.
+- c) Mittwoch, der 17.
+- d) Donnerstag, der 18.
+- e) Freitag, der 19.
+
+#### **3.1AV Welche Tage bevorzugt die Patientin?**
+
+- a) nur mittwochs
+- b) werktags
+- c) dienstags und donnerstags**
+- d) den 13. und 14. Februar
+- e) am Wochenende
+
+#### **3.2A Wann kann die Patientin nicht?**
+
+- a) am Wochenende
+- b) vormittags**
+- c) in der nächsten Woche
+- d) bei schlechter Witterung
+- e) am Abend
+
+#### **3.3V Welche Tage sind im Kalender markiert?**
+
+- a) Montag und Dienstag
+- b) Dienstag und Donnerstag
+- c) Donnerstag und Samstag
+- d) Mittwoch**
+
+#### **4.1A Warum kann der Anrufer mittwochs nicht?**
+
+- a) Termin beim Zahnarzt
+- b) Fußballtraining
+- c) Sprachkurs**
+- d) Betreuung der Großmutter
+- e) Arbeit als Zeitungsausträger
+
+#### **4.2A Was ist ihm noch wichtig?**
+
+- a) eine kurze Behandlungsdauer
+- b) eine elektronische Rechnung
+- c) regelmäßige Termine**
+
+- d) eine kurze Anreise
+
+#### **5.1A Was möchte die Patientin außerdem vom Arzt?**
+
+- a) einen Kostenvoranschlag
+- b) **seine Meinung zu zusätzlicher Gymnastik**
+- c) ein sportmedizinisches Gutachten
+- d) eine Einweisung ins Krankenhaus
+- e) eine Arbeitsunfähigkeitsbescheinigung
+
+#### **5.2A Über welchen Nutzen will sich der Anrufer informieren?**
+
+- a) **von zusätzlicher Gymnastik**
+- b) von zusätzlicher Akupunktur
+- c) eines Kuraufenthalts
+- d) einer neuen Operationsmethode
+- e) einer Laserbehandlung
+
+#### **5.3V Welche Bewegung macht die Patientin?**
+
+- a) Armdrehung
+- b) Nackendrehung
+- c) Beckendrehung
+- d) **Rückendrehung**
+
+#### **6.1A Wie sollen die Gymnastikkurse sein?**
+
+- a) **mit Anleitung durch eine Krankengymnastin**
+- b) Übung in einer größeren Gruppe
+- c) Einweisung vom Arzt selbst
+- d) kostenfrei
+- e) nahe seines Wohnortes
+
+#### **6.2A Was erhofft sich die Patientin von den Kursen?**
+
+- a) gleichgesinnte Patienten kennenzulernen
+- b) Schmerzminderung
+- c) **gute Ergänzung der Behandlung**
+- d) kurzfristige Leistungssteigerung
+- e) einen unterhaltsamen Abend
+
+#### **6.3V Welche Bewegung macht die Patientin?**
+
+- a) Armdrehung
+- b) Kniebeuge
+- c) Beckendrehung
+- d) **Rückendrehung**
+
+#### **7.1A Worüber ist die Patientin verunsichert?**
+
+- a) mögliche Schließung der Arztpraxis
+- b) **mögliche Erhöhung der Eigenbeteiligung**
+- c) Einsparungen bei der Familienversicherung
+
+- d) ob seine Behandlung überhaupt sinnvoll ist
+- e) Erhöhung der Arzneimittelpreise
+
+#### **8.1A Welche Kosten soll die Krankenkasse übernehmen?**
+
+- a) **kompletten Behandlungskosten**
+- b) nur notwendige Medikamente
+- c) Mietkosten der Arztpraxis
+- d) Parkgebühren während der Behandlungszeiten
+- e) Fahrtkosten zur Behandlung
+
+#### **8.2A Wer soll die Kosten der Behandlung übernehmen?**
+
+- a) die Berufsgenossenschaft
+- b) **die Krankenkasse**
+- c) die Unfallkasse
+- d) der Arbeitgeber
+- e) seine Frau
+
+#### **8.3v Was zeigt die Patient vor der Kamera?**
+
+- a) **Zeitung**
+- b) Magazine
+- c) Broschüre
+- d) Bänder
+- e) Krücken
+
+#### **9.1A Was möchte die Patientin vereinbaren?**
+
+- a) Termin mit dem Psychotherapeuten
+- b) Gespräch wegen der Kostenbeteiligung
+- c) **Termin mit der Zahnärztin**
+- d) Teilnahme an einem wissenschaftlichen Kongress
+- e) Termin zur Heizungsreparatur
+
+#### **9.2A Wer ist Frau Dr. Kollwitz?**
+
+- a) **Praxispartnerin des Arztes**
+- b) Ehefrau des Arztes
+- c) Ehefrau des Patienten
+- d) Patientin
+- e) Schwester des Patienten
+
+#### **10.1A Warum wünscht die Patientin einen späteren Termin?**
+
+- a) Angst vor dem Zahnarztbesuch
+- b) im Moment fehlen die finanziellen Mittel
+- c) **sie ist sehr beschäftigt**
+- d) Zahnärztin vergibt keine kurzfristigen Termine
+- e) sie muss erst bei der Krankenkasse anfragen
+
+#### **10.2A Warum will sie anscheinend zum Zahnarzt?**
+
+- a) Wurzelbehandlung
+- b) Routineuntersuchung**
+- c) Kostenrückerstattung
+- d) Beschwerde über eine falsche Diagnose
+- e) Beschwerde über mangelhafte Leistungen
+
+#### **10.3V Welche Tage sind in dem Kalender markiert?**
+
+- a) Montag bis Mittwoch**
+- b) Dienstag bis Donnerstag
+- c) Mittwoch bis Freitag
+
+### **Scenario 2: Car Rental**
+
+#### **1.1A What does the customer need?**
+
+- a) a car**
+- b) information
+- c) a lift
+- d) tickets for the opera
+- e) an electrician
+
+#### **1.2A The customer wants to ...**
+
+- a) sell a car
+- b) buy a car
+- c) rent a car**
+- d) repair a car
+- e) return a car
+
+#### **1.3V What is the name of the magazine?**
+
+- a) Autonet**
+- b) Automobile Mag
+- c) Cars
+- d) Automobile News
+- e) Cars Week
+
+#### **2.1AV What does the customer need?**
+
+- a) sweets
+- b) a bigger estate car**
+- c) a camper
+- d) a motorcycle
+- e) a cabriolet
+
+#### **2.2AV What alternative type of car would be OK?**
+
+- a) small bus
+- b) small van**
+- c) compact car
+
+- d) large limousine
+- e) pickup
+
+#### **2.3V What colour was the car?**
+
+- a) grey
+- b) **black**
+- c) green
+- d) red
+- e) white
+
+#### **3.1AV On which day does she need it?**
+
+- a) yesterday
+- b) next Sunday
+- c) **Wednesday**
+- d) today
+- e) Saturday
+
+#### **3.2AV When does she want to rent it?**
+
+- a) in the morning
+- b) **8.30 p.m.**
+- c) in the morning or in the evening
+- d) at noon
+- e) in the morning or at midday
+
+#### **4.1AV On what other day could she take the car?**
+
+- a) **Weekend**
+- b) Wednesday
+- c) Tuesday
+- d) Thursday
+- e) Friday
+
+#### **4.2A In what case could she even agree with the weekend?**
+
+- a) traffic jam
+- b) **special rate**
+- c) bad weather
+- d) complementary insurance
+- e) never
+
+#### **4.3AV Which days are marked in the calendar? (depends on the calendar)**
+
+- a) Monday and Tuesday
+- b) Monday and Wednesday
+- c) Tuesday and Thursday
+- d) Tuesday and Friday
+- e) None
+
+#### **5.1A What is important to the caller?**
+
+- a) price
+- b) **insurance**
+- c) driving comfort
+- d) colour
+- e) year of construction
+
+#### **5.2A What else does she want to rent?**
+
+- a) elevating truck
+- b) carrying strap
+- c) **trolley**
+- d) tail pulley
+- e) belt
+
+#### **6.1A What kind of packaging material does she want?**
+
+- a) packaging foil
+- b) boxes
+- c) **blankets**
+- d) paper
+- e) foam material
+
+#### **6.2A How much mileage allowance does she want?**
+
+- a) 10 km
+- b) 100 km
+- c) **500 km**
+- d) 5000 km
+- e) 50 km
+
+#### **7.1AV What does the customer show?**
+
+- a) customer number
+- b) **credit card**
+- c) membership number for automobile association
+- d) telephone number
+- e) address
+
+#### **7.2AV What paying facility does she choose?**
+
+- a) cash on delivery
+- b) **credit card**
+- c) advanced payment
+
+#### **7.3V Which card was used?**
+
+- a) Maestro
+- b) **Visa**
+- c) Master Card
+- d) Cirrus
+
+e) American Express
+
+#### **8.1A What car did she rent last time?**
+
+- a) BMW
+- b) **GOLF**
+- c) FORD
+- d) POLO
+- e) PORSCHE
+
+#### **8.2AV When did she rent a car last time?**
+
+- a) never
+- b) last summer
+- c) **beginning of the month**
+- d) last week
+- e) 1999
+
+#### **8.3V Which day is marked in the calendar? (depends of the calendar)**
+
+- a) Monday
+- b) Tuesday
+- c) Wednesday
+- d) Thursday
+- e) Friday
+
+#### **9.1AV When does she want to be billed?**
+
+- a) not at all, because of debit payment
+- b) Friday
+- c) **the next morning**
+- d) directly when returning the car
+- e) in the next afternoon
+
+#### **9.2A In which condition was the car returned last time?**
+
+- a) washed
+- b) **fully fuelled**
+- c) without the boxes
+- d) damaged
+- e) too late
+
+#### **9.3V Which day is marked? (depends of the calendar)**
+
+- a) Monday
+- b) Tuesday
+- c) Wednesday
+- d) Thursday
+- e) Friday
+
+#### **10.1A When will she return the car?**
+
+- a) **at the evening**
+- b) in the morning
+- c) never
+- d) midday
+- e) the next day
+
+#### **10.2A Where does she return the car to?**
+
+- a) petrol station
+- b) home
+- c) **car park**
+- d) basement garage
+- e) companies entrance
+
+#### **10.3V What does she show?**
+
+- a) **a card**
+- b) a bill
+- c) car keys
+- d) a calendar
+- e) a credit card
+
+(German)
+
+#### **1.1A Was möchte der Kunde?**
+
+- a) **einen Wagen**
+- b) eine Auskunft
+- c) eine Mitfahrgelegenheit
+- d) Opernkarten
+- e) einen Elektriker
+
+#### **1.2A Der Kunde will einen Wagen ...**
+
+- a) ... verkaufen
+- b) ... kaufen
+- c) **... reservieren**
+- d) ... reparieren lassen
+- e) ... zurückgeben
+
+#### **1.3V Wie heißt die Zeitschrift Magazin?**
+
+- a) **... Autonet**
+- b) ... Automobil mag
+- c) ... Autobild
+- d) ... Autoexpress
+- e) ... Autoweek
+
+#### **2.1AV Was braucht der Kunde?**
+
+- a) Gummibärchen
+- b) größeren Kombi**
+- c) Campingwagen
+- d) Motorrad
+- e) Cabrio
+
+#### **2.2AV Welche Fahrzeuggröße benötigt er mindestens?**
+
+- a) kleinerer Bus
+- b) größerer Kombi**
+- c) Kompaktwagen
+- d) größere Limousine
+- e) Pritschenwagen
+
+#### **2.3V Was ist die Autofarbe?**
+
+- a) grau
+- b) schwarz**
+- c) grün
+- d) rot
+- e) weiß
+
+#### **3.1AV An welchem Tag möchte er vorbeikommen?**
+
+- a) am vorhergehenden Tag
+- b) nächsten Sonntag
+- c) kommenden Mittwoch / Mittwoch**
+- d) heute
+- e) Samstag
+
+#### **3.2AV Wann würde er den Wagen abholen?**
+
+- a) früh morgens
+- b) 20:00h**
+- c) morgens oder abends
+- d) 12 h
+- e) morgens oder mittags
+
+#### **4.1AV An welchen alternativen Termin könnte der Wagen auch abgeholt werden?**
+
+- a) Wochenende**
+- b) Mittwoch
+- c) Dienstag
+- d) Donnerstag
+- e) Freitag
+
+**4.2A In welchem Fällen könnte er den Wagen sogar am Wochenende abholen?**
+
+- a) bei Stau
+- b) bei einem Spezialtarif**
+- c) bei schlechtem Wetter
+- d) bei einer Zusatzversicherung
+- e) nie
+
+**4.3AV Welche Tage sind am Kalender markiert?**
+
+- a) Montag und Dienstag
+- b) Montag und Mittwoch
+- c) Dienstag und Donnerstag
+- d) Dienstag und Freitag
+- e) Keiner
+
+**5.1A Was ist wichtig für den Kunden?**
+
+- a) Preis
+- b) Versicherung**
+- c) Fahrkomfort
+- d) Farbe
+- e) Baujahr
+
+**5.2A Was soll zusätzlich gemietet werden?**
+
+- a) Hubwagen
+- b) Tragegurt
+- c) Rollwagen**
+- d) Flaschenzug
+- e) Befestigungsgurte
+
+**6.1A Was für Verpackungsmaterial benötigt der Kunde?**
+
+- a) Verpackungsfolie
+- b) Kartons
+- c) Decken**
+- d) Papier
+- e) Schaumstoff
+
+**6.2A Wie hoch soll die Kilometerpauschale mindestens sein?**
+
+- a) 10 km
+- b) 100 km
+- c) 500 km**
+- d) 5000 km
+- e) 50 km
+
+#### **7.1AV Was zeigt der Kunde vor?**
+
+- a) Kundennummer
+- b) Kreditkarte**
+- c) ADAC Mitgliedsnummer
+- d) Telefonnummer
+- e) Adresse
+
+#### **7.2AV Wie möchte der Kunde bezahlen?**
+
+- a) Nachnahme
+- b) Kreditkarte**
+- c) Vorkasse
+
+#### **7.3V Welche Karte würde verwendet?**
+
+- a) Maestro
+- b) Visa**
+- c) Mastercard
+- d) Cirrus
+- e) American Express
+
+#### **8.1A Was hat der Kunden schon gemietet?**
+
+- a) BMW
+- b) GOLF**
+- c) FORD
+- d) POLO
+- e) PORSCHE
+
+#### **8.2AV Wann hatte er das letzte mal einen Wagen gemietet?**
+
+- a) noch nie
+- b) letzten Sommer
+- c) Anfang des Monats**
+- d) letzte Woche
+- e) 1999
+
+#### **8.3V Welcher Tag ist am Kalender angemerkt?**
+
+- a) Montag
+- b) Dienstag
+- c) Mittwoch
+- d) Donnerstag
+- e) Freitag
+
+#### **9.1AV Wann kommt er zur Abrechnung?**
+
+- a) gar nicht, wegen Lastschrifteinzug
+- b) am Freitag
+- c) am darauffolgenden Morgen**
+- d) gleich bei der Abgabe des Fahrzeuges
+
+e) am darauffolgenden Nachmittag
+
+#### **9.2A Wie hat er den Wagen beim letzten Mal zurückgegeben?**
+
+- a) gewaschen
+- b) **vollgetankt**
+- c) ohne Umzugskisten
+- d) beschädigt
+- e) zu spät
+
+#### **9.3V Welcher Tag ist am Kalender markiert?**
+
+- a) Montag
+- b) Dienstag
+- c) Mittwoch
+- d) Donnerstag
+- e) Freitag
+
+#### **10.1A Wann kommt den Kunden zurück?**
+
+- a) **am Abend**
+- b) am Morgen
+- c) nie
+- d) am Mittag
+- e) noch einen Tag später
+
+#### **10.2A Wohin fährt er den Wagen bei der Rückgabe?**
+
+- a) Tankstelle
+- b) nach Hause
+- c) **Firmenparkplatz**
+- d) Tiefgarage
+- e) Firmeneinfahrt
+
+#### **10.3V Was zeigt der Kunde vor der Kamera?**
+
+- a) **Eine Karte**
+- b) Eine Rechnung
+- c) Die Autoschlüssel
+- d) Ein Kalender
+- e) Eine Kreditkarte
+
+### **Scenario 3: Kitchen purchase order**
+
+#### **1.1A Why does the customer call?**
+
+- a) He misdialled
+- b) wants to rent a car
+- c) **wants to order a kitchen**
+- d) wants to order a taxi
+- e) order opera tickets
+
+#### **1.2A What does he ask for?**
+
+- a) to speak Mrs Müller**
+- b) to speak the boss
+- c) to get a discount
+- d) to obtain a telephone number
+- e) to speaker Mr Braun
+
+#### **1.3V What does the customer show?**
+
+- a) his business card
+- b) a novel
+- c) a catalogue with a kitchen**
+- d) a microphone
+- e) a mobile phone
+
+#### **2.1A What is Mrs Müller's business?**
+
+- a) sales advisory service of consumer electronics
+- b) sales advisory service in the salesroom**
+- c) sales of car insurances
+- d) warehousing
+- e) training
+
+#### **2.2A What did both agree upon?**
+
+- a) Mrs Müller will contact him
+- b) He will wait for a call
+- d) He will contact her not before Thursday
+- d) He will call her until Wednesday**
+- e) He will pass by
+
+#### **3.1AV On which colour did he decide?**
+
+- a) white
+- b) red
+- c) light grey**
+- d) green
+- e) blue
+
+#### **3.2A Why did he not choose white?**
+
+- a) stains are easily visible
+- b) it does not fit with the cooker
+- c) out of stock
+- d) difficult to maintain
+- e) appears too cold**
+
+#### **3.3A How fast did he decide against white?**
+
+- a) after giving a thought**
+- b) immediately
+
+- c) very fast
+
+#### **4.1AV Which door knobs does he like best?**
+
+- a) round shape
+- b) none
+- c) shape of pyramid
+- d) conus shape
+- e) **lozenge shape**
+
+#### **4.2A What does he not like with the round shape?**
+
+- a) too ugly
+- b) edges too sharp
+- c) **too small**
+- d) too big
+- e) the colour
+
+#### **4.3AV Which colour were the door knobs?**
+
+- a) **grey**
+- b) black
+- c) gold
+- d) wood like
+- e) white
+
+#### **5.1AV What is chosen to be small in favour of the dishwasher?**
+
+- a) the wall cupboard
+- b) the fridge
+- c) the rubbish bin
+- d) **the sink**
+- e) the cooker
+
+#### **5.2A Why did he decide on a single sink?**
+
+- a) **to save space**
+- b) to save money
+- c) because he only needs one
+- d) to save time
+- e) he was told to
+
+#### **5.3V How many sinks are shown?**
+
+- a) one
+- b) zero
+- c) **two**
+
+#### **6.1A What does he ask about the dishwasher?**
+
+- a) if it is on offer
+- b) **if it provides aqua-stop**
+- c) if it is also available in grey
+
+#### **6.2A What does the washer have to provide?**
+
+- a) sound absorber
+- b) special washing programs
+- c) transportable weights
+- d) high usability
+- e) **aqua-stop**
+
+#### **6.3A If the model does not meet the requirements ...**
+
+- b) **he orders the next bigger model**
+- a) he rather takes none at all
+- c) he wants to complain about it
+- d) he will return it
+- e) he wants a special offer
+
+#### **7.1A Which cooker did he choose?**
+
+- a) the largest
+- b) AEG
+- c) **none so far**
+- d) MIELE
+- e) BAUKNECHT
+
+#### **7.2AV What kind of top does he wants for his cooker?**
+
+- a) **glass-ceramic**
+- b) a gas-stove
+- c) steel
+- d) cast iron
+- e) enamel
+
+#### **7.3V How much does the cooker cost? (depends on the catalogue)**
+
+- a) 2999
+- b) 299
+- c) 499
+- d) **1999**
+- e) 699
+
+#### **8.A What else should the cooker provide?**
+
+- a) ceramic top
+- b) fridge
+- c) sink
+- d) freezer
+- e) **sensor-circuitry**
+
+#### **9.A How big is the table supposed to be?**
+
+- a) 100 x 100
+- b) **100 x 160**
+
+- d) 60 x 60
+
+#### **10.1A How much should the table be extendable?**
+
+- a) only in its height
+- b) 200 cm
+- c) **150 cm**
+- d) 80 cm
+
+(German)
+
+#### **1.1A Aus welchem Grund ruft der Kunde an?**
+
+- a) verwählt
+- b) er möchte ein Auto bestellen
+- c) **er möchte eine Küche bestellen**
+- d) bestellen eines Taxis
+- e) bestellen von Kinokarten
+
+#### **1.2A Wonach fragt der Kunde?**
+
+- a) **nach Frau Müller**
+- b) nach dem Chef
+- c) nach einem Rabatt
+- d) nach einer Telefonnummer
+- e) nach Herrn Braun
+
+#### **1.3V Was zeigt der Kunde?**
+
+- a) eine Visitenkarte
+- b) einen Roman
+- c) **eine Broschüre einer Küche**
+- d) ein Mikrofon
+- e) ein Handy
+
+#### **2.1A Was macht Frau Müller?**
+
+- a) Beratung für Unterhaltungselektronik
+- b) **Beratung in den Verkaufsräumen**
+- c) Beratung für Autoversicherungen
+- d) Lagerhaltung
+- e) Fortbildungen
+
+#### **2.2A Was hatte der Kunde vereinbart?**
+
+- a) Frau Müller meldet sich bei ihm
+- b) er wartet auf einen Anruf
+- d) er meldet sich ab Donnerstag
+- d) **er meldet sich bis Mittwoch**
+- e) er kommt vorbei
+
+#### **3.1AV Für welche Farbe hat sich der Kunde entschieden?**
+
+- a) weiß
+- b) rot
+- c) **hellgrau**
+- d) grün
+- e) blau
+
+#### **3.2A Warum wurde nicht "weiß" gewählt?**
+
+- a) man sieht Flecken so schnell
+- b) passt nicht zum Herd
+- c) nicht vorrätig
+- d) schlecht zu pflegen
+- e) **wirkt zu kalt**
+
+#### **3.3A Wie schnell hat sie sich gegen "weiß" entschieden?**
+
+- a) **nach längerer Überlegung**
+- b) sofort
+- c) sehr schnell
+
+#### **4.1AV Welche Türknäufe mag er am liebsten?**
+
+- a) runde Form
+- b) gar keine
+- c) Pyramidenform
+- d) Kegelform
+- e) **Rautenform**
+
+#### **4.2A Was missfällt ihm an den runden Türknäufen?**
+
+- a) zu hässlich
+- b) zu scharfkantig
+- c) **zu klein**
+- d) zu groß
+- e) die Farbe
+
+#### **4.3AV Welche Farbe haben die Türknäufe?**
+
+- a) **grau**
+- b) schwarz
+- c) gold
+- d) holzfarben
+- e) weiß
+
+#### **5.1AV Was soll für die Spülmaschine kleiner werden?**
+
+- a) der Hängeschrank
+- b) der Kühlschränk
+- c) der Müllcontainer
+- d) **das Spülbecken**
+
+- e) der Herd
+
+#### **5.2A Warum will der Kunde nur ein Becken bestellen?**
+
+- a) **um Platz zu sparen**
+- b) um Geld zu sparen
+- c) weil er nichts anderes braucht
+- d) um Zeit zu sparen
+- e) weil es ihm empfohlen wurde
+
+#### **5.3V Wie viel Becken werden gezeigt?**
+
+- a) 1
+- b) 0
+- c) **2**
+
+#### **6.1A Was fragt der Kunde zu der Spülmaschine?**
+
+- a) ob sie angeboten wird
+- b) ob Aqua-stop verfügbar ist
+- c) ob es sie in hellgrau gibt
+
+#### **6.2A Über was soll die Maschine verfügen?**
+
+- a) Geräuschdämpfer
+- b) spezielle Waschprogramme
+- c) herausnehmbare Gewichte
+- d) einfache Bedienung
+- e) **Aqua-Stop**
+
+#### **6.3A Wenn die Maschine nicht ihren Wünschen entspricht ...**
+
+- b) **... nimmt er die nächst größere**
+- a) ... nimmt sie lieber keine
+- c) ... will sie sich beschweren
+- d) ... gibt es sie zurück
+- e) ... will sie einen Rabatt
+
+#### **7.1A Welchen Herd hat er sich ausgesucht?**
+
+- a) den Größten
+- b) AEG
+- c) **noch keinen**
+- d) MIELE
+- e) BAUKNECHT
+
+#### **7.2AV Was für ein Kochfeld soll der Herd haben?**
+
+- a) **Glaskeramik**
+- b) Gas
+- c) Edelstahl
+- d) Gusseisen
+- e) Emaille
+
+#### **7.3V Wie viel kostet das Kochfeld?**
+
+- a) 2999
+- b) 299
+- c) 499
+- d) 1999**
+- e) 699
+
+#### **8.A Was soll integriert sein?**
+
+- a) Kochfeld
+- b) Kühlschrank
+- c) Becken
+- d) Tiefkühlschrank
+- e) Sensorsteuerung**
+
+#### **9.A Wie groß soll die Mikrowelle sein?**
+
+- a) 100 x 100**
+- b) 100 x 160
+- d) 60 x 60
+
+#### **10.1A Auf welche Länge will er den Tisch vergrößern?**
+
+- a) er soll nur in der Höhe verstellbar sein
+- b) 100 cm
+- c) 150 cm**
+- d) 80 cm
+
+### **Scenario 4: Bithday party**
+
+#### **1.1A Who is celebrating his birthday?**
+
+- a) Peter**
+- b) Jan
+- c) Jens
+- d) Niklas
+
+#### **1.2A The birthday party was ...**
+
+- b) last Monday
+- c) last Thursday
+- a) last Saturday**
+- d) last Wednesday
+
+#### **1.3V What is the caller doing with her hands?**
+
+- a) waving**
+- b) folding
+- c) grabbing
+
+#### **2.1A Who does she met there?**
+
+- b) Peter's friends
+- a) old friends**
+
+- c) her professor
+- d) Jan's girl-friend
+
+#### **2.2A What are the names of the people from the photo?**
+
+- b) Stefan, Linda and Peter
+- c) Stefan, Jens and Markus
+- a) Stefan, Linda and Markus**
+
+#### **2.3AV What does she present to the camera?**
+
+- b) a photo of Peter
+- c) a photo of her parents
+- a) a photo of an old friend**
+- d) a photo of her at the party
+
+#### **3.1AV What happened after the meal?**
+
+- a) a small concert**
+- b) a theatre play
+- c) a dance show
+
+#### **3.2A How was the atmosphere?**
+
+- b) tensed situation
+- a) spirits were running high**
+- c) everyone felt giddy
+- d) sad
+
+#### **4.1A Whom did she meet there?**
+
+- a) Julia from school**
+- b) her brother
+- c) her kindergarten teacher
+- d) Peter's father
+
+#### **4.2V What is Julia doing according to the photo?**
+
+- b) she is reading
+- c) she is eating
+- d) she sleeps
+- a) she is dancing**
+
+#### **4.3V What kind of movement is she doing?**
+
+- a) a break-dance move**
+- b) a gymnastics exercise
+- c) she turns over
+
+#### **5.1A Who baked the cake?**
+
+- a) Jens
+- b) Peter
+- c) Peter's mother**
+- d) Julia
+
+**5.2A The guest gathered at midnight in order to ...**
+
+- b) go out dancing
+- c) hand over the presents
+- d) bake a cake
+- a) sing happy birthday**
+
+**5.3V Which colour was the cake?**
+
+- a) white and red**
+- b) green
+- c) brown
+- d) white
+
+**6.1AV What was Peter's birthday present?**
+
+- b) a guitar
+- c) a piano
+- d) a violin
+- a) a drum set**
+
+**6.2A When did Peter receive his present?**
+
+- a) before eating the cake**
+- b) after eating the cake
+- c) at dawn
+- d) the next day
+
+**7.1A What did Peter and his friends laughed about?**
+
+- b) Peter's jokes
+- c) the party
+- a) the past**
+- d) at Peter's brother
+
+**8.1A Which song did she sing?**
+
+- b) a drinking song
+- a) a children's song**
+- c) a national anthem
+- d) a birthday song
+
+**8.2A Why did she sing?**
+
+- b) for Peter's birthday
+- c) without any reason
+- d) to accompany the band
+- a) Peter's brother had to go to sleep**
+
+**9.1A What did she learn?**
+
+- a) eating with chopsticks**
+- b) a dance move
+- c) a fight move
+
+- d) baking a cake
+
+#### **9.2AV What was she playing with?**
+
+- b) a pen
+- a) Chinese chopsticks**
+- c) a spoon
+- d) her mobile phone
+
+#### **9.3A Who taught her to use chopsticks?**
+
+- a) Peter's parents**
+- b) Peter
+- c) Peter's brother
+- d) Lina
+
+#### **10.1A About Jan, she want to ...**
+
+- b) play soccer together
+- c) have dinner
+- a) meet each other**
+- d) discuss issues
+
+#### **10.2V What is she doing at the end?**
+
+- a) waving**
+- b) juggling
+- c) clapping
+
+(German)
+
+#### **1.1A Wer feiert seinen Geburtstag?**
+
+- a) Peter**
+- b) Jan
+- c) Jens
+- d) Niklas
+
+#### **1.B Die Geburtstagfeier war...**
+
+- b) letzten Montag
+- c) letzten Donnerstag
+- a) letzten Samstag**
+- d) letzten Mittwoch
+
+#### **1.3B Was macht sie mit ihren Händen vor der Kamera?**
+
+- a) winken**
+- b) falten
+- c) greifen
+
+#### **2.1A Wen hat sie bei der Party getroffen?**
+
+- b) Peters Freunde
+- a) alte Bekannte**
+- c) ihren Professor
+
+d) Jans Freundin
+
+#### **2.2A Wie heißen die Leute, die auf dem Foto sind?**
+
+b) Stefan, Linda und Peter
+
+c) Stefan, Jens und Markus
+
+**a) Stefan, Linda und Markus**
+
+#### **2.3AV Was zeigt sie vor der Kamera?**
+
+b) ein Foto von Peter
+
+c) ein Foto von seinen Eltern
+
+**a) ein Foto von alten Freunden**
+
+d) ein Foto von ihr bei der Party
+
+#### **3.1AV Welche Veranstaltung findet nach dem Essen statt?**
+
+**a) ein kleines Konzert**
+
+b) ein Theaterstück
+
+c) eine Tanzshow
+
+#### **3.2A Wie war die Stimmung?**
+
+b) gespannt
+
+**a) ausgelassen**
+
+c) euphorisch
+
+d) traurig
+
+#### **4.1A Wen hat sie bei der Party plötzlich getroffen?**
+
+**a) ihre alte Schulfreundin Julia**
+
+b) ihren Bruder
+
+c) ihren Kindergartenlehrer
+
+d) Peters Vater
+
+#### **4.2V Was macht Julia auf dem Foto?**
+
+b) sie liest
+
+c) sie isst
+
+d) sie schläft
+
+**a) sie tanzt**
+
+#### **4.3V Was macht sie für eine Bewegung?**
+
+**a) ein Breakdance-Bewegung**
+
+b) eine Gymnastik-Bewegung
+
+c) sie dreht sich um
+
+#### **5.1A Wer hat den Kuchen gebacken?**
+
+a) Jens
+
+b) Peter
+
+**c) Peters Mutter**
+
+d) Julia
+
+**5.2A Die Gäste treffen sich gegen Mitternacht um ...**
+
+- b) ... tanzen zu gehen
+- c) ... Geschenke zu verschenken
+- d) ... einen Kuchen zu backen
+- a) ... Happy Birthday zu singen**
+
+**5.3V Welche Farbe hat der Kuchen?**
+
+- a) weiß und rot**
+- b) grün
+- c) braun
+- d) weiß
+
+**6.1AV Was bekommt Peter als Geburtstagsgeschenk?**
+
+- b) eine Gitarre
+- c) ein Klavier
+- d) eine Geige
+- a) ein Schlagzeug**
+
+**6.2A Wann hat Peter sein Geburtstagsgeschenk bekommen?**
+
+- a) vor dem Kuchen**
+- b) nach dem Kuchen
+- c) am Ende der Nacht
+- d) am folgenden Tag
+
+**7.1A Worüber haben sie und ihre Freunde gelacht?**
+
+- b) Peters Witze
+- c) die Party
+- a) die Vergangenheit**
+- d) Peters Bruder
+
+**8.1A Welches Lied hat sie gesungen?**
+
+- b) ein Trinklied
+- a) ein Kinderlied**
+- c) die Nationalhymne
+- d) ein Geburtstagslied
+
+**8.2A Warum hat sie gesungen?**
+
+- b) um Peter ein Geburtstagslied zu singen
+- c) ohne Grund
+- d) um bei der Band mitzusingen
+- a) Peters Bruder musste ins Bett gehen**
+
+**9.1A Was hat sie gelernt?**
+
+- a) essen mit Essstäbchen**
+- b) eine Tanzbewegung
+- c) eine Kampfbewegung
+
+- d) einen Kuchen zu backen
+
+#### **9.2AV Mit welchem Objekt spielt sie?**
+
+- b) Einem Stift
+- a) Chinesischen Essstäbchen**
+- c) einer Gabel
+- d) seinem Handy
+
+#### **9.3A Wer hat ihr beigebracht, mit Essstäbchen zu essen?**
+
+- a) Peters Eltern**
+- b) Peter
+- c) Peters Bruder
+- d) Lina
+
+#### **10.2A Mit Jan wünscht sie sich ...**
+
+- b) zusammen Fußball zu spielen
+- c) zusammen essen zu gehen
+- a) sich bald wiedersehen**
+- d) wichtige Dinge zu diskutieren
+
+#### **10.3V Was macht sie zum Abschluss?**
+
+- a) winken**
+- b) jonglieren
+- c) klatschen
+
+# Appendix III
+
+(This appendix does not form an integral part of this Recommendation.)
+
+The purpose of this appendix is to show examples on how to build test material profiles for time-varying transmission conditions. For building up prediction models, extreme profiles are interesting to find psychophysical effects. For applied goals, profiles can be adjusted to the apparent network conditions, which may be less extreme. The same profiles can be used on audio and video data, but stimuli can also be created applying separate profiles for both channels.
+
+![Figure III.1: Schematic illustration of the profiles used in [b-Belmudez et al., 2013]. The figure displays 15 profiles (profile 1 to profile 15) arranged in two columns. Each profile is a bar chart showing 'AV Quality' (or 'Video Quality' and 'Audio Quality') on the y-axis against five categories (1, 2, 3, 4, 5) on the x-axis. The profiles show varying levels of quality across the categories, with some profiles showing high quality across all categories (e.g., profile 1) and others showing more varied or lower quality (e.g., profile 15).](77a781dfb114c3e2b399f876f1808cfd_img.jpg)
+
+Figure III.1 displays 15 profiles (profile 1 to profile 15) arranged in two columns. Each profile is a bar chart showing 'AV Quality' (or 'Video Quality' and 'Audio Quality') on the y-axis against five categories (1, 2, 3, 4, 5) on the x-axis. The profiles show varying levels of quality across the categories, with some profiles showing high quality across all categories (e.g., profile 1) and others showing more varied or lower quality (e.g., profile 15).
+
+**Left Column Profiles:**
+
+- profile 1: AV Quality is high across all categories (1-5).
+- profile 2: AV Quality is high across all categories (1-5).
+- profile 3: AV Quality is low across all categories (1-5).
+- profile 4: AV Quality is low across all categories (1-5).
+- profile 5: AV Quality is high across all categories (1-5).
+- profile 6: AV Quality is high across all categories (1-5).
+- profile 7: AV Quality is high across all categories (1-5).
+- profile 8: AV Quality is high across all categories (1-5).
+- profile 9: AV Quality is high across all categories (1-5).
+- profile 10: AV Quality is high across all categories (1-5).
+- profile 11: AV Quality is high across all categories (1-5).
+
+**Right Column Profiles:**
+
+- profile 12: Video Quality is high across all categories (1-5); Audio Quality is low across all categories (1-5).
+- profile 13: Video Quality is high across all categories (1-5); Audio Quality is high across all categories (1-5).
+- profile 14: Video Quality is high across all categories (1-5); Audio Quality is low across all categories (1-5).
+- profile 15: Video Quality is low across all categories (1-5); Audio Quality is high across all categories (1-5).
+
+Figure III.1: Schematic illustration of the profiles used in [b-Belmudez et al., 2013]. The figure displays 15 profiles (profile 1 to profile 15) arranged in two columns. Each profile is a bar chart showing 'AV Quality' (or 'Video Quality' and 'Audio Quality') on the y-axis against five categories (1, 2, 3, 4, 5) on the x-axis. The profiles show varying levels of quality across the categories, with some profiles showing high quality across all categories (e.g., profile 1) and others showing more varied or lower quality (e.g., profile 15).
+
+Figure III.1 – Schematic illustration of the profiles used in [b-Belmudez et al., 2013]
+
+## Bibliography
+
+- [b-ETSI TR 102 506] ETSI TR 102 506 (2011), *Speech Processing, Transmission and Quality Aspects (STQ); "Estimating Speech Quality per Call"*, European Telecommunications Standards Institute, Sophia Antipolis.
+- [b-Belmudez et al., 2013] Belmudez, B., Lewcio, B., Möller, S. (2013), *Call Quality Prediction for Audiovisual Time-Varying Impairments Using Simulated Conversational Structures*, submitted to Acta Acustica united with Acustica 99(5), 792-805.
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| Series G        | Transmission systems and media, digital systems and networks                                |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K        | Protection against interference                                                             |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| <b>Series P</b> | <b>Terminals and subjective and objective assessment methods</b>                            |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

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+
+
+International Telecommunication Union
+
+# **ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **P.1305**
+
+(07/2016)
+
+SERIES P: TERMINALS AND SUBJECTIVE AND  
+OBJECTIVE ASSESSMENT METHODS
+
+Telemeeting assessment
+
+---
+
+## **Effect of delays on telemeeting quality**
+
+Recommendation ITU-T P.1305
+
+**ITU-T**
+
+![ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.](1d7527f4316cfe2d342b08d1653d1592_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking across it. To the right of the globe, the text "ITU" is written in a large, bold, blue font, and below it, "International Telecommunication Union" is written in a smaller, blue font.
+
+ITU logo: A globe with a red lightning bolt and the text 'ITU International Telecommunication Union'.
+
+# ITU-T P-SERIES RECOMMENDATIONS
+
+## TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS
+
+|                                                                                                    |               |               |
+|----------------------------------------------------------------------------------------------------|---------------|---------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality      | Series        | P.10          |
+| Voice terminal characteristics                                                                     | Series        | P.30          |
+|                                                                                                    |               | P.300         |
+| Reference systems                                                                                  | Series        | P.40          |
+| Objective measuring apparatus                                                                      | Series        | P.50          |
+|                                                                                                    |               | P.500         |
+| Objective electro-acoustical measurements                                                          | Series        | P.60          |
+| Measurements related to speech loudness                                                            | Series        | P.70          |
+| Methods for objective and subjective assessment of speech quality                                  | Series        | P.80          |
+| Methods for objective and subjective assessment of speech and video quality                        | Series        | P.800         |
+| Audiovisual quality in multimedia services                                                         | Series        | P.900         |
+| Transmission performance and QoS aspects of IP end-points                                          | Series        | P.1000        |
+| Communications involving vehicles                                                                  | Series        | P.1100        |
+| Models and tools for quality assessment of streamed media                                          | Series        | P.1200        |
+| <b>Telemeeting assessment</b>                                                                      | <b>Series</b> | <b>P.1300</b> |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                  | Series        | P.1400        |
+| Methods for objective and subjective assessment of quality of services other than speech and video | Series        | P.1500        |
+
+For further details, please refer to the list of ITU-T Recommendations.
+
+## Recommendation ITU-T P.1305
+
+# Effect of delays on telemeeting quality
+
+## Summary
+
+Recommendation ITU-T P.1305 has the primary purpose of describing the impact of echo-free transmission delays on telemeeting quality of experience (QoE). Delay has a major impact on the interaction performance of conference participants, but is not always explicitly noticed by them; its impact being commonly attributed to other participants behaviour rather than being a system feature.
+
+Before discussing the impact of the delays, it is useful to first consider how people behave when conversing in an ideal environment. Since this has been well studied in the linguistic discipline of conversation analysis (CA), a short discussion of conversations in that context and a discussion on the impact of delay from a CA perspective is included. Some analysis based on the alternative technique of conversation surface structures is also included.
+
+A secondary purpose of this Recommendation is to provide guidance on appropriate testing methods for evaluating the effect of delay in telemeetings.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T P.1305   | 2016-07-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/12974">11.1002/1000/12974</a> |
+
+## Keywords
+
+Conversation, conversation analysis, delay, subjective test, telemeeting.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2016
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|      |                                                                                                                | Page |
+|------|----------------------------------------------------------------------------------------------------------------|------|
+| 1    | Scope.....                                                                                                     | 1    |
+| 2    | References.....                                                                                                | 1    |
+| 3    | Definitions .....                                                                                              | 2    |
+| 3.1  | Terms defined elsewhere .....                                                                                  | 2    |
+| 3.2  | Terms defined in this Recommendation.....                                                                      | 3    |
+| 4    | Abbreviations and acronyms .....                                                                               | 3    |
+| 5    | Conventions .....                                                                                              | 3    |
+| 6    | Existing Recommendations concerning the subjective quality evaluation in case of pure transmission delay ..... | 3    |
+| 6.1  | Audio delay .....                                                                                              | 3    |
+| 6.2  | Video delay.....                                                                                               | 3    |
+| 6.3  | Synchronization between audio and video .....                                                                  | 4    |
+| 7    | Conversation features .....                                                                                    | 4    |
+| 7.1  | Two-party and multi-party conversations .....                                                                  | 4    |
+| 7.2  | Two analysis techniques.....                                                                                   | 4    |
+| 7.3  | Conversation analysis and turn-taking .....                                                                    | 5    |
+| 7.4  | Conversation structure and styles.....                                                                         | 7    |
+| 7.5  | Backchannels and other behaviours during conversations.....                                                    | 7    |
+| 7.6  | Conversation surface structure analysis .....                                                                  | 7    |
+| 8    | The impact of delay .....                                                                                      | 9    |
+| 8.1  | Turn-taking with delay .....                                                                                   | 9    |
+| 8.2  | Conversation surface structure and delays .....                                                                | 10   |
+| 8.3  | Multiparty and two-party conversations with delay.....                                                         | 11   |
+| 8.4  | Other side-impacts of delay.....                                                                               | 11   |
+| 9    | Factors influencing the impact of pure delay .....                                                             | 11   |
+| 9.1  | Audiovisual telemeetings .....                                                                                 | 11   |
+| 9.2  | User expectations.....                                                                                         | 12   |
+| 9.3  | Asymmetric delay between participants and co-location.....                                                     | 12   |
+| 9.4  | Interpersonal influences.....                                                                                  | 12   |
+| 10   | Testing methods.....                                                                                           | 12   |
+| 10.1 | General comments .....                                                                                         | 12   |
+| 10.2 | Conversational-opinion tests .....                                                                             | 13   |
+| 10.3 | Group interaction tests.....                                                                                   | 14   |
+| 10.4 | Communication system effectiveness tests .....                                                                 | 16   |
+| 10.5 | Micro-feature tests.....                                                                                       | 16   |
+| 11   | Areas for further research regarding the impact of delay .....                                                 | 17   |
+|      | Annex A – Suggestions for free-conversation tasks .....                                                        | 18   |
+
+|                                                      | Page |
+|------------------------------------------------------|------|
+| A.1 'Holiday' task .....                             | 18   |
+| A.2 Role-playing games .....                         | 18   |
+| A.3 "Who am I?" Celebrity Name-Guessing Task.....    | 18   |
+| A.4 Navigation tasks .....                           | 19   |
+| A.5 Story with missing parts .....                   | 19   |
+| A.6 Building blocks task – variation .....           | 19   |
+| A.7 Survival task – variations .....                 | 20   |
+| Annex B – Suggestions for delay-critical tasks ..... | 21   |
+| B.1 Information exchange tasks .....                 | 21   |
+| B.2 Random number verification task timed .....      | 21   |
+| Bibliography.....                                    | 22   |
+
+# Effect of delays on telemeeting quality
+
+# 1 Scope
+
+This Recommendation has the primary purpose of describing the impact of echo-free transmission delays on telemeeting quality of experience (QoE). Delay is special amongst communication impairments in that it can have a major impact on how well the users interact, but very often without them being explicitly aware of its presence. Typically users comment on its impact (e.g., "we kept on interrupting each other") or assume a delayed response is due to the other participants taking a long time to respond. Consequently its impact is not always captured in conversational-opinion tests. Crucially the impact has been shown to be highly dependent on the task or activity being undertaken.
+
+The focus in this Recommendation is therefore on the human factor – its purpose is not to define specific quantitative limits or values, discuss the sources of delay or to discuss methods of delay measurement or methods to reduce its impact.
+
+Before discussing the impact of the delays, it is useful to first consider how people behave when conversing in an ideal environment. Since this has been well studied in the linguistic discipline of conversation analysis (CA), a short discussion of conversations in that context and a discussion on the impact of delay from a CA perspective is included. Some analysis based on the alternative technique of conversation surface structures is also included.
+
+A secondary purpose of this Recommendation is to provide guidance on appropriate testing methods. A number of these have already been described in Annex D of [ITU-T P.1301] and will not be repeated here. However, there have been a number of new developments since that recommendation came into force and it is appropriate to expand on that knowledge.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T G.114] Recommendation ITU-T G.114 (2003), *One-way transmission time*.
+- [ITU-T G.131] Recommendation ITU-T G.131 (2003), *Talker echo and its control*.
+- [ITU-T P.800] Recommendation ITU-T P.800 (1996), *Methods for subjective determination of transmission quality*.
+- [ITU-T P.805] Recommendation ITU-T P.805 (2007), *Subjective evaluation of conversational quality*.
+- [ITU-T P.920] Recommendation ITU-T P.920 (2000), *Interactive test methods for audiovisual communications*.
+- [ITU-T P.1301] Recommendation ITU-T P.1301 (2012), *Subjective quality evaluation of audio and audiovisual multiparty telemeetings*.
+
+[ITU-T P.1312] Recommendation ITU-T P.1312 (2016), *Method for the measurement of the communication effectiveness of multiparty telemeetings using task performance*.
+
+[ITU-R BT.1359-1] Recommendation ITU-R BT.1359-1 (1998), *Relative timing of sound and vision for broadcasting*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 telemeeting** [ITU-T P.1301]: A meeting in which participants are located at least two locations and the communication takes place via a telecommunication system. The term telemeeting is used to emphasize that a meeting is often more flexible and interactive than a conventional business teleconference and could also be a private meeting. The telemeeting could be audio-only, audiovisual, text-based, or a mix of these modes.
+
+**3.1.2 conversational quality** [ITU-T P.1301]: The perceived quality when two or more test participants have a conversation.
+
+**3.1.3 two-party** [ITU-T P.1301]: Two persons. Example: Two persons are participating in a telemeeting, having a conversation, performing a test task together, etc. If not explicitly stated differently, two-party implicates that the persons are at two locations.
+
+**3.1.4 multiparty** [ITU-T P.1301]: More than two persons. Example: More than two persons are participating in a telemeeting, having a conversation, performing a test task together, etc. The term multiparty does not specify if the persons are distributed across two or more locations. If not explicitly stated differently, multiparty implicates that the persons are at two or more than two locations. When further specification is necessary, additional terms will be used (see point-to-point and multi-point) or the number of locations will be explicitly stated.
+
+**3.1.5 point-to-point** [ITU-T P.1301]: Two locations. Example: A multiparty point-to-point telemeeting means that more than two interlocutors are taking part, and the interlocutors are at exactly two locations. That means that in one location more than one interlocutors are present, as there are more than two persons.
+
+**3.1.6 multi-point** [ITU-T P.1301]: More than two locations. Example: A multiparty multi-point telemeeting means that more than two interlocutors are taking part, and the interlocutors are located across more than two locations. Multi-point does not specify if one or more than one interlocutor may be present at each location. In the special case that only one person is present at each location, the term one-per-site will be used.
+
+**3.1.7 one-per-site** [ITU-T P.1301]: One person per connected location. Example: In a multiparty one-per-site telemeeting more than two sites are connected with only one person present at each site.
+
+**3.1.8 conversation analysis (CA)** [b-Sacks, 1974]: The study of social interaction, in particular focusing on conversations.
+
+**3.1.9 turn construction unit (TCU)** [b-Sacks, 1974]: A conversation analysis term describing the fundamental segment of speech in a conversation – essentially a piece of speech that constitutes an entire 'turn'.
+
+**3.1.10 transition relevance place (TRP)** [b-Sacks, 1974]: A conversation analysis term which indicates where a turn or floor exchange can take place between speakers.
+
+**3.1.11 system effectiveness** [ITU-T P.1312]: The ratio, expressed as a percentage, between the performance score achieved on a given system and the performance score obtained in face-to-face communication.
+
+## **3.2 Terms defined in this Recommendation**
+
+This Recommendation defines the following terms:
+
+**3.2.1 choral behaviour:** Many people doing the same thing at the same time.
+
+**3.2.2 phatic expression:** An expression whose function is part of social interaction rather than to convey information.
+
+# **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+CA Conversation Analysis
+
+MOS Mean Opinion Score
+
+QoE Quality of Experience
+
+QoS Quality of Service
+
+TCU Turn Constructional Unit
+
+TRP Transition Relevance Place
+
+# **5 Conventions**
+
+None.
+
+# **6 Existing Recommendations concerning the subjective quality evaluation in case of pure transmission delay**
+
+In the following existing Recommendations on audio delay, video delay and audio-video synchronization the current understanding is outlined. These Recommendations have been developed for two-party interaction only. The multi-party case needs further study to ensure their applicability.
+
+## **6.1 Audio delay**
+
+Recommendation [ITU-T G.114] states that,
+
+"Regardless of the type of application, it is recommended to not exceed a one-way delay of 400 ms for general network planning..."
+
+"Although a few applications may be slightly affected by end-to-end (i.e., "mouth-to-ear" in the case of speech) delays of less than 150 ms, if delays can be kept below this figure, most applications, both speech and non-speech, will experience essentially transparent interactivity."
+
+The delay values in [ITU-T G.114] are based on the effect of pure audio delay only, i.e., in the complete absence of any echo. It is well-known that if echo is present, longer audio delays become easier detectable and much more disturbing. Effects of talker echo at different one-way echo-path delays are further described in [ITU-T G.131].
+
+## **6.2 Video delay**
+
+Most investigations regarding quality impact of delay have been performed regarding audio delays, but in an earlier version of [ITU-T G.114] (02/96), in clause B.2.3, it is mentioned that:
+
+"Tests were performed to assess the interaction between delay and user applications. In these tests a comparison of telephone conversations with videophone were made and it was shown that there is little difference between both types of connection."
+
+This result was obtained for synchronized audio and video. Some research has been performed looking at pure audio-visual delay in an interactive setting, but there is a need for more research to clearly confirm the recommendations of [ITU-T G.114] for this case, especially regarding multi-party communication.
+
+## 6.3 Synchronization between audio and video
+
+The limits within which audio and video are perceived to be synchronized are well examined, at least for TV screens. According to [ITU-R BT.1359-1],
+
+"subjective evaluations show that detectability thresholds are about +45 ms to -125 ms and acceptability thresholds are about +90 ms to -185 ms on the average, a positive value indicates that sound is advanced with respect to vision".
+
+As video encoding usually requires more time than audio coding, audio should generally be delayed to obtain audio-video synchronization [b-Berndtsson, 2012]. It is likely that it is easier to identify audio-video asynchrony as a technical issue than synchronous delay. Following from this, audio-video asynchrony will most likely be reflected more critically in mean opinion score (MOS) ratings.
+
+Low video frame rates and video frame rate jitter can influence the impression of audio-video synchronization.
+
+# 7 Conversation features
+
+## 7.1 Two-party and multi-party conversations
+
+There are differences between two-way conversations and multi-party conversations. For instance in multi-party conversations:
+
+- participants are likely to spend a greater proportion of the time listening rather than talking. Usually this will vary as the discussion proceeds, with talkers being more active or passive at different times;
+- telemeeting systems do not always attempt to reproduce the exact signals from the sending end at the receiving end; system designers are usually more interested in creating an environment where participants can interact effectively, and this can involve multiple technologies such as spatial audio, level compensation, noise reduction etc.;
+- participant interaction is more complicated: in a two-party conversation the role of the speaker and the listener simply alternate, whereas in a multi-party conversation, the next speaker could be any one of several current listeners;
+- passive participants are not only listening to what the active participants are saying, they are listening to the active participants interacting.
+
+## 7.2 Two analysis techniques
+
+In this Recommendation two different techniques for analysing a conversation are discussed. The first is based on the linguistic discipline of conversation analysis (CA) [b-Sacks, 1974] and focuses on analysing how the participants interact. For evaluating the impact of delay, the two most relevant analysis concepts from CA are turn-taking (see clause 7.3) and backchannels (see clause 7.6).
+
+The second technique analyses patterns of the temporal occurrence of utterances without labelling their purpose. This approach does not rely on the content of the utterances and can therefore be
+
+built on voice activity detection algorithms. This approach is referred to as conversational surface structure analysis (clause 7.4) and was pioneered by Brady in the 1960s. [b-Brady, 1965].
+
+## 7.3 Conversation analysis and turn-taking
+
+In a free conversation the organization of the conversation, in terms of who speaks when, is referred to as 'turn-taking'. This is implicitly negotiated by a multitude of verbal cues within the conversation and also by nonverbal cues such as physical motion and eye contact. Turn-taking behaviour is more-or-less universal, even across languages of very different structures. This behaviour has been extensively studied in the discipline of conversation analysis, for example, [b-Sacks, 1974].
+
+Some useful concepts from CA are:
+
+- The turn constructional unit (TCU), which is the fundamental segment of speech in a conversation – essentially a piece of speech that constitutes an entire 'turn'. TCUs are primarily determined as being pragmatically or grammatically complete utterances. That is, have they served a specific purpose, or are they syntactically complete. Typically they are separated by short pauses and a falling tone.
+- The transition relevance place (TRP), which indicates where a turn or floor exchange can take place between speakers. TCUs are separated by TRPs.
+- Turn allocation component, which relates to who should speak next. This is done either explicitly when the current talker selects the next talker – directly or subtlety; or the next talker 'self-selects' by simply interrupting at the end of the TCU.
+
+These processes enable the basic turn-taking process to take place, as described in [b-Sacks, 1974] and shown in a slightly modified form in Figure 1. As a TCU comes to an end the first decision to take place is, has the current talker selected the next talker? If so, the designated new talker usually feels obliged to talk. Otherwise, any participant including the current talker will self-select; a process which generally works by the first person to speak gaining the right to the next turn. The result of this process is a well ordered conversation as illustrated in Figure 2.
+
+![Flowchart of the conversation turn-taking process. It starts with '1. TCU', followed by '2. Current talker selects the next talker?'. If 'Yes', it loops back to '1. TCU'. If 'No', it goes to '3. Next talker self-selects?'. If 'Yes', it loops back to '1. TCU'. If 'No', it goes to '4. Current talker continues?'. If 'Yes', it loops back to '1. TCU'. If 'No', it loops back to the entry point of step 3. The diagram is labeled 'P.1305(16)_F01'.](d4af765160d04ecef538e5066006dc77_img.jpg)
+
+```
+
+graph TD
+    1[1. TCU] --> 2{2. Current talker selects the next talker?}
+    2 -- Yes --> 1
+    2 -- No --> 3{3. Next talker self-selects?}
+    3 -- Yes --> 1
+    3 -- No --> 4{4. Current talker continues?}
+    4 -- Yes --> 1
+    4 -- No --> 3
+  
+```
+
+Flowchart of the conversation turn-taking process. It starts with '1. TCU', followed by '2. Current talker selects the next talker?'. If 'Yes', it loops back to '1. TCU'. If 'No', it goes to '3. Next talker self-selects?'. If 'Yes', it loops back to '1. TCU'. If 'No', it goes to '4. Current talker continues?'. If 'Yes', it loops back to '1. TCU'. If 'No', it loops back to the entry point of step 3. The diagram is labeled 'P.1305(16)\_F01'.
+
+**Figure 1 – The conversation turn-taking process**
+
+![Timeline diagram showing turn-taking between three talkers (A, B, and C). Talker A has four TCU blocks, with TRP blocks above the first three. Talker B has four TCU blocks, with TRP blocks above the first two and last two. Talker C has one TCU block, with a TRP block above it. The diagram is labeled 'P.1305(16)_F02'.](042733dc5e8e7f5f30b60adba3266cde_img.jpg)
+
+Timeline diagram showing turn-taking between three talkers (A, B, and C). Talker A has four TCU blocks, with TRP blocks above the first three. Talker B has four TCU blocks, with TRP blocks above the first two and last two. Talker C has one TCU block, with a TRP block above it. The diagram is labeled 'P.1305(16)\_F02'.
+
+**Figure 2 – Example of turn-taking in a well-ordered conversation**
+
+Note of course that most of the turn-taking process is carried out subconsciously in line with what the participants consider to be appropriate behaviour. Knowing when it is acceptable to take your turn in a conversation is usually learned from an early age and becomes an important social skill.
+
+Depending on the type of conversation, there may also be a significant amount of talking taking place outside the underlying turn-taking process – in some cases obscuring it completely. This can include backchannels (clause 7.5), brief side-conversations, corrections, confirmations and choral laughter.
+
+Note that this description of the turn-taking process excludes interruptive behaviour. From a CA perspective, a participant starting a turn at a time other than a TRP is making a 'violative interruption'. This can often be interpreted by other participants as ill-mannered or rude behaviour.
+
+This turn-taking decision process leads to the following meeting characteristics:
+
+- Overwhelmingly, only one participant talks at a time [b-Sacks, 1974].
+- Occurrences of more than one talker at a time are common, but brief [b-Sacks, 1974].
+- Transitions from one turn to the next, with no gap or overlap are common. Together with transitions characterized by either a slight gap or slight overlap, they make up the vast majority of transitions [b-Sacks, 1974].
+- The most frequent gaps between talkers are in the region of 200 ms. [b-Gisladottir, 2015]. Gaps of more than 1 second are rare but do occur. [b-Jefferson, 1989]
+
+## 7.4 Conversation structure and styles
+
+Conversations can vary dramatically in their style of structure. At one extreme relaxed free conversation can occur amongst friends in social situations, where all turn taking is organized as described above. There may also be a significant amount of talking taking place outside the underlying turn-taking process, in some cases obscuring it completely. This additional content can include backchannels (clause 7.5), brief side-conversations, corrections, confirmations and choral laughter.
+
+At the other extreme some conversations are highly structured where most turn-taking is explicitly directed by a chairman or moderator. In this case a participant is directly asked by the participant currently holding the turn to speak.
+
+A conversation can change style dynamically, e.g., following an agenda but breaking out to free conversations in the discussion of single items.
+
+## 7.5 Backchannels and other behaviours during conversations
+
+A further aspect to consider is that there is often a lot of talking taking place outside the formal turn-taking process as described in CA. A conversation feature of particular interest is the use of continuers or backchannels [b-OConnail, 1993], also referred to as 'continuers' or 'listener responses' [b-Knapp, 2010]. These are listener responses in a primarily one-way communication, commonly used by participants in a conversation as a sign of acknowledgement and also to signal to the talker to continue with their turn. These can be both verbal and non-verbal in nature (e.g., "yeah", "mm", "uh-huh", "mm-hmm") and are frequently phatic expressions. They are often made between sentences and especially at transition points. Backchannels can also be visual in the form of nods or other facial expressions.
+
+The term "backchannel" was designed to imply that there are two channels of communication operating simultaneously during a conversation; the predominant channel is that of the speaker who directs primary speech flow.
+
+Other behaviours include: requests for confirmation or clarification; choral behaviour, especially laughter; and side conversations between subgroups. In many situations, particularly informal ones, it is not unusual to have several conversations taking place simultaneously with participants both talking and listening at the same time. Thus the ability of a telemeeting system to support doubletalk is a very important feature for natural human communications.
+
+## 7.6 Conversation surface structure analysis
+
+Conversation surface structure analysis has been introduced by Brady [b-Brady, 1965], [b-Brady, 1968], [b-Brady, 1971]. It analyses the temporal occurrence of speech activity, that is, on-off patterns of speech and uses this to define various conversation states such as single-talk, multiple-talk. These are then analysed to provide metrics such as:
+
+- State sojourn time: the mean time of staying in that state, [b-Brady1971]
+- Speaker alteration rate: the mean rate at which speaker changes occurred [b-Hammer, 2004])
+
+- Utterance Rhythm: mean time from one utterance of a speaker to its next utterance, [b-Schoenenberg, 2014].
+
+Conversation surface structure analysis consists of the following procedure:
+
+1. A voice activity algorithm can be used to extract those on-off patterns of each single person recording. See for example Figure 3, top panel.
+2. Then for each site, the single person on-off patterns need to be combined as they were experienced by the persons at the different ends which means the respective other persons need to be delayed if delay was present. See for example Figure 3, bottom panel.
+3. In the next step, states need to be assigned to every sample of the combined on-off pattern, according to Figure 4. In this case 'S' and 'M' are used to indicate single and multiple talker states, and sub-scripts 'n,X' to indicate how many talkers there are and which one is talking. Thus for two participants.  $S_{2,0}$ : silence,  $S_{2,A}$ : single talk of person A,  $S_{2,B}$ : single talk of person B,  $M_{2,AB}$ : multi/double talk of persons A and B. State transitions are indicated by arrows.
+4. From those states, it is possible to compute the measures such as state sojourn time, speaker alteration rate and utterance rhythm that characterize the conversation surface structure.
+
+An example of how to do this is given in clause 10.
+
+![Figure 3: Two horizontal timelines showing speech activity for Person A and Person B. The top panel shows a situation without delay, where Person A's speech (black blocks) and Person B's speech (grey blocks) overlap directly. The bottom panel shows a situation with delay, where Person B's speech is shifted to the right relative to Person A's. Below the timelines, state labels are placed in intervals: S_{2,A}, M_{2,AB}, S_{2,B}, S_{2,0}, S_{2,A}, S_{2,0}, S_{2,B}. The label 'P.1305(16)_F03' is in the bottom right corner.](411fa16c3211377525ba37c57784fee0_img.jpg)
+
+Figure 3: Two horizontal timelines showing speech activity for Person A and Person B. The top panel shows a situation without delay, where Person A's speech (black blocks) and Person B's speech (grey blocks) overlap directly. The bottom panel shows a situation with delay, where Person B's speech is shifted to the right relative to Person A's. Below the timelines, state labels are placed in intervals: S\_{2,A}, M\_{2,AB}, S\_{2,B}, S\_{2,0}, S\_{2,A}, S\_{2,0}, S\_{2,B}. The label 'P.1305(16)\_F03' is in the bottom right corner.
+
+**Figure 3 – Example of single and multi talk states in a two-party conversation situation.**  
+**Top panel: Situation without delay. Bottom panel: Situation from the perspective of Person A when delay is present, i.e., person B is delayed**
+
+![Figure 4: A state transition diagram for a two-party conversation. It consists of four circular nodes arranged in a diamond shape: S_{2,0} at the top, S_{2,A} on the left, S_{2,B} on the right, and M_{2,AB} at the bottom. Arrows indicate transitions: S_{2,0} to S_{2,A}, S_{2,0} to S_{2,B}, S_{2,A} to M_{2,AB}, S_{2,B} to M_{2,AB}, M_{2,AB} to S_{2,A}, and M_{2,AB} to S_{2,B}. A vertical double-headed arrow connects S_{2,0} and M_{2,AB}. The label 'P.1305(16)_F04' is in the bottom right corner.](1b5a812c8aa20fd5cba28e97001d32de_img.jpg)
+
+Figure 4: A state transition diagram for a two-party conversation. It consists of four circular nodes arranged in a diamond shape: S\_{2,0} at the top, S\_{2,A} on the left, S\_{2,B} on the right, and M\_{2,AB} at the bottom. Arrows indicate transitions: S\_{2,0} to S\_{2,A}, S\_{2,0} to S\_{2,B}, S\_{2,A} to M\_{2,AB}, S\_{2,B} to M\_{2,AB}, M\_{2,AB} to S\_{2,A}, and M\_{2,AB} to S\_{2,B}. A vertical double-headed arrow connects S\_{2,0} and M\_{2,AB}. The label 'P.1305(16)\_F04' is in the bottom right corner.
+
+**Figure 4 – Possible states (sets and subsets) for a two-party conversation situation**
+
+# 8 The impact of delay
+
+## 8.1 Turn-taking with delay
+
+From a conversation analysis perspective, the impact of delay in a conversation is primarily to disrupt the turn-taking process because each participant has a different understanding of when the TRP occurs. A new talker may believe they are starting to talk at the TRP, but the other participants will hear them sometime later when they themselves may have already started talking. This breaks the self-selection process described in clause 7.3 because the participants cannot be aware of who started talking first. Essentially, none of the participants is able to interrupt at the TRP experienced by the other participants, and if the delay is long both talkers interpret the others action as a violative interruption.
+
+Note that the participants may not realize that the confusion they are experiencing is due to transmission delay, often attributing it to aberrant behaviour of the other participants, for example, slow responding or even rudeness.
+
+A good example of this delay induced confusion is the 'false start'. These are delay induced conversation features that occur when two participants start talking simultaneously after a period of silence or in response to a stimulus from another participant. For example, in a multi-party conversation this can occur in response to a question from a third participant as shown in Figure 5. Once they realize somebody else is also talking, one of three things can happen:
+
+1. Both participants stop talking. This could be interpreted as two simultaneous unintended successful interrupts. More false starts can then follow in an attempt to correct the false-start, possibly involving other participants, leading to a short period of confusion as to who actually has the conference 'floor'. From a CA point of view this has a major impact since the conversation stops unexpectedly.
+2. One participant stops talking and the other continues. Whilst this is probably the least disruptive on conversation flow, it can still be a significant disruption of the information exchange; the participant who stopped talking may have been making a more useful contribution than the participant who continued. It has also provided a significant distraction from the matter under discussion.
+3. Both participants keep talking resulting in a longer period of multi-talk. Whilst the conversation still continues, the impact on intelligibility is severe and from a social point of view the behaviour of the participants can be perceived as rude or inappropriate.
+
+False starts are common in multi-party telemeetings where delay is present. However normal conversation turn-taking makes them less likely in two-way conversations. Of course two participants can start talking simultaneously even if there is no delay. However, delay appears to make the problem worse because it takes longer for the situation to become apparent to the participant.
+
+![Figure 5: False starts in 3-way conversation. A timeline diagram showing talk and listen states for Person A, B, and C. It illustrates three cases of false starts: Case 1 (B and C stop, leading to confusion), Case 2 (B continues, C stops, least disruptive), and Case 3 (both continue, resulting in multi-talk and reduced intelligibility).](ad29805cd4f64ad2828e14feb66de664_img.jpg)
+
+Figure 5 illustrates false starts in a 3-way conversation between Person A, B, and C. The diagram shows talk and listen states over time. Dashed lines connect talk periods of one person to listen periods of another. The diagram is divided into three cases:
+
+- Case 1:** Both B and C stop, leading to period of confusion.
+- Case 2:** B continues, C stops. This is the least disruptive case.
+- Case 3:** Both B and C continue, resulting in a period of multi-talk and reduced intelligibility.
+
+P.1305(16)\_F05
+
+Figure 5: False starts in 3-way conversation. A timeline diagram showing talk and listen states for Person A, B, and C. It illustrates three cases of false starts: Case 1 (B and C stop, leading to confusion), Case 2 (B continues, C stops, least disruptive), and Case 3 (both continue, resulting in multi-talk and reduced intelligibility).
+
+**Figure 5 – False starts in 3-way conversation**
+
+## 8.2 Conversation surface structure and delays
+
+It has been shown in many studies e.g., [b-Brady, 1971], [b-Egger, 2012], that the conversation flow is disrupted by delays. In particular, it has been described in different works [b-Brady, 1971], [b-Schoenenberg, 2014] that the quality of the conversational experience compared to a face-to-face conversation diverges in terms of conversational realities of each telemeeting participant, and that the degree of divergence is dependent on the length of the delay [b-Schoenenberg, 2014]. The higher the degree of divergence, the more difficult it will be for participants to hold a fluent interaction without misunderstandings or breakdowns of the interactional flow.
+
+An example of a conversation part with high divergence can be found in Figure 6.
+
+![Figure 6: Example of conversation part with high degree of divergence between the two realities due to latency. A timeline diagram showing states (SI, BR, AS, NI) for Person A and Person B. It shows how latency leads to different perceived states for each participant.](fc857414626a8d94d132e12d9afe52a4_img.jpg)
+
+Figure 6 shows a conversation part with high divergence due to latency. The diagram illustrates states (SI, BR, AS, NI) for Person A and Person B. The states are shown for both participants' own and other realities. The diagram shows how latency leads to different perceived states for each participant.
+
+P.1305(16)\_F06
+
+Figure 6: Example of conversation part with high degree of divergence between the two realities due to latency. A timeline diagram showing states (SI, BR, AS, NI) for Person A and Person B. It shows how latency leads to different perceived states for each participant.
+
+**Figure 6 – Example of conversation part with high degree of divergence between the two realities due to latency**
+
+Here it can be seen that owing to the delay the number of states has increased from the four states defined in clause 7.6, to include breaks (BR), alternating silence (AS), successful interruption (SI)
+
+non-successful interruption (NI). An explanation of how the degree of divergence figure can be calculated is given in clause 10.3.
+
+## 8.3 Multiparty and two-party conversations with delay
+
+So far there is only little research on multiparty conversations and delay; most research conducted has focused on the two-party case. However, it is likely the impact of delays will be different in multi-party conversations for the following reasons:
+
+- Participants are likely to spend a greater proportion of the time listening rather than talking. This will vary as the discussion proceeds, with talkers being more active or passive.
+- Active participants, those actively contributing to the discussion, have shown to be more sensitive to delay compared to their non-active fellow participants [b-Schmitt, 2014a], [b-Schoenenberg, 2011].
+- The turn-taking process is more complicated. For example, in a two-party conversation the role of the speaker and the addressee alternate. In multi-party conversations, the speaker can have multiple addressees and listeners and thus more responders. A greater likelihood of false starts or passive interruptions can thus be expected.
+
+## 8.4 Other side-impacts of delay
+
+Delay can also impact the performance of the system, for example, it can affect jitter buffers and result in packet loss which in turn can lead to audible artifacts.
+
+# 9 Factors influencing the impact of pure delay
+
+In clause 7, it was noted that conversations can differ greatly in their structure, ranging from formal meetings with strict control, up to very informal social gatherings, and that the impact of delay will differ in each case. In this section other factors that influence the impact of delay are considered.
+
+## 9.1 Audiovisual telemeetings
+
+The previous clauses have primarily discussed the audio-only meetings. In the case of synchronized audiovisual telemeetings there are the following differences:
+
+- Delay is more obvious to non-naive participants since visual reactions are seen.
+- Visual cues (e.g., gestures, nods, gaze) are available to support turn-taking and back-channel communications.
+- The video provides additional information that helps the conversation organization. For example, participants can make visual signals to each other: e.g., raising hand to interrupt, collective voting.
+
+Subjective tests have shown that it is more important to synchronize audio and video than to keep the one-way audio transmission delay as low as possible [b-Berndtsson, 2012]. Since video is usually more delayed than audio, the audio should generally be delayed to obtain audio-video synchronization, at least for transmission delays below 600 ms. The audio should not be more than 90 ms ahead of the video, and also less than 185 ms after the video. This reflects the natural experience of light travelling faster than sound [ITU-R BT.1359-1].
+
+A study [b-Tam, 2012] comparing two-party conversations with audio and audiovisual channels, found that perceived conversation naturalness was significantly impacted at a delay of 400 ms for audio-only connections and at 500 ms for audio-visual connections. Similar insights were drawn from studies comparing face-to-face, audio-only and audiovisual meeting [b-Tang, 1992]. In audiovisual meetings longer silences were observed but the subjective scores from the participants did not reflect this.
+
+## 9.2 User expectations
+
+Whilst user expectations will have little impact on the effect of delay in a telemeeting, users are likely to be more accepting of delays under some conditions. For example they will have lower expectations from lower cost services or when making calls on more challenging situations.
+
+The physical distance also adds to the delay and users are usually aware of this. For example, signals propagate through physical media at approximately 2/3 of the speed of light, so it takes about 50 ms to travel 10,000 km. Therefore expectations might be lower when talking to someone on the other side of the world than when talking to someone in the office next door.
+
+## 9.3 Asymmetric delay between participants and co-location
+
+Usually, there will be different delays in the connections to each site. In this situation, test participants experiencing longer delays will have more difficulties taking part in the conversation. This can have the knock-on effect of reducing the quality of the whole group experience. It can, for example, cause a disruption of the conversation flow, or as it has been shown [b-Schmitt, 2014b], a single delayed person can cause a worse experience for all participants in a five party telemeeting.
+
+A similar situation will occur if many participants are co-located and only a few are joining over a delayed connection.
+
+## 9.4 Interpersonal influences
+
+The sensitivity for delay can be influenced by the participant's expectations of the other participants. It can be difficult for participants to determine whether an apparently slow response is due to the system or to a genuine slow response. To a certain extent the degree of familiarity with the other participant can influence this based on previous interactions with them.
+
+However, it has been shown that conversation partners that know each other can be perceived to be unusually slow if there are long delays [b-Berndtsson, 2012]. Furthermore, persons that know each other well often have more spontaneous conversations, which can also make delays more detectable. Note that even though interruption may be a part of the normal conversations in this case, they do not occur with awkward timing or too often.
+
+The social role of the interlocutors and their corresponding interaction behaviour can also have an impact. For instance, a dominant person, the boss or mentor, may speak more and may ask more questions within a call. If this is the case, response times will appear to be long for the asking person but short for the responding person, which leads to different perceptions for the different sites.
+
+# 10 Testing methods
+
+## 10.1 General comments
+
+It is recommended to carry out the subjective quality evaluation of multiparty telemeetings as much as possible according to existing test methods recommended by ITU-T.
+
+Since the primary impact of delay is on group interaction, it will be necessary to use some form of conversation in the test. This could include multi-party conversation tests or third party listening tests where subjects listen and comment on the quality of a conversation between others.
+
+Tests on group inter-action can be divided into several types:
+
+- conversational-opinion tests;
+- group inter-action tests based on conversation analysis and conversation surface structure analysis;
+
+- tests that measure group performance when undertaking tasks;
+- micro-feature tests such as the task efficiency tests described in [ITU-T P.1312] which focus on a specific aspect of talker interaction such as double-talk or turn-taking.
+
+It is possible to design tests that include elements of more than one of these types.
+
+## 10.2 Conversational-opinion tests
+
+General procedures for these are laid down in Annex D of [ITU-T P.1301]. The test must allow the subjects to experience the problem and report its impact in terms of conversation difficulty.
+
+### 10.2.1 Training session
+
+In most cases, the test procedure will include a short training phase to familiarize the subjects with the system and the test task. This is important if the subjects do not know each other well in order to encourage more interactive conversations. This could be incorporated into an introduction session if appropriate and consist of a simple interactive game or task to learn each other names and to generally 'break the ice'.
+
+### 10.2.2 Conversational test tasks
+
+The test tasks should ideally be delay sensitive, but support natural conversation. Some suggestions for appropriate tasks are given in Annex D of [ITU-T P.1301] and in Annex A. More specifically:
+
+- Free conversation tasks are recommended for studying group behaviour since they allow natural subject interaction and subjects are able to adapt their behaviour to make the best use of the system under test.
+- Short conversation tests (SCTs) as described in [ITU-T P.805] are not delay sensitive because subjects have to read from a script which masks the delay [b-Berndtsson, 2012].
+- Highly interactive tasks such as random number exchanges are sensitive to delay, but do not reflect normal conversation behaviour.
+- Delays can be more easily detected as a technical issue in a highly interactive conversation where the motivation to interact fast is high [b-Schoenenberg, 2014]. As an example, some kind of competition might motivate subjects to interact more efficiently, and delays may be more apparent if they are hindering the interaction.
+
+### 10.2.3 Test questions
+
+Care should be used in the choice of questions in order to enable the test subjects to appropriately comment on their experience. For example, questions based on how the subjects perceived the interactivity are likely to be more revealing than questions about the overall quality.
+
+For example:
+
+- Did you experience difficulty in communicating?
+- How would you judge the effort required to interrupt the other participants?
+- How easy did you find it to communicate using the system?
+- How attentive were your conversation partners during the call?
+
+A number of appropriate examples are given in [ITU-T P.805] and Annex D of [ITU-T P.1301], along with accompanying scales.
+
+Because delay induced interrupts are sometimes perceived as rude it would be good if these perceptions could also be captured. This can be difficult since subjects may object to their individual personalities being scrutinised in this manner. Perhaps the best approach, if the subjects knew each other well, is to ask questions such as, "Did the behaviour of any of the other participants seem out of character at any time?"
+
+## 10.3 Group interaction tests
+
+The principle behind group interaction tests lies in a comparison between the behaviour of test subjects in a reference condition, with their behaviour when using the system under test.
+
+Of the two approaches discussed earlier, conversation analysis, and conversation surface structure analysis, the latter is more mature and its focus on simply who is talking at any given time, lends itself more to an algorithmic approach [b-Schoenenberg, 2014]. Because conversation analysis assumes an understanding of the actual conversation content, detailed analysis is likely to require higher level resources such as speech recognition and natural language processing. Consequently at this stage no measurement techniques directly based on it have been published. However, analysis based on simple turn-taking could be considered.
+
+In group interaction tests, in addition to normal good practice in subject selection [ITU-T P.1301], [ITU-T P.800], careful consideration should be given to matching test subject profiles. This is important for free conversations since as far as possible we need to ensure consistent behaviour across groups.
+
+The number of variables in free conversations that influence conversational interaction can be very large. The interactivity in the conversation might be higher or more consistent if the test subjects have:
+
+- The same first language.
+- A similar level of experience in using telemeeting systems.
+- Similar levels of familiarity with each other.
+- Similar cultural backgrounds.
+
+It may also be appropriate to consider matching ages, but of course, note that excessive restrictions placed on subject selection will reduce the generality of the results.
+
+### 10.3.1 Conversation surface structure measurements
+
+It can be seen from clause 8.2 that the quality of the conversational experience compared to a face to face conversation diverges in terms of conversational realities of each telemeeting participant, and that the degree of divergence is dependent on the length of the delay [b-Schoenenberg, 2014]. A measure of this divergence can be calculated using the following procedure, and with reference to Figure 6:
+
+1. First of all, the most used meaningful state walks needs to be defined, that are:  
+BR: Break – After a single talk period of one person, a silent period follows, after which single talk of the same person continues.  
+AS: Alternating silence – After a single talk period of one person, a silence follows, after which single talk of a different person continues.  
+NI: Non-successful interruption – After a single talk period of one person, double talk or multi talk (e.g., triple talk) follows, after which single talk of the same person continues.  
+SI: Successful interruption – After a single talk period of one person, double talk or multi talk (e.g., triple talk) follows, after which single talk of a different person who has started to talk in the double/multi talk period continues.
+2. Compute for each person a speaker state pattern using the conversation surface structure analysis paradigm (clause 7.4) as it was experienced by the persons at the different ends which means the respective other persons need to be delayed if delay was present. See Figure 6.
+3. Based on the state pattern, state walks can be detected. For each walk detected in i.e., the conversational reality of person A it is then looked into the same walk at the reality of person B to see how person B experience this walk. The origin for each walk is always a
+
+single talk period. When looking at person A's reality e.g. single talk of person A, followed by a silence, followed by single talk of person A, this will be noted as a break by person A in A's reality. In case of two interlocutors, eight different kinds of walks can occur, the four types listed above, starting with either person A or person B in single talk:
+
+| State walk | Description                                             | States transitions (see Figure 4)                  | Speaker turn |
+|------------|---------------------------------------------------------|----------------------------------------------------|--------------|
+| BR.AA      | Break, starting and ending with A                       | $S_{2,A} \Rightarrow S_{2,0} \Rightarrow S_{2,A}$  | No           |
+| BR.BB      | Break, starting and ending with B                       | $S_{2,B} \Rightarrow S_{2,0} \Rightarrow S_{2,B}$  | No           |
+| AS.AB      | Alternating silence, starting with A, ending with B     | $S_{2,A} \Rightarrow S_{2,0} \Rightarrow S_{2,B}$  | Yes          |
+| AS.BA      | Alternating silence, starting with B, ending with A     | $S_{2,B} \Rightarrow S_{2,0} \Rightarrow S_{2,A}$  | Yes          |
+| NI.AA      | Non-successful interruption, starting and ending with A | $S_{2,A} \Rightarrow M_{2,AB} \Rightarrow S_{2,A}$ | No           |
+| NI.BB      | Non-successful interruption, starting and ending with B | $S_{2,B} \Rightarrow M_{2,AB} \Rightarrow S_{2,B}$ | No           |
+| SI.AB      | Successful interruption, starting with A, ending with B | $S_{2,A} \Rightarrow M_{2,AB} \Rightarrow S_{2,B}$ | Yes          |
+| SI.BA      | Successful interruption, starting with B, ending with A | $S_{2,B} \Rightarrow M_{2,AB} \Rightarrow S_{2,A}$ | Yes          |
+
+Similarly, such state walks can be computed for multiparty scenarios. Here examples for a three-party call for state walks starting with person A:
+
+| State walk | Description                 | States transitions (see Figure 4)                                                                                                                                                                    | Speaker turn |
+|------------|-----------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------|
+| BR.AA      | Break                       | $S_{3,A} \Rightarrow S_{3,0} \Rightarrow S_{3,A}$                                                                                                                                                    | No           |
+| AS.AB      | Alternating silence         | $S_{3,A} \Rightarrow S_{3,0} \Rightarrow S_{3,B}$                                                                                                                                                    | Yes          |
+| AS.AC      | Alternating silence         | $S_{3,A} \Rightarrow S_{3,0} \Rightarrow S_{3,C}$                                                                                                                                                    | Yes          |
+| NI.AA      | Non-successful interruption | $S_{3,A} \Rightarrow M_{3,AB} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,A}$<br>or: $S_{3,A} \Rightarrow M_{3,AC} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,A}$ | No           |
+| SI.AB      | Successful interruption     | $S_{3,A} \Rightarrow M_{3,AB} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,B}$<br>or: $S_{3,A} \Rightarrow M_{3,AC} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,B}$ | Yes          |
+| SI.AC      | Successful interruption     | $S_{3,A} \Rightarrow M_{3,AB} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,C}$<br>or: $S_{3,A} \Rightarrow M_{3,AC} (\Leftrightarrow M_{3,ABC} \Leftrightarrow) \Rightarrow S_{3,C}$ | Yes          |
+
+In the next step the first period of single talk of a detected walk in one person's reality is searched in the other persons' reality and the walk that is found there is noted. It can be the same kind of walk or a different one. In this way, the number of matching walks and mismatching walks can be counted. A convenient approach for this is to use a confusion matrix as shown below: the rows represent the walks found in the "own" reality of a person, e.g., person A; the columns represent the walks found in the reality of the other person, e.g., person B; and the matrix elements contain the counts. In such a matrix, the diagonal represents the matching walks (indicated with  $\bullet$ ), all other matrix elements represent the non-matching walks (indicated with  $\times$ ).
+
+|                     |       | Reality of person B |       |       |       |       |       |       |       |
+|---------------------|-------|---------------------|-------|-------|-------|-------|-------|-------|-------|
+|                     |       | BR.AA               | BR.BB | AS.AB | AS.BA | NI.AA | NI.BB | SI.AB | SI.BA |
+| Reality of person A | BR.AA | ●                   | ×     | ×     | ×     | ×     | ×     | ×     | ×     |
+|                     | BR.BB | ×                   | ●     | ×     | ×     | ×     | ×     | ×     | ×     |
+|                     | AS.AB | ×                   | ×     | ●     | ×     | ×     | ×     | ×     | ×     |
+|                     | AS.BA | ×                   | ×     | ×     | ●     | ×     | ×     | ×     | ×     |
+|                     | NI.AA | ×                   | ×     | ×     | ×     | ●     | ×     | ×     | ×     |
+|                     | NI.BB | ×                   | ×     | ×     | ×     | ×     | ●     | ×     | ×     |
+|                     | SI.AB | ×                   | ×     | ×     | ×     | ×     | ×     | ●     | ×     |
+|                     | SI.BA | ×                   | ×     | ×     | ×     | ×     | ×     | ×     | ●     |
+
+In case of a multiparty scenario, this confusion matrix is extended with the additional state walks and it is computed for each pair of the reality of two persons.
+
+Then, from each such confusion matrix between two persons X and Y, the total number of matching and non-matching walks can be computed:  $\text{numMatch\_XY} = \text{sum of counts in the diagonal elements}$   $\text{numMismatch\_XY} = \text{sum of counts in all non-diagonal elements}$
+
+Finally, the number of mismatching walks needs to be related to the number of matching walks for building the parameter *divergence* [b-Schoenenberg, 2014], which is computed for each person using the corresponding confusion matrices.
+
+For the two-party scenario this leads to  $\text{Divergence\_A} = \text{Divergence\_B} = \text{numMismatch\_AB} / \text{numMatch\_AB}$
+
+For the three-party scenario this leads to:
+
+$\text{Divergence\_A} = (\text{numMismatch\_AB} + \text{numMismatch\_AC}) / (\text{numMatch\_AB} + \text{numMatch\_AC})$
+
+$\text{Divergence\_B} = (\text{numMismatch\_AB} + \text{numMismatch\_BC}) / (\text{numMatch\_AB} + \text{numMatch\_BC})$
+
+$\text{Divergence\_C} = (\text{numMismatch\_AC} + \text{numMismatch\_BC}) / (\text{numMatch\_AC} + \text{numMatch\_BC})$
+
+The divergence is small if conversational realities are similar and high if they are rather different.
+
+## 10.4 Communication system effectiveness tests
+
+System effectiveness refers to the time that is needed to achieve the goals of a conversation using a communication system, relative to the time taken in a face to face meeting. Transmission delays will reduce the system effectiveness, increasing the meeting time not just because of the increased delay, but also because of the impact of the delay on the conversation turn-taking described above.
+
+## 10.5 Micro-feature tests
+
+An example of a micro-efficiency test is the task efficiency test [ITU-T P.1312] which is specifically designed to measure how well a system supports discussions with high levels of multi-talk. Whilst not designed to measure delay performance, it is delay sensitive since good performance in multi-talk relies on good interactivity behaviour which is in turn influenced by delay. This is shown in Appendix 3 of [ITU-T P.1312].
+
+Other tests designed to focus on conversation features such as false starts or turn-taking can also be envisaged.
+
+# **11 Areas for further research regarding the impact of delay**
+
+There are many aspects of the impact of delay not yet fully understood and warrant further study. These include:
+
+- 1) The effects of asymmetric delay conditions between different participants in a telemeeting.
+- 2) The effects of varying delays in a telemeeting.
+- 3) Co-dependencies to other impairments such as echo, low frame rate, frame size.
+- 4) The relationship between the impact of delay and the features of different types of audio rendering.
+- 5) The impact of delay in relation to factors like the types of clients (screen size) and the number of participants using each client.
+- 6) The relationship between delay and spatial audio rendering.
+- 7) Analysis algorithms based on conversation analysis and/or turn-taking.
+
+## Annex A
+
+## Suggestions for free-conversation tasks
+
+(This annex forms an integral part of this Recommendation.)
+
+In [b-Berndtsson, 2012] it was noted that the best type of task for evaluating the impact of delay was a free conversation, where the subjects are free to express themselves in a natural manner, such as they would in normal life. However, it is also important to stimulate conversation of an appropriate style for the test. Typical conversation styles might include:
+
+- a. Relaxed, informal conversation.
+- b. Formal, 'business' style conversation.
+- c. Focused, problem solving discussion.
+
+A range of test tasks for audio conversational tests are described in [ITU-T P.800] and [ITU-T P.805], with further test tasks for audiovisual conversational tests are described in [ITU-T P.920]. However, these are primarily tasks suitable for two-way conversations and are not all suitable for extension to the multi-party situation. A range of tasks more appropriate for multi-party tests is given in Appendices III and V of [ITU-T P.1301].
+
+### A.1 'Holiday' task
+
+In this task the participants are asked to:
+
+- a. Create a list of features that their ideal holiday would include (5 minutes).
+- b. List them in order of importance (5 minutes).
+
+This task approach can be extended to include features of an ideal job, pastime, film, etc.
+
+Good points: A very good task for getting people involved in an informal type meeting – people like talking about experiences they enjoy.
+
+Poor points: It does not guarantee a balanced conversation – some participants could dominate or be too passive.
+
+### A.2 Role-playing games
+
+In this the test subjects take part in a role in a fictitious scenario. This is not a scripted test such as SCT, but relies on the test subjects taking on a role in a scenario. A good example of this is the "You be the Judge" game, (<http://www.amazon.co.uk/Paul-Lamond-You-Be-Judge/dp/B00422MKG4>) where the test subjects take on roles in a courtroom such as judge, council for the prosecution, defence, defendant, etc., and role play a series of scenarios in order to reach a solution.
+
+Good points: Stylistically this tends to replicate business type formal meetings.
+
+Poor points: Relies on subjects acting abilities and willingness to play a sufficiently active part.
+
+### A.3 "Who am I?" Celebrity Name-Guessing Task
+
+This task has been proposed in [b-Schoenenberg, 2014b] as a task for audiovisual communication with high delay sensitivity. In this task, participants are supposed to be a celebrity, and the task is to guess their own name.
+
+The task should not be confused with the *Name-Guessing Task* described in [ITU-T P.920]. The *Celebrity Name-Guessing Task* described here has strong social component due to the aspect that a participant is associated with a celebrity that he or she has to guess. In addition, the game character of this task let people find themselves in a joyful state, have fun and interact naturally.
+
+The game rules are described in [b-Schoenenberg, 2016] as follows:
+
+*Each participant receives a note with initials of a celebrity person that he or she has to guess. This note is clipped to the shirt of the person so that they and their interlocutor are reminded of it. The respective other knows the full name of the unknown celebrity person due to a hidden note with the full name. One participant begins by asking questions that can only be answered with "yes" or "no", for example, "Am I female?" or "Am I a movie star?". As long as the response of the other one is "yes" the participant is allowed to keep asking. If the answer is "no" the roles of asking and answering person are reversed. In this way, the roles are switched several times until one person correctly guesses the name. If one participant wins a game he or she gets a point. After the entire session (nine games) the participant who won most games wins the entire session and with this an additional prize (a voucher).*
+
+Advantage(s): Let people use both audio and video channel to communicate. In particular, the primarily social interaction in this task facilitates visual communication in terms of nonverbal signals such as smiles (and generally facial expressions), gestures or the change of body posture and gaze.
+
+Disadvantage(s): Works best for participants who know each other. For participants who do not know each other, difficulties in guessing the other's name may lead to frustration, especially when the reactions of the conversation partner cannot be properly interpreted due to the lack of familiarity.
+
+### **A.4 Navigation tasks**
+
+Each subject has a partially complete map of the same area, and take turns to explain to the other participants a route through the map. This will include filling in the incomplete sections of the map. Ideally the subjects will need to exchange and confirm a lot of relatively simple information.
+
+The time taken to complete the task may also be used as an indication of the performance.
+
+Good points: Forces all subjects to get involved.
+
+Poor points: Poor for subjective opinion, since subjects tend to rate the complexity of the task.
+
+### **A.5 Story with missing parts**
+
+In this task the test subjects each get a paper with the same story but with various small sections missing. One participant starts to read the story and the other participants reads the text silently, and interrupts when the reader missed a part of the text. Then the person that noticed that there was a part missing reads that part and continues to read the text until he is interrupted in a similar manner. As the reader continues to read until he hears the other person speak, this conversational task leads to several double talk situations. It is recommended that each conversation lasts between 3 and 5 minutes.
+
+Good points: Extendable to many test subjects.
+
+Poor points: Not suitable for audiovisual tests as the test subjects need to read the stories and are not free to look at their conversation partners.
+
+### **A.6 Building blocks task – variation**
+
+This is an extension of the small building blocks task described in [ITU-T P.920] for small groups. In the [ITU-T P.920] version one participant has an assembled version of a model and the other a disassembled version. The goal is that both participants have an assembled version at the end. To extend this to a multi-party scenario, all participants have a disassembled version of the model. The instruction manual to build the final model is however in parts distributed to the participant. The goal is again that each participant has an assembled version of the model in the end. Also the
+
+[ITU-T P.920] recommendation of a minimum size of  $3\text{ cm} \times 3\text{ cm} \times 2\text{ cm}$  should be adjusted to video quality and resolution of the system under test.
+
+Good points: Requires audiovisual interaction.
+
+Poor points: Does not represent a typical conversation.
+
+### **A.7 Survival task – variations**
+
+This is a task similar to the survival task in [ITU-T P.1301]. Also in this task, the participants are asked to imagine themselves in a dangerous outdoor situation. Contrary to the "rank items"-style of the [ITU-T P.1301] survival task, this task has a quiz style "questions and select answer" interaction. This style makes it easier to use it multiple times with the same participants for a repeated measure design assessment. It shares many properties with the [ITU-T P.1301] survival task: it is a team building exercise in a cooperative consensus seeking task for small groups, thus suitable for participants which are not familiar with each other. It is further also a "knowledge free" task, meaning that it is assumed that participants are not experts in outdoor survival. The task was found to stimulate discussion and was commented as engaging by most participants. In the task a question about a particular outdoor situation is given with three answer options. The correct answer to the question is based on expert opinions and are accompanied with a specific reasoning. Questions and answers can be found under [b-Biech, 2007]. Every participant should answer the questions first alone before the group discussion begins. This is meant to help to assess how well this group of people works as a team: for a working team the participants should achieve at least the amount of points the highest scoring participant had.
+
+Good points: Good for assessing goal oriented ad-hoc group discussions.
+
+Poor points: Participation might be very unequal based on knowledge about the topic.
+
+## Annex B
+
+## Suggestions for delay-critical tasks
+
+(This annex forms an integral part of this Recommendation.)
+
+### B.1 Information exchange tasks
+
+A number of tasks to evaluate the effects of speech delay on communication quality are provided in Appendix I of [ITU-T P.920]. The first 5 of these are simple information exchange tasks and as such very delay sensitive.
+
+- 1) take turns in counting;
+- 2) take turns reading random numbers aloud as quickly as possible;
+- 3) take turns verifying random numbers aloud as quickly as possible;
+- 4) words with missing letters are completed with letters supplied by the other talker;
+- 5) take turns verifying city names as quickly as possible.
+
+### B.2 Random number verification task timed
+
+This task is a modified version of the number verification task, described in Appendix VIII in [ITU-T P.805]. The essential difference is that test participants are explicitly encouraged to solve the task as quickly as possible, for instance by informing them, that the fastest group of participants in the whole experiment will win a price. This modification has been found to increase the sensitivity [b-Schoenenberg, 2014].
+
+An extension to three parties has been developed for the German language as well [b-Schoenenberg, 2014].
+
+Advantage(s): High sensitivity to delay. Triggers fast interaction between participants.
+
+Disadvantage(s): Lack of naturalness of the task. Participants may try short-cuts by violating the rules of taking turns when reading and confirming the numbers. Thus, test supervisors should listen to the conversations and remind participants not to use short-cuts.
+
+# Bibliography
+
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+- [b-Biech, 2007] Biech, E. (2007), *The Pfeiffer book of successful team-building tools: Best of the annuals*. Pfeiffer.
+- [b-Brady, 1965] Brady, P.T. (1965), *A technique for investigating on-off patterns of speech*, Bell Syst. Tech. J., Vol. 44, No. 1, pp. 1-22.
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+- [b-Brady, 1971] Brady, P.T. (1971), *Effects of transmission delay on conversational behavior on echo-free telephone circuits*, Bell Syst. Tech. J., Vol. 50, No. 1, pp. 115-134.
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+- [b-Gisladottir, 2015] Gisladottir, R., Chwillia, D.J., Levinson, S.C. (2015), *Conversation Electrified: ERP Correlates of Speech Act Recognition in Underspecified Utterances*, PLOS ONE | DOI:10.1371/journal.pone.0120068 March 20.
+- [b-Guégain, 2006] Guégain, M., Le Bouquin-Jeannès, R., Faucon, G. and Barriac, V. (2006), *Towards an objective model of the conversational speech quality*, in Int. Conf. on Acoustics, Speech and Signal Processing (ICASP), IEEE.
+- [b-Hammer, 2004] Hammer, Florian, Reichl, Peter, and Raake, Alexander (2004), *Elements of interactivity in telephone conversations*. In: Proceedings of the 8th International Conference on Spoken Language Processing (Interspeech, 2004). Jeju Island, Korea, 2004, pp. 1741-1744.
+- [b-ITU Handbook] *ITU Handbook: Practical procedures for subjective testing* (2011).
+- [b-Jefferson, 1989] Jefferson, G. (1989), *Preliminary notes on a possible metric which provides for a 'standard maximum' silence of approximately one second in conversation*. Conversation: An interdisciplinary perspective. Intercommunication series, 3, (pp. 166-196). Roger, Derek (Ed); Bull, Peter (Ed).
+- [b-Kitawaki, 1991] Kitawaki, N. and K. Itoh, K. (1991), *Pure delay effects on speech quality in telecommunications*, in IEEE Journal on Selected Areas in Communications, Vol. 9, No. 4, pp. 586-593.
+- [b-Knapp, 2010] Knapp, M.L. and Hall, J.A. (2010), *Nonverbal communication in human interaction*, 7th edition, Wadsworth, Cenage Learning, Boston, USA.
+
+- [b-OConnail, 1993] O'Connail, B., Whittaker, S. and Wilbur, J.A. (1993), *Conversations over video conferences: An evaluation of the spoken aspects of video-mediated communication*, Human-Computer Interaction, Vol. 8, pp. 389-428.
+- [b-Raake, 2013] Raake, A., Schoenenberg, K., Skowronek, J. & Egger, S. (2013), *Predicting speech quality based on interactivity and delay*. In: Proc. Interspeech, Lyon, France, August.
+- [b-Sacks,1974] Sacks, H., Schegloff, E.A., Jefferson, G. (1974), *A simplest systematics for the organisation of turn-taking in conversation*. [Journal] // Language 50. pp. 696-735.
+- [b-Schmitt, 2014a] Schmitt, M., Gunkel, S., Cesar, P., and Bulterman, D. (2014), *The influence of interactivity patterns on the Quality of Experience in multi-party video-mediated conversations under symmetric delay conditions* in Proceedings of the 3rd International Workshop on Socially-aware Multimedia, New York, NY, USA.
+- [b-Schmitt, 2014b] Schmitt, M., Gunkel, S., Pablo, C., and Bulterman, D. (2014), *Asymmetric Delay in Video-Mediated Group Discussions* in 6th International Workshop on Quality of Multimedia Experience (QoMEX).
+- [b-Schoenenberg, 2011] Schoenenberg, K., Raake, A. & Skowronek, J. (2011), *A conversation analytic approach to the prediction of leadership in two to six-party audio conferences*. Third International Workshop on Quality of Multimedia Experience (QoMex), pp. 119-124.
+- [b-Schoenenberg, 2014] Schoenenberg, K., Raake, A., Egger, S., & Schatz, R. (2014), *On interaction behaviour in telephone conversations under transmission delay*. Speech Communication, 63-64, pp. 1-14.
+- [b-Schoenenberg, 2014b] Schoenenberg, K., Raake, A., Lebreton, P. (2014), *Conversational Quality and Visual Interaction of Video-Telephony under Synchronous and Asynchronous Transmission Delay*, Sixth International Workshop on Quality of Multimedia Experience (QoMex).
+- [b-Schoenenberg, 2016] Schoenenberg, K. (2016), *The Quality of Mediated-Conversations under Transmission Delay*. PhD thesis, TU Berlin.
+- [b-Tam, 2012] Tam, J., Carter, E., Kiesler, S. and Hodgins, J. (2012), *Video increases the perception of naturalness during remote interactions with latency*, in Proc. of CHI'12, New York, NY, USA, pp. 2045-2050.
+- [b-Tang, 1992] Tang, J.C. (1992), *Why Do Users Like Video? Studies of Multimedia-Supported Collaboration*, Sun Microsystems, Inc., Mountain View, CA, USA.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| <b>Series P</b> | <b>Terminals and subjective and objective assessment methods</b>                                                                                          |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks, Internet of Things and smart cities                            |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/P/T-REC-P.16-198811-I_PDF-E/raw.md

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+
+
+![ITU logo](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with latitude and longitude lines. A lightning bolt symbol is positioned to the right of the globe.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**P.16**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+# **TELEPHONE TRANSMISSION QUALITY**
+
+## **VOCABULARY AND EFFECTS OF TRANSMISSION PARAMETERS ON CUSTOMER OPINION OF TRANSMISSION QUALITY AND THEIR ASSESSMENT** ---
+
+## **SUBJECTIVE EFFECTS OF DIRECT CROSSTALK; THRESHOLDS OF AUDIBILITY AND INTELLIGIBILITY**
+
+**ITU-T Recommendation P.16**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation P.16 was published in Volume V of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+### **SUBJECTIVE EFFECTS OF DIRECT CROSSTALK; THRESHOLDS OF AUDIBILITY AND INTELLIGIBILITY**
+
+*(Geneva, 1972; amended at Geneva, 1976, 1980;  
+Malaga-Torremolinos, 1984; Melbourne, 1988)*
+
+#### **1 Factors which affect the crosstalk threshold**
+
+The degree of audibility and intelligibility of a crosstalk signal depends on a large number of factors.
+
+The main factors influencing the intelligibility of the vocal crosstalk signal are listed below.
+
+##### **1.1 *Quality of transmission of telephone apparatus***
+
+The sending and receiving loudness ratings are decisive factors. The same is true of the sidetone rating when room noise is present. The use of modern telephone apparatus with smooth frequency response curves is assumed.
+
+##### **1.2 *Circuit noise***
+
+The circuit noise on the connection of the disturbed call must be taken into account. The noise level is measured by a psophometer equipped with a weighting network for telephone circuits, as described in Recommendation O.41.
+
+##### **1.3 *Room noise***
+
+Room noise affects the ear directly through earcap leakage between the ear and the receiver and indirectly by sidetone. Sidetone also depends on operating conditions. Unlike circuit noise, the effect of room noise can be reduced to some extent by the user of the telephone. For this reason, and to allow for unfavourable cases, measurements on the audibility of crosstalk have been made with slight room noise as well as with negligible room noise. Because the audibility threshold is very sensitive to masking effects, "negligible" room noise means a noise level well below 10 dBA. The relatively low noise level of 40 dBA has a very marked masking effect and may therefore serve as an example of "slight" room noise.
+
+##### **1.4 *Telephone set noise***
+
+In addition to the masking effects on crosstalk by circuit noise and room noise, the internal noise of the telephone set in the disturbed connection has to be considered. In modern telephone sets this noise is generated in the electronic circuitry (amplifiers, etc.) while in older sets the origin is noise from the carbon microphone. The internal noise can be expressed and treated as an equivalent circuit noise.
+
+##### **1.5 *Conversation on the disturbed connection***
+
+During active speech on the disturbed connection, practical levels of crosstalk are inaudible. However, before the conversation starts or during long pauses in the conversation, it is possible for crosstalk to be heard and perhaps understood. In general, it would be unwise to plan on the basis that the disturbed connection is always active; accordingly, the information given in this Recommendation assumes no conversation on the disturbed connection.
+
+##### **1.6 *Crosstalk coupling***
+
+The intelligibility of a vocal crosstalk signal depends largely on the nature of the crosstalk coupling, which is generally a function of frequency.
+
+The loudness rating of the crosstalk transmission path – from the speech signal present on the disturbing line to the subscriber's set subject to the disturbance – can be divided into the loudness loss of the crosstalk path from the disturbing to the disturbed line and the receive loudness rating of the disturbed subscriber's set. Figure 1/P.16 illustrates this subdivision.
+
+![Diagram illustrating the subdivision of crosstalk transmission path. It shows two parallel horizontal lines representing telephone lines. The top line has a sending terminal 'e' connected to a voice source 'Vc' and a receiving terminal 'r' connected to a Psophometer 'mV'. The bottom line has terminals 'B' at both ends. A dashed curved line labeled 'Crosstalk transmission path' connects terminal 'e' on the top line to terminal 'B' on the bottom line. A solid curved line labeled 'd' (loudness loss) connects terminal 'B' on the bottom line to terminal 'r' on the top line. An arrow labeled 'Direction of the voice signal' points to the right on the top line. The diagram is labeled 'T1202020-88'.](2763901b7a1fd1b5d704cdc450d12ed0_img.jpg)
+
+Diagram illustrating the subdivision of crosstalk transmission path. It shows two parallel horizontal lines representing telephone lines. The top line has a sending terminal 'e' connected to a voice source 'Vc' and a receiving terminal 'r' connected to a Psophometer 'mV'. The bottom line has terminals 'B' at both ends. A dashed curved line labeled 'Crosstalk transmission path' connects terminal 'e' on the top line to terminal 'B' on the bottom line. A solid curved line labeled 'd' (loudness loss) connects terminal 'B' on the bottom line to terminal 'r' on the top line. An arrow labeled 'Direction of the voice signal' points to the right on the top line. The diagram is labeled 'T1202020-88'.
+
+- e sending LR of the disturbing subscriber's set
+- r receiving LR of the disturbed subscriber's set
+- d crosstalk path loudness loss
+- B terminals of subscriber's set
+- $V_c$  conversational speech level
+
+Disturbing and disturbed subscriber's sets at the same end: near-end crosstalk.
+
+Disturbing and disturbed subscriber's sets at opposite ends: far-end crosstalk.
+
+FIGURE 1/P.16
+
+#### Subdivision of crosstalk transmission path
+
+For a given speech level  $V_c$ , the intelligibility of the crosstalk signal depends on the loudness rating  $d + r$ . In Recommendation G.111, § A.4.4.4, the crosstalk receive loudness rating is defined as:
+
+$$XRLR = RLR(set) + L_x$$
+
+where  $RLR(set)$  refers to the disturbed telephone set.
+
+The crosstalk loudness  $L_x$  is computed as a loudness rating but with the exponent  $m = 1$ , which is valid near the audibility threshold.
+
+In the absence of further information, the value of  $L_x$  may be approximately taken as the attenuation measured or calculated at a frequency of 1020 Hz.
+
+#### 2 Median listener threshold of the audibility and intelligibility of vocal crosstalk
+
+The curves in Figure 2/P.16 represent the crosstalk receive loudness rating corresponding to the threshold of audibility and intelligibility ( $XRLR_t$ ) as a function of circuit noise. For planning purposes, it is recommended that room noise be regarded as negligible, which represents the most unfavourable condition.
+
+![Figure 2/P.16: Threshold value of crosstalk receive loudness rating as a function of circuit noise. The graph shows two curves on a grid. The y-axis is 'Crosstalk receive loudness rating (XRLR_t) dB' from 40 to 80. The x-axis is 'Circuit noise dBmp' from -90 to -50. The top curve is labeled 'Audibility threshold' and the bottom curve is labeled 'Intelligibility threshold'. Both curves decrease as circuit noise increases. A label '(Without sidetone)' is at the top. A small code 'T1202030-88' is at the bottom right.](de6e8b740c69dac308cce9edfec3eff4_img.jpg)
+
+| Circuit noise (dBmp) | Audibility threshold (XRLR <sub>t</sub> dB) | Intelligibility threshold (XRLR <sub>t</sub> dB) |
+|----------------------|---------------------------------------------|--------------------------------------------------|
+| -90                  | 80                                          | 67                                               |
+| -80                  | 75                                          | 62                                               |
+| -70                  | 68                                          | 55                                               |
+| -60                  | 60                                          | 48                                               |
+| -50                  | 50                                          | 40                                               |
+
+Figure 2/P.16: Threshold value of crosstalk receive loudness rating as a function of circuit noise. The graph shows two curves on a grid. The y-axis is 'Crosstalk receive loudness rating (XRLR\_t) dB' from 40 to 80. The x-axis is 'Circuit noise dBmp' from -90 to -50. The top curve is labeled 'Audibility threshold' and the bottom curve is labeled 'Intelligibility threshold'. Both curves decrease as circuit noise increases. A label '(Without sidetone)' is at the top. A small code 'T1202030-88' is at the bottom right.
+
+*Note 1* – The circuit noise is referred to the terminals of the subscriber's set. Room noise is assumed to be negligible.
+
+*Note 2* – The vocal level on the disturbing line is assumed to be  $-18$  dBV active speech level.
+
+FIGURE 2/P.16
+
+Threshold value of crosstalk receive loudness rating as a function of circuit noise
+
+The criterion for the threshold of audibility is that the presence of a speech signal is only just detectable but that no part of the speech can be understood. The criterion for the threshold of intelligibility is that single words or phrases can sometimes be understood while listening to a conversation.
+
+The threshold curves represent median values for the two criteria such that in each case 50% of subscriber's opinions are respectively above and below the particular curve. The standard deviation for listeners has been observed to lie in the range 4 to 6 dB and a value of 5 dB is recommended for planning purposes. Typical response curves for a large sample of listeners for the threshold criteria are shown in Figure 3/P.16 (no circuit noise). The difference in XRLR between the two curves is about 12 dB.
+
+The results of the original experiments (from which the curves in Figure 2/P.16 were drawn) were expressed in terms of speech level (e.g. in Volume Units (VU)) and on that basis showed a satisfactory degree of coherence.
+
+However, earlier versions of Recommendation P.16 were based on the assumption that there is a fixed relationship between the sending loudness rating and the speech level on the line. This assumption required a correction in the range of 11 dB and is therefore not justified. Furthermore, speech levels expressed in Volume Units appear to differ systematically as measured in different countries on identical speech samples. Therefore, a fixed speech level on the disturbing line is assumed, independent of the send loudness rating (SLR) of that circuit.
+
+The thresholds given in Figure 2/P.16 are based on the assumption that the speech level  $V_c$  under normal conversational conditions is  $-18$  dBV active speech level (measured according to Recommendation P.56) at the terminal of the disturbing telephone set. This value is the estimated average of the conversational level in many countries at the send end of a connection with fairly high overall loudness rating [between the optimum and the maximum permitted (OLR)].
+
+![Figure 3/P.16: A graph showing the probability (0 to 100%) versus Crosstalk receive loudness rating (XRLR) in dB (50 to 100). Two curves are plotted: 'Audibility' and 'Intelligibility'. The 'Audibility' curve starts at 100% probability at 50 dB and decreases to 0% at approximately 95 dB. The 'Intelligibility' curve starts at 100% probability at 50 dB and decreases to 0% at approximately 85 dB. The graph is labeled 'TI202040-88' in the bottom right corner.](431b8889a0e7f676f0eef40859590349_img.jpg)
+
+| Crosstalk receive loudness rating (XRLR) [dB] | Audibility Probability [%] | Intelligibility Probability [%] |
+|-----------------------------------------------|----------------------------|---------------------------------|
+| 50                                            | 100                        | 100                             |
+| 60                                            | 95                         | 85                              |
+| 70                                            | 85                         | 40                              |
+| 80                                            | 50                         | 5                               |
+| 90                                            | 10                         | 0                               |
+| 100                                           | 0                          | 0                               |
+
+Figure 3/P.16: A graph showing the probability (0 to 100%) versus Crosstalk receive loudness rating (XRLR) in dB (50 to 100). Two curves are plotted: 'Audibility' and 'Intelligibility'. The 'Audibility' curve starts at 100% probability at 50 dB and decreases to 0% at approximately 95 dB. The 'Intelligibility' curve starts at 100% probability at 50 dB and decreases to 0% at approximately 85 dB. The graph is labeled 'TI202040-88' in the bottom right corner.
+
+FIGURE 3/P.16  
+Listener distribution of crosstalk receive loudness rating  
+required for different threshold definitions
+
+The standard deviation of talking levels is fairly high. For calculation purposes a value of  $\sigma = 5$  dB should be used.
+
+To calculate the threshold value for a speech level different from  $-18$  dBV, the  $XRLR_t$  value should be corrected by the amount of the difference, with its sigh (higher levels require higher  $XRLR$  values, and vice versa).
+
+The value  $XRLR_t$  is the sum of the crosstalk path loudness loss and the receiving loudness loss on the disturbed line. In order to obtain the loudness loss of the crosstalk path,  $L_x$ , for a particular threshold value, the  $RLR(set)$  value has to be subtracted.
+
+In general, for any speech level and receiving loudness rating,  $L_x$  is obtained from Figure 2/P.16 as:
+
+$$L_x = XRLR_t - RLR(set) + (18 + V_c)$$
+
+#### 3 Effects of room noise
+
+Room noise reaches the listener's ear both by leakage under the earcap of the telephone handset and by the sidetone path. For a given sidetone the room noise can be converted to an equivalent circuit noise by means of a transmission model such as described in Supplement No. 3. A family of conversion curves with sidetone loss as parameter is found in Figure 2 of this Supplement.
+
+As an example, with a fairly high sidetone loss (the same as used in the previous version of Recommendation P.16) a level of 40 dBA room noise is equivalent to a circuit noise level of  $-85$  dBmp. This noise level reduces the threshold  $XRLR$  value by about 8 dB. An additional reduction will in most cases be caused by earcap leakage.
+
+However, the importance of this effect cannot be generally predicted, since it depends both on the shape of the earcap and on user habits.
+
+#### 4 Crosstalk probability
+
+While the curves in Figure 2/P.16 present the median values for various noise conditions, the curves in Figure 3/P.16 represent the probability of audible or intelligible crosstalk, in percent, for the negligible noise condition. Similar probability curves can be derived from the median values for any circuit noise condition by the use of cumulative normal distributions with a standard deviation of 6 dB.
+
+In a more general case, the talker variance should also be added. The mean speech level used in the calculations may be chosen to be lower than the relatively high level assumed in Figure 2/P.16, e.g.  $-20$  dBV, which is closer to the average level in the network. An example of such an overall probability calculation is given in Annex A.
+
+The threshold values of crosstalk loudness rating given in this Recommendation can be used in different ways. One possible interpretation is to require all normal telephone connections (i.e. faulty connections excluded) to have crosstalk conditions between the two threshold criteria. This means that, on the one hand, there is no point in requiring a higher crosstalk attenuation than the one corresponding to the audibility threshold and, on the other hand, that the intelligibility threshold should not be exceeded.
+
+Another interpretation is to set the requirement so that there is a given small probability (e.g. 5%) that intelligible crosstalk can be encountered with negligible room noise and with the lowest circuit noise level found in the network. In practice, noise conditions are more favourable in the sense that crosstalk quite often is masked by room and circuit noise to the extent of becoming inaudible. For the average of all connections the risk of intelligible crosstalk will therefore be much smaller than the given percentage for the most unfavourable condition.
+
+Crosstalk requirements may not necessarily be the same for all parts of the network. Although the maintenance of telephone secrecy is primordial, the subscriber is more likely to make a severe judgement on crosstalk in a local call taking place in his immediate environment and in which indiscretion due to crosstalk may have unfortunate social consequences. The problem of "social crosstalk" is dealt with in [1].
+
+In practice, simultaneity of speaking on the disturbing line and listening on the disturbed line (during conversation pauses) is not present in all cases. Information concerning this topic and showing how to calculate the probabilities concerned will be found in [2].
+
+As guidelines, the probabilities of subscribers encountering potentially intelligible crosstalk should not be worse (i.e. higher) than the following:
+
+- own exchange calls: 1 in 1000,
+- other calls: 1 in 100.
+
+*Note* – The fundamentals of calculating crosstalk probability in general are considered in Recommendation G.105.
+
+## ANNEX A
+
+(to Recommendation P.16)
+
+### Example of probability calculation
+
+The probability of understanding single words of a conversation overheard by crosstalk may be calculated for a listener chosen at random from a population of subscribers. The result of such a calculation can be used as a basis for establishing rules for, inter alia, the minimum required crosstalk attenuation between subscriber lines in a national network.
+
+In order to demonstrate the method of using the information given in this Recommendation to calculate the probability of encountering (intelligible) crosstalk, the following assumptions may be made:
+
+Mean speech level  $V_c = -20$  dBV;
+
+Receive loudness rating of telephone sets  $RLR(set) = -6$  dB;
+
+No room or circuit noise;
+
+Standard deviation of talking levels  $\sigma_T = 5$  dB;
+
+Standard deviation of listener response distribution  $\sigma_L = 6$  dB;
+
+Standard deviation of  $RLR(set)$   $\sigma_s = 1$  dB.
+
+The threshold value for crosstalk intelligibility without noise, taken from Figure 2/P.16 is  $XRLR_t = 67$  dB.
+
+According to the formula at the end of § 2 and with the given assumptions, the required median crosstalk path loudness loss becomes:
+
+$$L_x = 67 + 6 - 2 = 71 \text{ dB.}$$
+
+The total standard deviation of the probability function is:
+
+$$\sqrt{\sigma_T^2 + \sigma_L^2 + \sigma_s^2} = 7.87 \text{ dB}$$
+
+With these values of  $L_x$  and  $\sigma$ , a cumulative normal distribution function as in Figure A-1/P.16 can be drawn. The function indicates the probability that a listener can understand single words if crosstalk for a specific value of the crosstalk path loudness loss. For example, for  $L_x = 75$  the probability is 30%. On the other hand, to obtain only 5% probability a crosstalk path loudness loss of 84 dB would be necessary. For 1% probability, 89 dB would be required, as well as 95 dB for 0.1% probability.
+
+This calculation was based on some typical values of speech level and receiving sensitivity under noise-free conditions. Similar calculations can easily be made with other data, also including the effects of noise. For a realistic estimation of the probability of intelligible crosstalk for subscribers in general, some statistical distribution of circuit noise (and possibly of room noise at the subscriber's locations) will have to be assumed.
+
+![Figure A-1/P.16: A graph showing the probability of understanding single words of an overheard conversation as a function of the (weighted) crosstalk path loudness loss L_x. The y-axis is labeled 'Probability' and uses a percentage scale from 0.01 to 99.9. The x-axis is labeled 'Crosstalk path loudness loss (L_x)' and ranges from 50 to 100 dB. A straight line is plotted on the graph, indicating a normal distribution. The line passes through approximately (50, 99.9), (60, 95), (70, 50), (80, 10), (90, 1), and (100, 0.01).](643d86ebba41e16a88461bfcb3741de6_img.jpg)
+
+Figure A-1/P.16: A graph showing the probability of understanding single words of an overheard conversation as a function of the (weighted) crosstalk path loudness loss L\_x. The y-axis is labeled 'Probability' and uses a percentage scale from 0.01 to 99.9. The x-axis is labeled 'Crosstalk path loudness loss (L\_x)' and ranges from 50 to 100 dB. A straight line is plotted on the graph, indicating a normal distribution. The line passes through approximately (50, 99.9), (60, 95), (70, 50), (80, 10), (90, 1), and (100, 0.01).
+
+$V_c$  mean =  $-20$  dBV;  $RLR(set) = -6$  dB; standard deviation =  $7.9$  dB
+
+FIGURE A-1/P.16
+
+Probability of understanding single words of an overheard conversation as a function of the (weighted) crosstalk path loudness loss  $L_x$
+
+## References
+
+- [1] WILLIAMS (H.), SILOCOCK (W. W.), SIBBALD (D.): Social crosstalk in the local area network, *El. Comm.*, Vol. 49, No. 4, London, 1974.
+- [2] LAPSA (P. M.): Calculation of multidisturber crosstalk probabilities, *BSTJ*, Vol. 55, No. 7, New York, 1976.

marked/P/T-REC-P.300-200111-I_PDF-E/raw.md

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+
+
+![ITU logo: A globe with a lightning bolt and the letters ITU.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: A globe with a lightning bolt and the letters ITU.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.300**
+
+(11/2001)
+
+SERIES P: TELEPHONE TRANSMISSION QUALITY,  
+TELEPHONE INSTALLATIONS, LOCAL LINE  
+NETWORKS
+
+Subscribers' lines and sets
+
+---
+
+**Transmission performance of group audio  
+terminals (GATs)**
+
+ITU-T Recommendation P.300
+
+---
+
+# ITU-T P-SERIES RECOMMENDATIONS
+
+## TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS
+
+|                                                                                               |               |              |
+|-----------------------------------------------------------------------------------------------|---------------|--------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality | Series        | P.10         |
+| <b>Subscribers' lines and sets</b>                                                            | <b>Series</b> | <b>P.30</b>  |
+|                                                                                               |               | <b>P.300</b> |
+| Transmission standards                                                                        | Series        | P.40         |
+| Objective measuring apparatus                                                                 | Series        | P.50         |
+|                                                                                               |               | P.500        |
+| Objective electro-acoustical measurements                                                     | Series        | P.60         |
+| Measurements related to speech loudness                                                       | Series        | P.70         |
+| Methods for objective and subjective assessment of quality                                    | Series        | P.80         |
+|                                                                                               |               | P.800        |
+| Audiovisual quality in multimedia services                                                    | Series        | P.900        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# **Transmission performance of group audio terminals (GATs)**
+
+## **Summary**
+
+This Recommendation provides the speech transmission requirements for Group Audio Terminals (GATs). The associated test methods for verifying the specified performances are contained in Annex A. An *in-situ* procedure for checking and aligning GAT terminals in the field is provided in Appendix I.
+
+Reference is made, as far as possible, to other Recommendations applicable to speech terminals for analogue and digital networks. Only terminal configurations not already covered by these Recommendations are addressed in detail.
+
+## **Source**
+
+ITU-T Recommendation P.300 is a revision of ITU-T Rec. P.30 (1998). It was revised by ITU-T Study Group 12 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 November 2001.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
+
+© ITU 2002
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU.
+
+## CONTENTS
+
+###### Page
+
+|       |                                                                                                         |    |
+|-------|---------------------------------------------------------------------------------------------------------|----|
+| 1     | Scope.....                                                                                              | 1  |
+| 2     | Normative references .....                                                                              | 1  |
+| 3     | Definitions and abbreviations .....                                                                     | 2  |
+| 4     | Group Audio Terminals types.....                                                                        | 2  |
+| 5     | Speech transmission characteristics.....                                                                | 3  |
+| 5.1   | Handset mode .....                                                                                      | 3  |
+| 5.2   | Headset mode.....                                                                                       | 3  |
+| 5.3   | Hands-free mode (single-user facilities).....                                                           | 3  |
+| 5.4   | Hands-free mode (multiple-users facility).....                                                          | 3  |
+| 5.4.1 | Receiving volume control and sensitivity adjustments .....                                              | 4  |
+| 5.4.2 | Sensitivity-frequency responses .....                                                                   | 4  |
+| 5.4.3 | Loudness Rating .....                                                                                   | 4  |
+| 5.4.4 | Echo path loss characteristics .....                                                                    | 5  |
+| 5.4.5 | Distortion .....                                                                                        | 5  |
+| 5.4.6 | Out-of-band requirements.....                                                                           | 5  |
+| 5.4.7 | Noise .....                                                                                             | 5  |
+| 5.4.8 | Delay.....                                                                                              | 5  |
+|       | Annex A – Objective measurement methods for hands-free, multiple users GATs .....                       | 6  |
+| A.1   | Introduction.....                                                                                       | 6  |
+| A.1.1 | Testing arrangements.....                                                                               | 6  |
+| A.1.2 | Test signals levels .....                                                                               | 7  |
+| A.2   | Testing of transmission requirements .....                                                              | 8  |
+| A.2.1 | Sensitivity-frequency response.....                                                                     | 8  |
+| A.2.2 | Loudness rating.....                                                                                    | 9  |
+| A.2.3 | Terminal Coupling Loss .....                                                                            | 9  |
+|       | Appendix I – Practical <i>in-situ</i> audio alignment procedure for multiple-users hands-free GATs..... | 10 |
+| I.1   | Introduction.....                                                                                       | 10 |
+| I.2   | Audio alignment and sensitivity-frequency characteristics .....                                         | 10 |
+| I.2.1 | Sending .....                                                                                           | 11 |
+| I.2.2 | Receiving .....                                                                                         | 11 |
+
+
+
+# **Transmission performance of group audio terminals (GATs)**
+
+# **1 Scope**
+
+This Recommendation provides the audio performance requirements and test methods for Group Audio Terminals (GATs), i.e. terminals which are specifically designed for being used by several users at the same time.
+
+GATs cover a wide range of products, ranging from the hands-free telephone set, when used by several users at the same time, to the teleconference audio terminals incorporating sophisticated echo control mechanisms. GATs can be designed to operate both on the analog POTS networks and on digital ISDN links. While the former can only offer telephone bandwidth performances, the latter can be designed to offer either narrow-band or wideband audio communication facilities.
+
+This Recommendation addresses this whole range of devices by identifying, as far as possible, the already existing Recommendations applicable to each terminal type.
+
+# **2 Normative references**
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision: all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published.
+
+- [1] ITU-T Recommendation P.310 (2000), *Transmission characteristics for telephone-band (300-3400 Hz) digital telephones.*
+- [2] ITU-T Recommendation P.311 (1998), *Transmission characteristics for wideband (150-7000 Hz) digital handset telephones.*
+- [3] ITU-T Recommendation P.57 (1996), *Artificial ears.*
+- [4] ITU-T Recommendation P.10 (1998), *Vocabulary of terms on telephone transmission quality and telephone sets.*
+- [5] ITU-T Recommendation P.340 (2000), *Transmission characteristics and speech quality parameters of hands-free telephones.*
+- [6] ITU-T Recommendation P.342 (2000), *Transmission characteristics for telephone band (300-3400 Hz) digital loudspeaking and hands-free telephony terminals.*
+- [7] ITU-T Recommendation P.341 (1998), *Transmission characteristics for wideband (150-7000 Hz) digital hands-free telephony terminals.*
+- [8] ITU-T P-Series Recommendations – Supplement 16 (1988), *Guidelines for placement of microphones and loudspeakers in telephone conference rooms [1] and for Group Audio Terminals (GATs).*
+- [9] ITU-T Recommendation P.51 (1996), *Artificial mouth.*
+- [10] ITU-T Recommendation P.79 (1999), *Calculation of loudness ratings for telephone sets.*
+- [11] ISO 3:1973, *Preferred numbers – Series of preferred numbers.*
+
+- [12] ITU-T Recommendation G.122 (1993), *Influence of national systems on stability and talker echo in international connections*.
+- [13] IEC 60651 (2001), *Sound level meters*.
+- [14] ITU-T Recommendation P.50 (1999), *Artificial voices*.
+
+# 3 Definitions and abbreviations
+
+Relevant definitions and abbreviations in ITU-T Rec. P.10 [4] apply.
+
+For the purposes of this Recommendation, the following terms are additionally defined:
+
+**3.1 Group Audio Terminal (GAT):** Terminal designed for being used by several users at the same time and specifically intended for accessing point-to-point and multipoint teleconference sessions.
+
+**3.2 reference codec:** Practical implementation of an ideal codec. Used for carrying out speech transmission measurements on digital terminal equipment by means of analogue instrumentation. The Reference Codec shall provide a 0 dBr analogue interface to the testing instrumentation and implement the relevant coding algorithms (e.g. ITU-T Rec. G.711 for telephone band measurements and ITU-T Rec. G.722 for wide band applications).
+
+**3.3 reference sphere:** One meter radius sphere inside an echo-free environment, where anechoic conditions exist within the tolerance limits specified in ITU-T Rec. P.341 [7] (Table A.1/P.341). Three orthogonal axes are defined through the center of the Reference Sphere: x and y (horizontal) and z (vertical).
+
+The following abbreviations are used:
+
+- $d_r$  Loudspeaker-listener nominal operating distance of hands-free multiple users GATs
+- $d_s$  Microphone-speaker operating distance of hands-free multiple users GATs
+- $F_r$  Correction factor for receiving hands-free measurements of hands-free multiple users GATs
+- $F_s$  Correction factor for sending hands-free measurements of hands-free multiple users GATs
+- $F_{tcl}$  Correction factor for terminal coupling loss measurements of hands-free multiple users GATs
+- ISDN Integrated Services Digital Network
+- POTS Plain Old Telephone Service
+- RLR Receiving Loudness Rating
+- SLR Sending Loudness Rating
+
+# 4 Group Audio Terminals types
+
+The GAT terminals are intended for supporting communications between groups of users, either point-to-point or multipoint.
+
+The following types of audio facilities can be provided by GAT terminals, either separately or in combination:
+
+- handsets;
+- headsets;
+- hands-free (single-user facilities);
+- hands-free (multiple-users facility).
+
+GATs can be designed to provide telephone-band and/or wideband audio facilities.
+
+# 5 Speech transmission characteristics
+
+The GAT terminals shall be able to interwork (end-to-end) with analogue (POTS) and digital (ISDN) narrow-band telephone sets, as well as with ISDN videophones and wideband telephones. As a consequence, the audio standards applicable to these devices also apply to GAT terminals intended for the same network access, as appropriate and as specified below.
+
+## 5.1 Handset mode
+
+For GATs designed for interconnecting with the analogue network access, the same relevant regional requirements applicable to POTS telephone sets are also applicable.
+
+For GATs designed for interconnecting with the ISDN network access, the requirements and measurement methods of ITU-T Recs. P.310 [1] and P.311 [2] apply, respectively for telephone-band and wideband operations.
+
+## 5.2 Headset mode
+
+In principle, the requirements for headset operations shall be based on the requirements for handset operations, with the following allowances:
+
+- the suitable positioning of the microphone with respect to the Mouth Reference Point (MRP) position shall be stated by the manufacturer;
+- an appropriate Artificial Ear shall be used and the measurement results shall be referred to the Ear Reference Point (ERP) position as specified in ITU-T Rec. P.57 [3].
+
+## 5.3 Hands-free mode (single-user facilities)
+
+The following Recommendations apply to GATs terminals designed for providing hands-free facilities to multiple users by combining more single-user facilities.
+
+ITU-T Rec. P.340 [5] applies to GATs designed for the analogue network access.
+
+The requirements and measurement methods of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wide band (ITU-T Rec. G.722) speech coding.
+
+## 5.4 Hands-free mode (multiple-users facility)
+
+Multiple users GAT terminals are typically designed for guaranteeing optimum hands-free audio performance when installed in "typical" conference rooms (i.e. in "live" environments with acoustic reverberation phenomena and background noise). To this purpose, suitable signal processing techniques are frequently used for eliminating the reverberation effects in the transduced signals and/or suppressing the room noise. Performance under real operating conditions can then only be evaluated in the actual installation environments, whose characteristics can not be specified in a general way.
+
+This Recommendation is not then intended to address all the installation conditions of GAT terminals, but specifies their audio performances under reference echo-free conditions. In case this testing environment is not compatible with the technical characteristics of specific terminals, their manufacturers are given the option to state alternative, more suitable, acoustic testing environments for carrying out their characterisation.
+
+An *in-situ* testing procedure for checking the correct audio alignment of installed terminals is provided in Appendix I.
+
+Guidelines for the placement of microphones and loudspeakers in conference rooms can be found in Supplement 16 of the P-series Recommendations [8].
+
+### **5.4.1 Receiving volume control and sensitivity adjustments**
+
+Due to the wide range of operating conditions, both the sending and receiving sensitivity of multiple-user handsfree terminals are generally adjusted at their installation on the basis of the room characteristics and of the distance between the transducers and the users. These adjustment controls shall not be accessible to normal users. An additional user-accessible receiving volume control (referred to in the following as "receiving volume control") can be provided in order to allow the user to establish the optimum listening conditions on the basis of the actual room noise, the number of participants and of other variable factors.
+
+#### **5.4.1.1 Sending sensitivity adjustment**
+
+The sending sensitivity adjustment is intended to allow for varying the positioning of the microphone(s) with respect to the user(s), according to the installation environment constraints. The manufacturer shall state the regulation range of this control and the microphone-to-speaker nominal operating distance ( $d_s$ ) for which the terminal submitted to the tests has been adjusted.
+
+#### **5.4.1.2 Receiving sensitivity adjustment**
+
+The receiving sensitivity adjustment is intended to allow for varying the positioning of the loudspeaker(s) with respect to the user(s) according to the installation environment constraints. The manufacturer shall state the regulation range of this control and the loudspeaker-to-listener nominal operating distance ( $d_r$ ) for which the terminal submitted to the tests has been regulated.
+
+#### **5.4.1.3 Receiving volume control**
+
+Unless stated otherwise, the compliance requirements here provided refer to the maximum position (maximum sensitivity) of the receiving volume control (when manually adjustable).
+
+The dynamic range of the receiving volume control (when manually adjustable) shall be of at least 15 dB.
+
+#### **5.4.1.4 Adaptive gain control**
+
+An adaptive gain control, sensible to the background noise level, may be implemented into the GAT. Its action should result into complementary and symmetrical gain variations, in the receiving and in the sending paths, as a function of the ambient noise level.
+
+### **5.4.2 Sensitivity-frequency responses**
+
+ITU-T Rec. P.340 [5] applies to GATs designed for the analogue network access.
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec.G.711) or wideband (ITU-T Rec. G.722) speech coding.
+
+### **5.4.3 Loudness Rating**
+
+ITU-T Rec. P.340 [5] applies to GATs designed for the analogue network access.
+
+For GATs intended for connection to the ISDN the following applies.
+
+#### **5.4.3.1 Sending**
+
+The nominal value of Sending Loudness Rating (SLR) shall be:
+
+$$\text{SLR} = (+13 - F_s) \text{ dB}$$
+
+where  $F_s$  is as defined in A.1.1.1.
+
+#### **5.4.3.2 Receiving**
+
+The nominal value of Receiving Loudness Rating (RLR) shall be:
+
+$$\text{RLR} = (+ 2 - F_r) \text{ dB}$$
+
+for GATs implementing telephone-band (ITU-T Rec. G.711) speech coding and:
+
+$$\text{RLR} = (+ 5 - F_r) \text{ dB}$$
+
+for GATs implementing wide band (ITU-T Rec. G.722) speech coding.
+
+In the above formulae  $F_r$  is as defined in A.1.1.2.
+
+The volume control range should span the value of the receiving loudness rating equal to that of the corresponding handset telephone, as well as an RLR value about 10 dB lower.
+
+### **5.4.4 Echo path loss characteristics**
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for the telephone band and wideband operations of GATs intended for connection to the ISDN.
+
+### **5.4.5 Distortion**
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding.
+
+### **5.4.6 Out-of-band requirements**
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding.
+
+### **5.4.7 Noise**
+
+#### **5.4.7.1 Sending**
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding.
+
+#### **5.4.7.2 Receiving**
+
+Irrespectively from the speech coding implemented, the A-weighted noise produced in the receiving direction at the measurement point by GATs intended for connection to the ISDN shall not exceed  $-49 \text{ dBPa(A)} + F_r$ .
+
+### **5.4.8 Delay**
+
+The requirements of ITU-T Recs. P.342 [6] and P.341 [7] respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding.
+
+# ANNEX A
+
+## Objective measurement methods for hands-free, multiple users GATs
+
+## A.1 Introduction
+
+This annex describes methods which may be used to measure the speech transmission performances of hands-free, multiple users, Group Audio Terminals intended for ISDN connection.
+
+Unless stated otherwise, the same test conditions apply as specified in applicable ITU-T Recs. as appropriate (i.e. ITU-T Recs. P.342 [6] and P.341 [7] respectively for GATs implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding).
+
+### A.1.1 Testing arrangements
+
+The acoustic reference conditions for measurement purposes are free-field within the Reference Sphere. However, for specific designs, it is up to the manufacturer to specify an alternative (reverberant) testing environment. In this case, the specified measurement conditions shall be stated in the test report.
+
+#### A.1.1.1 Sending
+
+Two different testing conditions shall be used, according to the type of microphone(s) equipping the GAT terminal:
+
+- microphones placed on the table surface in front of one or more speakers;
+- microphone(s) placed elsewhere in the room.
+
+##### Microphones intended for being placed on the table
+
+- The arrangement specified in Figure A.1, placing each microphone in turn at point B. The other microphones shall be removed from the acoustic field of the Artificial Mouth.
+
+##### Microphones intended for being placed elsewhere in the room
+
+- The acoustic pick-up port of the microphone shall be placed at the centre of the Reference Sphere in an anechoic environment and the Artificial Mouth shall be placed with the lip plane tangential to the Sphere. The reference axis of the Mouth shall coincide with the x-axis of the Sphere, while the microphone shall be oriented as specified by the manufacturer. In case of microphones intended to pick up the sounds coming from multiple directions (either omni-directional or steered devices), the extreme incidence angles on the horizontal plane as stated by the manufacturer shall be tested, as well as an intermediate incidence direction. The testing angles actually used for measurements shall be stated in the test report.
+
+In order to take into account the difference between the reference test positioning and the actual microphone-speaker operating distance ( $d_s$ ), for which the terminal is adjusted, the following correction factor  $F_s$  is defined:
+
+$$F_s \text{ dB} = 20 \text{ Log } \frac{d_s}{0.5} \quad (d_s \text{ in meters})$$
+
+For sending noise measurements the sound source shall be muted and all microphones shall be placed in the testing environment.
+
+NOTE – The specified methodology is not applicable for testing hands-free terminals equipped with lapel-mounted (lavalier) microphones, the testing method for which is not yet defined.
+
+![Diagram of the measurement set-up for table placed microphones. It shows a side view of a microphone on a horizontal surface. A dashed vertical line from the microphone to a point 'C' is labeled '30 cm'. A dashed horizontal line from the microphone to the base of the vertical line is labeled '40 cm'. A dashed hypotenuse line from point 'C' to the microphone is labeled '50 cm'. Above point 'C' is a 'Lip ring' and a dashed line labeled 'C' pointing to the lip ring.](0f2a1e4a7b12fe5b8749882ecd636f5c_img.jpg)
+
+T1213030-02
+
+Diagram of the measurement set-up for table placed microphones. It shows a side view of a microphone on a horizontal surface. A dashed vertical line from the microphone to a point 'C' is labeled '30 cm'. A dashed horizontal line from the microphone to the base of the vertical line is labeled '40 cm'. A dashed hypotenuse line from point 'C' to the microphone is labeled '50 cm'. Above point 'C' is a 'Lip ring' and a dashed line labeled 'C' pointing to the lip ring.
+
+**Figure A.1/P.300 – Measurement set-up for table placed microphones**
+
+#### A.1.1.2 Receiving
+
+Each loudspeaker shall be placed in turn at the centre of the Reference Sphere, with its main axis coincident with the x-axis and its outer surface containing the z-axis. The measurement microphone shall be placed on the x-axis, its acoustic centre being at the intersection with the Reference Sphere.
+
+In order to take into account the difference between the reference test positioning and the actual loudspeaker-listener operating distance ( $d_r$ ) for which the terminal is adjusted, the following correction factor  $F_r$  is defined:
+
+$$F_r \text{ dB} = 20 \text{ Log } \frac{d_r}{0.5} \quad (d_r \text{ in metres})$$
+
+#### A.1.1.3 Terminal coupling loss (TCL)
+
+For TCL and stability measurements the more efficient loudspeaker shall be placed at the centre of the Reference Sphere, with its main axis coincident with the x-axis and its outer surface containing the z-axis. The more efficient microphone shall be placed on the x-axis, its acoustic pick-up port being at the intersection with the Reference Sphere and its maximum efficiency pick-up direction parallel to the x-axis. For surface effect microphones, a suitable horizontal positioning plane shall be used with a minimum surface still guaranteeing the proper operation of the microphone. In any case, the positioning surface shall not enter the reference sphere by more than 100 mm.
+
+In order to take into account the difference between the reference test positioning and the actual loudspeaker-to-microphone operating distance for which the terminal is adjusted, the following correction factor  $F_{tcl}$  is defined:
+
+$$F_{tcl} \text{ dB} = 20 \text{ Log } \frac{d_{min}}{0.5}$$
+
+$d_{min}$  (in metres) is the minimum loudspeaker-to-microphone distance specified by the manufacturer. If no specification is provided, a default  $d_{min} = 2 \text{ m}$  value shall be assumed and stated in the test report.
+
+### A.1.2 Test signals levels
+
+#### A.1.2.1 Sending
+
+The test signal level shall be  $(-28.7 - F_s) \text{ dBPa}$  at the Hands-Free Reference Point (HFRP). The characteristics of the Artificial Mouth shall be according to ITU-T Rec. P.51 [9]. Two different methods can be alternatively used for calibrating the Artificial Mouth.
+
+##### **Method 1:** at the HFRP
+
+The input signal from the Artificial Mouth is equalized under free field conditions at the HFRP, such that the spectrum is as specified in A.1 and the total level in the frequency range corresponding to the third octave bands from 100 Hz to 8 kHz is  $(-28.7 - F_s)$  dBPa. For calculating SLR and response characteristics the reference point is MRP. The sound pressure level at the MRP shall be calculated (by definition) by adding 24 dB to the sound pressure level at the HFRP.
+
+##### **Method 2:** at the MRP
+
+The signal generated by the Artificial Mouth is equalized at the MRP under free field conditions to obtain the spectrum specified in A.1, at a level of  $-4.7$  dBPa in the frequency range corresponding to the third octave bands from 100 Hz to 8 kHz. The spectrum at the MRP is then recorded and the level is adjusted to obtain  $(-28.7 - F_s)$  dBPa at the HFRP. The spectrum recorded at the MRP is used as a reference for calculating SLR and response characteristics.
+
+## **A.2 Testing of transmission requirements**
+
+### **A.2.1 Sensitivity-frequency response**
+
+#### **A.2.1.1 Sending**
+
+The measurement shall be carried out for each microphone, which shall be mounted as specified in A.1.1.1. In case of microphones intended to pick up the sounds coming from multiple directions (either omni-directional or steered devices), the extreme incidence angles on the horizontal plane (as stated by the manufacturer) shall be tested, as well as an intermediate incidence direction. If stated by the manufacturer, the nominal direction shall be used as intermediate. The testing angles actually used for measurements shall be stated in the test report.
+
+The noise signal shall be generated by the Artificial Mouth at the level specified in A.1.2.1.
+
+The spectrum of the output signal shall be measured at the output interface of the reference codec.
+
+The sending sensitivity shall be calculated as follows, according to the calibration method used (see A.1.2.1):
+
+##### **Method 1**
+
+The sending sensitivity is given by the difference between the electric spectrum and the acoustic spectrum at the MRP:
+
+$$S_{mj} = 20 \log V_s - 20 \log P_m, \quad P_m = P_{HFRP} + 24 \text{ dB}$$
+
+where:
+
+$20 \log V_s$ : Electric spectrum;
+
+$20 \log P_m$ : Acoustic spectrum at MRP.
+
+##### **Method 2**
+
+The sending sensitivity  $S_{mj}$  is given by the following relationship:
+
+$$S_{mj} = 20 \log V_s - 20 \log P_m - \text{Corr} - 24 \text{ dB}$$
+
+where:
+
+$20 \log V_s$ : Electric spectrum;
+
+$20 \log P_m$ : Acoustic spectrum recorded at MRP;
+
+$\text{Corr}$ : Correction factor ( $20 \log P_{MRP}/P_{HFRP}$ ) of the Artificial Mouth.
+
+#### A.2.1.2 Receiving
+
+Each loudspeaker shall be placed in turn in the test room as specified in A.1.1.2.
+
+The noise signal generator shall be connected to the input of the reference codec.
+
+The sensitivity at each 1/3 octave band shall be calculated by subtracting the spectrum of the electric signal from the acoustic spectrum at the measurement point.
+
+The measurement shall be repeated at the minimum and maximum position of the (manual) volume control, changing the input level accordingly. In case of devices not provided with manual volume control, the measurement shall be repeated for excitation levels of  $-30 \text{ dBm}_0$  and  $-15 \text{ dBm}_0$ .
+
+### A.2.2 Loudness rating
+
+#### A.2.2.1 Sending Loudness Rating
+
+The sending sensitivity shall be measured for each of the fourteen 1/3rd octave bands given in Table 1/P.79 [10], bands 4 to 17 (200 Hz-4 kHz). The sensitivity is expressed in terms of  $\text{dB(V/Pa)}$  and the SLR shall be calculated according to Formula A-23b/P.79, over bands 4 to 17 and using the sending weighting factors from Table A.2/P.79, adjusted by subtracting 0.3 dB from each value, using the sending sensitivity response of A.2.1.1.
+
+The measurement shall be carried out for each microphone, which shall be mounted as specified in A.1.1.1. In case of microphones intended to pick up the sounds coming from multiple directions (either omni-directional or steered devices), the extreme incidence angles on the horizontal plane (as stated by the manufacturer) shall be tested, as well as an intermediate incidence direction. If stated by the manufacturer, the nominal direction shall be used as intermediate. The testing angles actually used for measurements shall be stated in the test report.
+
+#### A.2.2.2 Receiving Loudness Rating
+
+The receiving sensitivity shall be measured for each of the fourteen 1/3rd octave bands given in Table 1/P.79 [10], bands 4 to 17 (200 Hz-4 kHz). The sensitivity is expressed in terms of  $\text{dB(Pa/V)}$  and the RLR shall be calculated according to Formula A-23c/P.79, over bands 4 to 17 and using the receiving weighting factors from Table A.2/P.79, adjusted by subtracting 0.3 dB from each value, using the receiving sensitivity response of A.2.1.2.
+
+The receiving sensitivity shall not be corrected by the  $L_e$  factor. The calculated RLR shall be corrected by subtracting 14 dB, according to ITU-T Rec. P.340 [5].
+
+### A.2.3 Terminal Coupling Loss
+
+The measurements shall be carried out by coupling, as specified in A.1.1.3, the most efficient loudspeaker with the most efficient microphone.
+
+#### A.2.3.1 Weighted Terminal Coupling Loss
+
+The test signal shall be a pink noise, with a level of  $(-15 - F_{\text{tcl}}) \text{ dBm}_0$ .
+
+The attenuation from digital input to digital output shall be measured at the 1/3rd octave frequencies given by the R10 series of preferred numbers in ISO 3 [11] for frequencies from 100 Hz to 8000 Hz.
+
+The  $\text{TCL}_w$  shall be calculated according to the method in B.4/G.122 [12] (trapezoidal rule), on the frequency band from 100 Hz to 8 kHz. The value calculated according to ITU-T Rec. G.122 [12] ( $\text{TCL}_{w\text{calculated}}$ ) shall be corrected by adding the correction factor  $F_{\text{tcl}}$  and by considering the total sound power produced by all the loudspeakers:
+
+$$\text{TCL}_w = \text{TCL}_{w\text{calculated}} + F_{\text{tcl}} - 10 \log \frac{n-1}{2}$$
+
+where  $n$  is the total number of loudspeakers equipping the terminal under test.
+
+NOTE – The formula above assumes that only one microphone is active at each time and that the sound pressure levels of signals picked up from the more distant loudspeakers is 3 dB less than the signal level generated by the better coupled loudspeaker. It is also assumed that a power summation law applies to the signals picked up by the different loudspeakers. This is not absolutely true in principle, but some uncorrelation of the sound signals generated by the different loudspeakers can be assumed to result from the different transmission path lengths and from the reverberation effects occurring in actual use.
+
+#### A.2.3.2 Stability loss
+
+The test signal shall be sinusoidal, with a level of  $(-15 - F_{\text{tel}})$  dBm0.
+
+The attenuation from digital input to digital output shall be measured at 1/24th octave intervals for frequencies from 100 Hz to 8 kHz. The actually measured values shall be corrected by adding  $F_{\text{tel}}$  and by subtracting  $10 \log [(n+1)/2]$  (as for the TCLw measurement).
+
+# APPENDIX I
+
+## Practical *in-situ* audio alignment procedure for multiple-users hands-free GATs
+
+## I.1 Introduction
+
+The hands-free function for a group of users is normally provided with audio arrangements which widely interact with the installation environment and a guide is provided here for *in-situ* aligning the electroacoustic sensitivities and checking the correct transduction across the whole frequency band.
+
+## I.2 Audio alignment and sensitivity-frequency characteristics
+
+Audio alignment is an operation carried out when the terminal is installed, and any time the acoustic configuration of GATs is changed. It is intended to guarantee the proper setting of sending and receiving level adjustments, in order to prevent the channel overloading while still guaranteeing adequate signal to noise and a comfortable receiving audio level.
+
+The following equipment should be used for performing the audio alignment of GAT terminals:
+
+- Artificial Mouth (complying with ITU-T Rec. P.51 [9]);
+- signal generator (digital or analogue);
+- sound level meter (complying with IEC 60651 [13]);
+- electric level meter.
+
+The acoustic test signal generated by the Artificial Mouth should consist of speech-shaped noise (ITU-T Rec. P.50 [14]), at a level of  $-4.7$  dBPa at the MRP.
+
+The signal generator is used for performing the receiving alignment and can either generate an encoded digital path at the digital interface of the GAT, or an analogue signal to be applied at a suitable analogue test point. In the latter case, a reference codec could be necessary for digital GATs if no specific interface for alignment purposes is available within the terminal. The signal for receiving alignment should be a speech-shaped noise (ITU-T Rec. P.50 [14]) at a level of  $-20$  dBm0. If necessary, the noise can be modulated ON-OFF. In this case, the signal level is defined as the level generated during the ON periods of the signal.
+
+NOTE – Terminal manufacturers are encouraged to implement an analogue 0 dBr interface for alignment purposes in their equipment.
+
+If no specific alignment interface is provided, the electric level meter for sending alignment should either directly process the digital pattern generated by the terminal, or be used in conjunction with a Reference Coder.
+
+### **I.2.1 Sending**
+
+#### **I.2.1.1 Sensitivity adjustment(s)**
+
+The Artificial Mouth should be placed over the border of the conference table, as shown in Figure A.1, in correspondence of each conferee position. The conference microphones should be positioned on the conference table (or in the conference room) as in normal use.
+
+If a sensitivity adjustment is provided for each microphone, it should be regulated in turn in order to achieve an output level of  $-20 \text{ dBm}0$  when the Mouth is placed in correspondence with the associated microphone. Otherwise, if only one sensitivity control is provided, it should be regulated in order that the average reading, obtained by placing the Mouth in correspondence of each conferee position in turn, is equal to  $-20 \text{ dBm}0$ .
+
+#### **I.2.1.2 *In-situ* frequency response**
+
+The *in-situ* measurement of the sending frequency response is defined as the difference between the octave spectra of the output signal and of the acoustic excitation signal at the MRP. Considering that the measurements are *in-situ*, the octave band analysis shall be restricted to the bandwidth from 125 Hz to 4 kHz (centre frequencies). It is recommended that the sum of the absolute differences between the measured values and their average is less than 8 dB.
+
+### **I.2.2 Receiving**
+
+#### **I.2.2.1 Sensitivity adjustment**
+
+The speech-shaped noise is fed to the input of the terminal at a level of  $-20 \text{ dBm}0$ . With the manual volume control (if any) at its maximum position, the receiving gain should be adjusted in order to achieve a sound pressure level of at least 54 dBA at each conferee position. The measurements should be made by placing the measurement microphone at point C (Figure A.1) corresponding to each conferee position, and in the absence of the Artificial Mouth.
+
+NOTE – Practical experience has shown that higher listening levels, up to 65 dBA, may be desirable. The maximum settable gain being constrained by the terminal stability limit.
+
+#### **I.2.2.2 *In-situ* frequency response**
+
+The *in-situ* measurement of the receiving frequency response is defined as the difference between the octave spectra of the output signal, and of the input excitation signal at the terminal interface. Considering that measurements are *in-situ*, the octave band analysis shall be restricted to the bandwidth from 125 Hz to 4 kHz (centre frequencies). It is recommended that the sum of the absolute differences between the measured values and their average is less than 12 dB.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                |
+|-----------------|--------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                              |
+| Series B        | Means of expression: definitions, symbols, classification                                                                      |
+| Series C        | General telecommunication statistics                                                                                           |
+| Series D        | General tariff principles                                                                                                      |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                              |
+| Series F        | Non-telephone telecommunication services                                                                                       |
+| Series G        | Transmission systems and media, digital systems and networks                                                                   |
+| Series H        | Audiovisual and multimedia systems                                                                                             |
+| Series I        | Integrated services digital network                                                                                            |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                    |
+| Series K        | Protection against interference                                                                                                |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant                                        |
+| Series M        | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                |
+| Series O        | Specifications of measuring equipment                                                                                          |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                            |
+| Series Q        | Switching and signalling                                                                                                       |
+| Series R        | Telegraph transmission                                                                                                         |
+| Series S        | Telegraph services terminal equipment                                                                                          |
+| Series T        | Terminals for telematic services                                                                                               |
+| Series U        | Telegraph switching                                                                                                            |
+| Series V        | Data communication over the telephone network                                                                                  |
+| Series X        | Data networks and open system communications                                                                                   |
+| Series Y        | Global information infrastructure and Internet protocol aspects                                                                |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                           |

marked/P/T-REC-P.310-200906-I_PDF-E/raw.md

@@ -0,0 +1,1177 @@
+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.310**
+
+(06/2009)
+
+SERIES P: TERMINALS AND SUBJECTIVE AND  
+OBJECTIVE ASSESSMENT METHODS
+
+Voice terminal characteristics
+
+---
+
+**Transmission characteristics for narrow-band  
+digital handset and headset telephones**
+
+Recommendation ITU-T P.310
+
+# ITU-T P-SERIES RECOMMENDATIONS **TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS**
+
+|                                                                                               |               |              |
+|-----------------------------------------------------------------------------------------------|---------------|--------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality | Series        | P.10         |
+| <b>Voice terminal characteristics</b>                                                         | <b>Series</b> | <b>P.30</b>  |
+|                                                                                               |               | <b>P.300</b> |
+| Reference systems                                                                             | Series        | P.40         |
+| Objective measuring apparatus                                                                 | Series        | P.50         |
+|                                                                                               |               | P.500        |
+| Objective electro-acoustical measurements                                                     | Series        | P.60         |
+| Measurements related to speech loudness                                                       | Series        | P.70         |
+| Methods for objective and subjective assessment of speech quality                             | Series        | P.80         |
+|                                                                                               |               | P.800        |
+| Audiovisual quality in multimedia services                                                    | Series        | P.900        |
+| Transmission performance and QoS aspects of IP end-points                                     | Series        | P.1000       |
+| Communications involving vehicles                                                             | Series        | P.1100       |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+## **Recommendation ITU-T P.310**
+
+# **Transmission characteristics for narrow-band digital handset and headset telephones**
+
+## **Summary**
+
+Recommendation ITU-T P.310 provides audio performance requirements and associated testing methods for narrow-band (300-3400 Hz) digital handset and headset telephones.
+
+Requirements and test methods are specified for the major audio transmission parameters including sending and receiving frequency response, loudness rating, noise, distortion, out-of-band signals, linearity, sidetone, echo and delay.
+
+This Recommendation is only applicable to digital telephones using encoding conforming to Recommendations ITU-T G.711 (64 kbit/s, PCM) and ITU-T G.726 (32 kbit/s, ADPCM). IP terminals and wireless headsets are not covered in this recommendation.
+
+## **Source**
+
+Recommendation ITU-T P.310 was approved on 22 June 2009 by ITU-T Study Group 12 (2009-2012) under Recommendation ITU-T A.8 procedures.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2010
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## CONTENTS
+
+|                                                                | Page |
+|----------------------------------------------------------------|------|
+| 1 Scope .....                                                  | 1    |
+| 2 References.....                                              | 1    |
+| 3 Definitions and abbreviations .....                          | 2    |
+| 3.1 Definitions .....                                          | 2    |
+| 3.2 Abbreviations .....                                        | 3    |
+| 4 Test configuration.....                                      | 4    |
+| 4.1 Measurement approaches for testing digital telephones..... | 4    |
+| 4.2 Test equipment .....                                       | 5    |
+| 4.3 Measurement set-up.....                                    | 6    |
+| 4.4 Test environment .....                                     | 7    |
+| 4.5 Test signal and level .....                                | 7    |
+| 4.6 Accuracy of test equipment .....                           | 7    |
+| 5 Handset technical requirements .....                         | 8    |
+| 5.1 Sending characteristics .....                              | 8    |
+| 5.2 Receiving characteristics .....                            | 14   |
+| 5.3 Sidetone characteristics .....                             | 20   |
+| 5.4 Echo path loss characteristics .....                       | 22   |
+| 5.5 Delay.....                                                 | 25   |
+| 6 Headset technical requirements .....                         | 25   |
+| 6.1 Sending characteristics .....                              | 25   |
+| 6.2 Receiving characteristics .....                            | 26   |
+| 6.3 Echo path loss characteristics .....                       | 26   |
+| Annex A – Distortion allowances .....                          | 28   |
+| Bibliography.....                                              | 29   |
+
+
+
+## Recommendation ITU-T P.310
+
+## Transmission characteristics for narrow-band digital handset and headset telephones
+
+# 1 Scope
+
+This Recommendation deals with sending and receiving frequency response, loudness rating, noise, distortion, out-of-band signals, linearity, sidetone, echo and delay of narrow-band (300-3400 Hz) digital handset and headset telephones using "Waveform" encoding according to [ITU-T G.711] (PCM at both 64 and 56 kbit/s) and [ITU-T G.726] (ADPCM, 32 kbit/s). IP terminals and wireless headsets are not covered in this Recommendation.
+
+The use of digital telephones using [ITU-T G.728] (LD-CELP, 16 kbit/s) and mobile/cordless telephones are under study.
+
+Requirements applicable to low acoustic impedance transducers and digital telephone sets using non-linear techniques are under study.
+
+The requirements listed in this Recommendation should also be used as the basis of requirements for other "waveform" encoding schemes.
+
+The values given in this Recommendation should be used for developing specifications which will include assigning tolerances, etc.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T G.122] Recommendation ITU-T G.122 (1993), *Influence of national systems on stability and talker echo in international connections.*
+- [ITU-T G.131] Recommendation ITU-T G.131 (2003), *Talker echo and its control.*
+- [ITU-T G.711] Recommendation ITU-T G.711 (1988), *Pulse code modulation (PCM) of voice frequencies.*
+- [ITU-T G.712] Recommendation ITU-T G.712 (2001), *Transmission performance characteristics of pulse code modulation channels.*
+- [ITU-T G.726] Recommendation ITU-T G.726 (1990), *40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM).*
+- [ITU-T G.728] Recommendation ITU-T G.728 (1992), *Coding of speech at 16 kbit/s using low-delay code excited linear prediction.*
+- [ITU-T I.412] Recommendation ITU-T I.412 (1988), *ISDN user-network interfaces – Interface structures and access capabilities.*
+- [ITU-T I.430] Recommendation ITU-T I.430 (1995), *Basic user-network interface – Layer 1 specification.*
+
+- [ITU-T O.41] Recommendation ITU-T O.41 (1994), *Psophometer for use on telephone-type circuits.*
+- [ITU-T O.131] Recommendation ITU-T O.131 (1988), *Quantizing distortion measuring equipment using a pseudo-random noise test signal.*
+- [ITU-T O.133] Recommendation ITU-T O.133 (1993), *Equipment for measuring the performance of PCM encoders and decoders.*
+- [ITU-T P.10] Recommendation ITU-T P.10/G.100 (2006), *Vocabulary for performance and quality of service.*
+- [ITU-T P.50] Recommendation ITU-T P.50 (1999), *Artificial voices.*
+- [ITU-T P.51] Recommendation ITU-T P.51 (1996), *Artificial mouth.*
+- [ITU-T P.57] Recommendation ITU-T P.57 (2009), *Artificial ears.*
+- [ITU-T P.58] Recommendation ITU-T P.58 (1996), *Head and torso simulator for telephonometry.*
+- [ITU-T P.64] Recommendation ITU-T P.64 (2007), *Determination of sensitivity/frequency characteristics of local telephone systems.*
+- [ITU-T P.79] Recommendation ITU-T P.79 (2007), *Calculation of loudness ratings for telephone sets.*
+- [ITU-T P.380] Recommendation ITU-T P.380 (2003), *Electro-acoustic measurements on headsets.*
+- [ITU-T P.501] Recommendation ITU-T P.501 (2007), *Test signals for use in telephonometry.*
+- [ITU-T P.502] Recommendation ITU-T P.502 (2000), *Objective test methods for speech communication systems using complex test signals.*
+- [ITU-T P.581] Recommendation ITU-T P.581 (2000), *Use of head and torso simulator (HATS) for hands-free terminal testing*
+- [ISO 3] ISO 3:1973, *Preferred numbers – Series of preferred numbers.*
+- [ISO 1996-1] ISO 1996-1:2003, *Acoustics – Description, measurement and assessment of environmental noise – Part 1: Basic quantities and assessment procedures.*
+
+# 3 Definitions and abbreviations
+
+## 3.1 Definitions
+
+This Recommendation defines the following terms:
+
+**3.1.1 0 dB reference point:** To preserve compatibility with existing codecs already in use in local digital switches, which are defined as a 0 dBr point, the codec (A- or  $\mu$ -law) should be defined as follows:
+
+- *D/A converter* – A digital test sequence (DTS) representing the PCM equivalent of an analogue sinusoidal signal whose r.m.s. value is 3.14 dB (A-law) or 3.17 dB ( $\mu$ -law) below the maximum full-loaded capacity of the codec will generate 0 dBm across a 600-ohm load. Here DTS is defined as a periodic sequence of character signals as given in [ITU-T G.711].
+- *A/D converter* – A 0 dBm signal generated from a 600-ohm source will give the digital test sequence representing the PCM equivalent of an analogue sinusoidal signal whose r.m.s. value is 3.14 dB (A-law) or 3.17 dB ( $\mu$ -law) below the maximum full load capacity of the codec.
+
+**3.1.2 acoustic reference level (ARL):** Defined as the acoustic level at MRP which results in a –10 dBm0 output at the digital interface.
+
+**3.1.3 digital telephone set (DT):** A digital telephone set is one in which the A/D and D/A converters are built in and the connection to the network is via a digital bitstream.
+
+**3.1.4 HATS position:** The HATS (head and torso simulator) position (see Annexes D and E of [ITU-T P.64]) is the correct handset position for measuring sensitivity and frequency response characteristics. The HATS position has been shown to be essentially identical to the LRGP (loudness rating guard-ring position), except for the mouth simulator direction, which has been corrected with a 19° downwards rotation to more closely match real talkers. For handsets with omnidirectional microphones, measurements on the two heads may differ slightly, typically less than 1 dB. For handsets with directional or noise-cancelling microphones, the differences will be larger, and the HATS position will give the more realistic results.
+
+## **3.2 Abbreviations**
+
+Relevant abbreviations in [ITU-T P.10] will apply.
+
+This Recommendation uses the following abbreviations:
+
+|                   |                                         |
+|-------------------|-----------------------------------------|
+| A/D               | Analogue-to-Digital                     |
+| ARL               | Acoustic Reference Level                |
+| D/A               | Digital-to-Analogue                     |
+| DRP               | earDrum Reference Point                 |
+| DTS               | Digital Test Sequence                   |
+| ERP               | Ear Reference Point                     |
+| ERUP              | Estimated Real Use Position             |
+| HATS              | Head And Torso Simulator                |
+| ISDN              | Integrated Services Digital Network     |
+| LRGP              | Loudness Rating Guard-ring Position     |
+| LSTR              | Listener SideTone Rating                |
+| MRP               | Mouth Reference Point                   |
+| PABX              | Private Automatic Branch Exchange       |
+| PCM               | Pulse Code Modulation                   |
+| RLR               | Receiving Loudness Rating               |
+| RTP               | Recommended Test Position               |
+| RWP               | Recommended Wearing Position            |
+| $S_{je}$          | Receiving Sensitivity (Artificial Ear)  |
+| $S_{JE}$          | Receiving Sensitivity (Real Ear)        |
+| SLR               | Sending Loudness Rating                 |
+| $S_{mj}$          | Sending Sensitivity (Artificial Mouth)  |
+| $S_{MJ}$          | Sending Sensitivity (Real Mouth)        |
+| $S_{si}$ (diff)   | Sending Sensitivities for diffuse sound |
+| $S_{si}$ (direct) | Sending Sensitivities for direct sound  |
+
+|              |                                                                           |
+|--------------|---------------------------------------------------------------------------|
+| STMR         | SideTone Masking Rating                                                   |
+| TCL          | Terminal Coupling Loss                                                    |
+| TCLw         | Weighted Terminal Coupling Loss                                           |
+| $\Delta S_m$ | Difference between the sending sensitivities for diffuse and direct sound |
+
+# 4 Test configuration
+
+## 4.1 Measurement approaches for testing digital telephones
+
+In general, there are two approaches for evaluating the transmission performance of a digital telephone, the direct approach and the codec approach. The direct approach is, in principle, the most accurate although the use of the codec approach may sometimes be advantageous.
+
+ITU-T recommends both methods to evaluate the voice transmission performance of a digital handset or headset telephone using "Waveform" encoding conforming to [ITU-T G.711] (PCM at 64 kbit/s and 56 kbit/s) and [ITU-T G.726] (ADPCM, 32 kbit/s).
+
+### 4.1.1 Direct digital processing approach
+
+In this approach, shown in Figure 4-1, the companded digital input/output bitstream of the telephone set is operated upon directly. The advantage is that most of the test signals, if sampled at 8 kHz, can be generated and analysed without the need for resampling and A/D or D/A conversion.
+
+![Figure 4-1: Digital telephone test arrangement (direct digital processing approach).](c2fc2621e8206d24427b56bcb2398fc0_img.jpg)
+
+The diagram shows a 'Digital set' enclosed in a dashed box. Inside, an input signal  $S_M$  enters a microphone symbol, followed by an A/D converter. An output signal  $S_E$  exits from a D/A converter. Both converters are connected to a 'Multi-plexer'. The 'Multi-plexer' is connected to an 'Interface' block outside the dashed box. The 'Interface' block receives a 'Control' signal from above and a 'PCM' signal from below. It is also connected to a 'Direct digital processing unit'.
+
+Figure 4-1: Digital telephone test arrangement (direct digital processing approach).
+
+Figure 4-1 – Digital telephone test arrangement  
+(direct digital processing approach)
+
+### 4.1.2 Codec approach
+
+In this approach, shown in Figure 4-2, a codec is used to convert the companded digital input/output bitstream of the telephone set to the equivalent analogue values, so that existing test procedures and equipment can be used. This codec should be a high-quality codec whose characteristics are as close as possible to ideal (see clause 4.2.2).
+
+![Figure 4-2: Digital telephone test arrangement (codec approach).](b10763be31553f31cbb795653b731a43_img.jpg)
+
+The diagram shows a 'Digital set' enclosed in a dashed box. Inside, an input signal  $S_M$  enters a microphone symbol, followed by an A/D converter. An output signal  $S_E$  exits from a D/A converter. Both converters are connected to a 'Multi-plexer'. The 'Multi-plexer' is connected to an 'interface' block outside the dashed box. The 'interface' block receives a 'Control' signal from above. It is connected to a '"Reference codec" test bed' (another dashed box). Inside this test bed, the signal from the interface goes to a D/A converter, which is followed by a  $600\ \Omega$  resistor. The signal from the D/A converter also goes to an A/D converter, which is preceded by a  $600\ \Omega$  resistor. Both A/D converters are connected to 'Analogue instruments'.
+
+Figure 4-2: Digital telephone test arrangement (codec approach).
+
+Figure 4-2 – Digital telephone test arrangement  
+(codec approach)
+
+NOTE – The digital telephone test equipment will, in general, be connected to the telephone under test through an interface. Such an interface should be able to provide all the signalling and supervisory sequences necessary for the telephone set to be working in all test modes. The interface must be capable of converting the digital output stream from the tested set (which may be in various formats, depending on the specific type of telephone set, e.g., conforming to [ITU-T I.412] for ISDN sets), to a form compatible with the test equipment. Interfaces can be applied for sending and receiving separately, taking into account telephone sets which are connected to various types of exchanges.
+
+## 4.2 Test equipment
+
+### 4.2.1 Electro-acoustic equipment
+
+The preferred acoustical access to terminals is the most realistic simulation of the "average" subscriber. This is made by using HATS (head and torso simulator) with appropriate ear simulator and appropriate means to fix handset or headset in a realistic and reproducible way. HATS, including the artificial mouth and the artificial ear, shall comply with [ITU-T P.58]. The recommended ear simulators are type 3.3 and type 3.4 artificial ear, described in [ITU-T P.57].
+
+The horizontal positioning of the HATS reference plane shall be guaranteed with  $\pm 2^\circ$ . The exact calibration and equalization of HATS can be found in [ITU-T P.581].
+
+### 4.2.2 Codecs
+
+#### 4.2.2.1 Ideal codec
+
+The ideal codec consists of an independent encoder and decoder whose characteristics are hypothetical and comply with [ITU-T G.711]. The ideal encoder is a perfect analogue-to-digital converter preceded by an ideal low-pass filter (assumed to have no attenuation/frequency distortion and no envelope-delay distortion), and may be simulated by a digital processor. The ideal decoder is a perfect digital-to-analogue converter followed by an ideal low-pass filter (assumed to have no attenuation/frequency distortion and no envelope-delay distortion), and which may be simulated by a digital processor<sup>1</sup>.
+
+For the measurement of the sending side of a telephone set, the output digital signal is converted by the decoder to an analogue signal. The electrical characteristics of this output signal are measured using conventional analogue instruments. For the measurement of the receiving side of a telephone set, the analogue output from a signal source is converted to a digital signal by the ideal encoder and fed to the receiving input of the digital telephone set.
+
+NOTE – For codecs conforming to [ITU-T G.726], a G.711/G.726 conversion will be applied.
+
+#### 4.2.2.2 Reference codec
+
+A practical implementation of an ideal codec may be called a reference codec (see [ITU-T O.133]).
+
+For the reference codec, characteristics such as attenuation/frequency distortion, idle channel noise, quantizing distortion, etc. should be better than the requirements specified in [ITU-T G.712], so as not to mask the corresponding parameters of the set under test. A suitable reference codec may be realized by using:
+
+- 1) at least 14-bit linear A/D and D/A converters of high quality, and transcoding the output signal to the A- or  $\mu$ -law PCM format;
+- 2) a filter response that meets the requirements of Figure 4-3.
+
+---
+
+<sup>1</sup> This characteristic can be realized, for example, using over-sampling techniques and digital filters.
+
+![Figure 4-3: Attenuation/frequency distortion of the sending or receiving sides of the reference codec. The graph shows Loss (dB) on the y-axis (ranging from -0.25 to 40) versus Frequency (Hz) on the x-axis (logarithmic scale from 80 to 4000). The loss is 0.0 dB from 80 Hz to 100 Hz, then drops to -0.25 dB at 100 Hz. It remains at -0.25 dB until 3000 Hz, where it steps up to 0.25 dB. At 3400 Hz, it steps up to 0.9 dB. At 3600 Hz, it drops back to -0.25 dB. At 4000 Hz, it steps up to 40 dB. Shaded regions indicate the allowed loss limits.](36ac3e730a00d3f42d3400f5709f641a_img.jpg)
+
+Figure 4-3: Attenuation/frequency distortion of the sending or receiving sides of the reference codec. The graph shows Loss (dB) on the y-axis (ranging from -0.25 to 40) versus Frequency (Hz) on the x-axis (logarithmic scale from 80 to 4000). The loss is 0.0 dB from 80 Hz to 100 Hz, then drops to -0.25 dB at 100 Hz. It remains at -0.25 dB until 3000 Hz, where it steps up to 0.25 dB. At 3400 Hz, it steps up to 0.9 dB. At 3600 Hz, it drops back to -0.25 dB. At 4000 Hz, it steps up to 40 dB. Shaded regions indicate the allowed loss limits.
+
+**Figure 4-3 – Attenuation/frequency distortion of the sending or receiving sides of the reference codec**
+
+##### 4.2.2.2.1 Analogue interface
+
+The output and input impedances return loss and longitudinal conversion losses of the analogue interface of the reference codec should be in accordance with [ITU-T O.133].
+
+##### 4.2.2.2.2 Digital interface
+
+The fundamental requirements for the reference codec digital interface are given in the appropriate ITU-T Recommendations (e.g., [ITU-T I.430] for ISDN telephone sets).
+
+## 4.3 Measurement set-up
+
+All measurements are performed using a HATS. The type of ear simulator and application force shall be indicated in a test report. For handsets, if not stated otherwise, 8N application force shall be used to apply the handset against the artificial ear.
+
+Proper positioning of handsets on HATS can be found in Annexes D and E of [ITU-T P.64].
+
+Suggestions for positioning headsets on HATS are given in [ITU-T P.380]. The manufacturer should provide the recommended wearing position (RWP) in the user's guide, which describes a precise way the device should be placed on the user's head. From RWP, the recommended test position (RTP) information can be derived, as close as possible to RWP. Also the RTP description can be provided by the manufacturer which includes the information how the receiving part of the headset should be placed against or inside the ear simulator, and further describes the positioning and orientation of the microphone. If neither RTP nor RWP are provided by the manufacturer, the headset shall be tested in the estimated real use position (ERUP). The test lab shall define an ERUP that closely approximates real use. Natural headband pressure, or other positioning techniques normally used by a real user, shall be used. Because the headset position may affect test results, the test shall be repeated at least 5 times by completely repositioning the headset, following the rules described in [ITU-T P.380].
+
+Use of the codec test approach means that test procedures for digital telephone sets in general follow those for analogue sets (see [ITU-T P.64]).
+
+The reference codec should meet the requirements of clause 4.2.2.2. An important difference, however, concerns the test circuits themselves (see Figures 5-2 and 5-4 to 5-7).
+
+The set is connected to the interface and is placed in the active call state.
+
+Handsets or headsets fitted with a volume control on receiving shall be set as close as possible to the nominal RLR and any residential difference from the nominal value will be corrected by the normalization process.
+
+## **4.4 Test environment**
+
+The test laboratory shall ensure that all measurements performed in the test room give identical results to those obtained in a free-field environment (e.g., an anechoic room).
+
+The environmental conditions for testing handset and headset terminals are specified as follows:
+
+- The test room shall be practically free-field down to a lowest frequency of 275 Hz, the handset or headset coupled with the HATS shall lie totally within this free-field volume. This is met if deviations from the ideal free-field conditions are less than  $\pm 1$  dB.
+- The ambient noise level shall be less than  $-64$  dBPa(A) for all the tests, except for tests requesting the generation of ambient noise, e.g., D-Factor measurement.
+- The test environment shall be free of mechanical disturbances.
+
+## **4.5 Test signal and level**
+
+In general, the test signals as described in this Recommendation should be applied. The use of the proposed test signals requires a linear and time invariant operation of the equipment under test. This cannot be ensured in all cases. For devices where the transmission properties are level and signal-dependent, alternative test signals should be chosen. In this case a more speech-like test signal such as described in [ITU-T P.50] and [ITU-T P.501] should be applied. Test house and manufacturer should ensure that the appropriate type of test signal is chosen.
+
+Unless stated otherwise, the test signal shall be set to  $-4.7$  dBPa at MRP for the sending direction and  $-16$  dBm0 for the receiving direction. The spectrum of acoustic signal produced by the artificial mouth is calibrated under free-field conditions at MRP.
+
+For a correct activation of the system, an artificial voice according to [ITU-T P.50] or a speech like test signal as described in [ITU-T P.501] shall be used for activation. The level of this activation signal shall be  $-4.7$  dBPa at MRP.
+
+The use of test signals and levels should be stated in the test report.
+
+NOTE 1 – The use of sine signals may not be appropriate when speech processing and coding systems are implemented in the terminal. For example, in distortion measurement, if a sine wave is not usable, an alternative test signal could be a band-limited noise signal centred on the test frequencies.
+
+NOTE 2 – It should be ensured that the test signal is treated by speech processing algorithms as a speech-like signal, and not a noise-like signal.
+
+NOTE 3 – When measuring digital telephone sets, it is advisable to avoid measuring at sub-multiples of the sampling frequency. There is a tolerance on the frequencies of  $\pm 2\%$  which may be used to avoid this problem, except for 4 kHz where only the  $-2\%$  tolerance may be used.
+
+## **4.6 Accuracy of test equipment**
+
+Unless specified otherwise, the accuracy of the measurements made by the test equipment shall be better than those given in Table 1.
+
+**Table 1 – Minimum measurement accuracy**
+
+| Quantity                     | Accuracy                                                                           |
+|------------------------------|------------------------------------------------------------------------------------|
+| Electrical signal power      | ±0.2 dB for levels ≥ -50 dBm<br>±0.4 dB for levels < -50 dBm                       |
+| Sound pressure               | ±0.7 dB                                                                            |
+| Time                         | ±5%                                                                                |
+| Frequency                    | ±0.2%                                                                              |
+| Sound pressure level at MRP  | ±3 dB for 100 Hz to 200 Hz<br>±1 dB for 200 Hz to 4 Hz<br>±3 dB for 4 kHz to 8 kHz |
+| Electrical excitation levels | ±0.4 dB (see Note 1)                                                               |
+| Frequency generation         | ±0.2% (see Note 2)                                                                 |
+
+NOTE 1 – Across the whole frequency range.  
+NOTE 2 – When measuring sampled systems, it is advisable to avoid measuring at sub-multiples frequency. There is a tolerance of ±2% on the generated frequencies, which may be used to avoid this problem, except for 4 kHz where only the -2% tolerance may be used.
+
+# 5 Handset technical requirements
+
+## 5.1 Sending characteristics
+
+### 5.1.1 Sending frequency response
+
+In view of the following consideration:
+
+- Unlike other standards, this Recommendation does not use ERP as the reference point for receiving, but uses the diffuse-field instead. With the concept of diffuse-field based receive measurements, a rising slope for the overall frequency response is achieved by a flat target frequency response in sending and a diffuse-field based receiving frequency response; the sensitivity mask of Table 2 is recommended.
+
+**Table 2 – Sending frequency response**
+
+| Frequency (Hz) | Upper limit (dB) | Lower limit (dB) |
+|----------------|------------------|------------------|
+| 100            | -18              |                  |
+| 300            | 5                | -5               |
+| 3400           | 5                | -5               |
+| 4000           | 5                |                  |
+
+NOTE – The limits for intermediate frequencies lie on a straight line drawn between the given values on a linear (dB) – logarithmic (Hz) scale.
+
+![Figure 5-1: Sending mask graph showing dB vs Frequency (Hz).](71ab4df17511d75261da8d462d643b1a_img.jpg)
+
+| Frequency (Hz) | Upper Limit (dB) | Lower Limit (dB) |
+|----------------|------------------|------------------|
+| 100            | -19              | -                |
+| 200            | 5                | -19              |
+| 300            | 5                | -5               |
+| 400            | 5                | 0                |
+| 3400           | 5                | 0                |
+| 4000           | 5                | -5               |
+| 4000+          | -                | -20              |
+
+Figure 5-1: Sending mask graph showing dB vs Frequency (Hz).
+
+Figure 5-1 – Sending mask
+
+#### 5.1.1.1 Measurement method
+
+The sending frequency characteristic is measured according to [ITU-T P.64] using the measurement set-up shown in Figure 5-1.
+
+A sinewave or an artificial speech (e.g., as specified in [ITU-T P.50] and [ITU-T P.501]) generator and a spectrum analyser should be used. Additional test methods may be found in [ITU-T P.502]. The test signal level shall be  $-4.7$  dBPa at MRP. The test signal level is averaged over the complete test signal sequence. The sensitivity is expressed in terms of dBV/Pa.
+
+![Figure 5-2: Block diagram of the measurement setup for sending frequency characteristic.](9b6b5924b48bf2fd5f347f88f06f45b3_img.jpg)
+
+```
+
+graph LR
+    SG[Signal generator] --> AM[Artificial mouth]
+    subgraph QR[Quiet room]
+        AM --> DT[Digital telephone]
+    end
+    DT --> IF[Interface]
+    C[Control] --> IF
+    IF --> TB[Test bed]
+    subgraph TB[Test bed]
+        DA[D/A]
+    end
+    DA --> R[600 Ω]
+    DA --> MA[Measuring amplifier]
+    MA --> LRD[Level recorder or distortion meter]
+
+```
+
+Figure 5-2: Block diagram of the measurement setup for sending frequency characteristic.
+
+Figure 5-2 – Measurements of sending frequency characteristic, HATS position
+
+### 5.1.2 Sending loudness rating (SLR)
+
+– The nominal value of SLR shall be  $\pm 8$  dB, with a tolerance of  $\pm 3$  dB.
+
+#### 5.1.2.1 Measurement method
+
+This should be calculated from the sensitivity/frequency characteristic determined in clause 5.1.1.1 by means of [ITU-T P.79].
+
+NOTE – Other methods for calculating loudness ratings used by some Administrations for their own internal planning purposes can be found in [b-Teleph].
+
+### 5.1.3 Sending noise
+
+In view of the following considerations:
+
+- compatibility with coder and decoder requirements according to [ITU-T G.712];
+- certain additions of noise must be allowed for in the electrical and acoustical parts (see clause 4.6);
+- compatibility with existing analogue telephones,
+
+the following limits are recommended.
+
+- sending noise level: maximum –64 dBm0p;
+- no peaks in any 1/3-octave band, with the level of 10 dB higher than the average noise spectrum in the frequency domain, shall occur.
+
+NOTE – The noise levels are related to the long-term objective for SLR and RLR.
+
+#### 5.1.3.1 Measurement method
+
+The sending noise shall be measured in a quiet environment as defined in clause 4.4.
+
+After a correct activation, the noise level at the digital output is measured in the frequency range from 100 Hz to 4000 Hz with apparatus including psophometric weighting described in [ITU-T O.41].
+
+NOTE – The ambient noise criterion will be met if the ambient noise does not exceed NR20 [ISO 1996-1].
+
+### 5.1.4 Sending distortion
+
+In view of the following considerations:
+
+- compatibility with coder and decoder requirements according to [ITU-T G.712];
+- certain additions of distortion must be allowed for in the electrical and acoustical parts (see clause 4.6);
+- compatibility with existing analogue telephones,
+
+two different sets of values are recommended relating to two different measuring methods (the "Sinewave" method and the "Noise" method; see [ITU-T G.712]). Either is acceptable.
+
+NOTE – ETSI have found it desirable to use both the noise method and the sinewave method for the following reasons:
+
+- The "Sinewave" method is effective for the measurement of the coding distortion and overload distortion.
+- The "Noise" method, being more speech-like and of lower frequency content, is more likely to indicate imperfections, including inter-modulation distortion, in the transducers as well as the coding.
+
+#### 5.1.4.1 Sending distortion using "Noise" method
+
+The "Noise" method is used routinely for A-law codecs.
+
+The ratio of signal-to-total distortion (harmonic and quantizing) power of the digitally encoded signal output by the terminal equipment measured with the proper noise weighting (see [ITU-T O.41]) shall be above the limits given in Tables 3 and 4 for [ITU-T G.711] (64 kbit/s) and [ITU-T G.726] (32 kbit/s), respectively.
+
+Limits for intermediate levels are found by drawing straight lines between the breaking points in the table on a linear (dB signal level) – linear (dB ratio) scale.
+
+**Table 3 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 64 kbit/s) for "Noise" method**
+
+| <b>Sending level dBPa<br/>at MRP</b> | <b>Sending ratio<br/>(dB)</b> |
+|--------------------------------------|-------------------------------|
+| –45                                  | 5.0                           |
+| –30                                  | 20.0                          |
+| –24                                  | 25.5                          |
+| –17                                  | 30.2                          |
+| –10                                  | 32.4                          |
+| 0                                    | 33.0                          |
+| +4                                   | 33.0                          |
+
+**Table 4 – Limits for signal-to-total distortion ratio  
+([ITU-T G.726], 32 kbit/s) for "Noise" method**
+
+| <b>Sending level dBPa<br/>at MRP</b> | <b>Sending ratio<br/>(dB)</b> |
+|--------------------------------------|-------------------------------|
+| –45                                  | 5.0                           |
+| –30                                  | 20.0                          |
+| –24                                  | 25.3                          |
+| –17                                  | 29.7                          |
+| –10                                  | 31.6                          |
+| 0                                    | 32.1                          |
+| +4                                   | 32.1                          |
+
+##### **5.1.4.1.1 Measurement method**
+
+The input at MRP is a band-limited noise signal corresponding to [ITU-T O.131]. The test signal is then applied at –45, –40, –35, –30, –24, –20, –17, –10, –5, 0, 4 dBPa.
+
+The ratio of the signal-to-total distortion power of the digital signal output with a psophometric noise weighting according to [ITU-T O.41] is measured (see [ITU-T O.131]).
+
+##### **5.1.4.1.2 Sending distortion using "Sinewave" method**
+
+The ratio of signal-to-total distortion power measured with the proper noise weighting (see [ITU-T O.41]) shall be above the limits given in Tables 5, 6 and 7 for [ITU-T G.711] (64 kbit/s), [ITU-T G.711] (56 kbit/s) and [ITU-T G.726] (32 kbit/s) respectively. The input sound pressure level is limited at +10 dBPa for this measurement.
+
+Limits for intermediate levels are found by drawing straight lines between the breaking points in the table on a linear (dB signal level) – linear (dB ratio) scale.
+
+**Table 5 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 64 kbit/s) for "Sinewave" method**
+
+| <b>Frequency<br/>(Hz)</b> | <b>Sending level<br/>(dBPa at MRP)</b> | <b>Sending ratio<br/>(dB)</b> |
+|---------------------------|----------------------------------------|-------------------------------|
+| 315                       | -4.7                                   | 26                            |
+| 510                       | -4.7                                   | 30.5                          |
+| 1020                      | -35                                    | 17.5                          |
+|                           | -30                                    | 22.5                          |
+|                           | -20                                    | 30.7                          |
+|                           | -10                                    | 33.3                          |
+|                           | 0                                      | 33.7                          |
+|                           | +7                                     | 31.7                          |
+|                           | +10                                    | 25.5                          |
+
+**Table 6 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 56 kbit/s) for "Sinewave" method**
+
+| <b>Sending level<br/>(dBPa at MRP)</b> | <b>Sending ratio<br/>(dB)</b> |
+|----------------------------------------|-------------------------------|
+| -35                                    | 15.3                          |
+| -30                                    | 20.3                          |
+| -20                                    | 27.5                          |
+| -10                                    | 28.5                          |
+| 0                                      | 28.6                          |
+| +7                                     | 27.9                          |
+| +10                                    | 24.2                          |
+
+**Table 7 – Limits for signal-to-total distortion ratio  
+([ITU-T G.726], 32 kbit/s) for "Sinewave" method**
+
+| <b>Sending level<br/>(dBPa at MRP)</b> | <b>Sending ratio<br/>(dB)</b> |
+|----------------------------------------|-------------------------------|
+| -35                                    | 17.3                          |
+| -30                                    | 22.3                          |
+| -20                                    | 29.3                          |
+| -10                                    | 31.1                          |
+| 0                                      | 31.3                          |
+| +7                                     | 30.0                          |
+| +10                                    | 25.0                          |
+
+###### 5.1.4.2.1 Measurement method
+
+After a correct activation of the system, a sinewave signal at frequencies of 315, 510 and 1020 Hz is applied at MRP respectively. The signal level shall be calibrated to  $-4.7$  dBPa at MRP for all frequencies, except for the sinewave signal with a frequency of 1020 Hz that shall be applied at MRP at the following levels:  $-35, -30, -25, -20, -15, -10, -5, 0, 7, 10$  dBPa. The input sound pressure level is limited at  $+10$  dBPa for this measurement.
+
+The ratio of the signal-to-total distortion power of the digital signal output is measured with a psophometric noise weighting according to [ITU-T O.41].
+
+NOTE – In cases where the sound pressure exceeds  $+6$  dBPa, the linearity of the artificial mouth should be checked as it exceeds the ITU-T P.51 limits. For good performance, in this case, it is recommended to use a suitable individual precalibration of the artificial mouth for compensation of the deviation of the measured data by taking into account the calibration results.
+
+### 5.1.5 Sending out-of-band signals
+
+In view of the following considerations:
+
+- compatibility with coder and decoder requirements according to [ITU-T G.712];
+- compatibility with existing practices in the mixed analogue-digital network in use today,
+
+the following limits are recommended:
+
+With any sinewave signal above 4.6 kHz and up to 8 kHz applied at MRP at a level of  $-4.7$  dBPa, the level of any image frequency produced at the digital interface shall be below a reference level obtained at 1020 Hz ( $-4.7$  dBPa at MRP) by at least the amount (in dB) specified in Table 8.
+
+**Table 8 – Discrimination levels – Sending out-of-band signals**
+
+| Applied sinewave frequency<br>(kHz) | Limit (minimum)<br>(dB) (Note) |
+|-------------------------------------|--------------------------------|
+| 4.6                                 | 30                             |
+| 8.0                                 | 40                             |
+
+NOTE – The limit at intermediate frequencies lies on a straight line drawn between the given values on a log (frequency) – linear (dB) scale.
+
+#### 5.1.5.1 Measurement method
+
+The reference signal used is an activation signal followed by a sine wave at 1020 Hz. The reference signal is applied at MRP ( $-4.7$  dBPa at MRP). The level is measured at the digital interface.
+
+The actual test signals used are an activation signal followed by a sine wave with the frequencies of 4.65 kHz, 5 kHz, 6 kHz, 6.5 kHz, 7 kHz and 7.5 kHz ( $-4.7$  dBPa at MRP) respectively. The level of any image frequencies at the digital interface is measured.
+
+### 5.1.6 Sending linearity
+
+Considering that some non-linear techniques may be used in digital telephones, for example:
+
+- automatic gain control;
+- compressor/expander techniques,
+
+these devices may be deliberately designed non-linear over the input level range specified, and may have dynamic characteristics (e.g., attack and hangover time).
+
+For digital telephones that are intended to have linear input-versus-output characteristics, the linearity relative to the gain for ARL should remain within the limits given in Table 9. For intermediate levels, the same limits for gain variation apply.
+
+**Table 9 – Sending linearity**
+
+| <b>Sending dB relative to ARL</b> | <b>Upper limit (dB)</b> | <b>Lower limit (dB)</b> |
+|-----------------------------------|-------------------------|-------------------------|
+| 13                                | 0.5                     | –0.5                    |
+| 0                                 | 0.5                     | –0.5                    |
+| –30                               | 0.5                     | –0.5                    |
+| –30                               | 1                       | – $\infty$              |
+| –40                               | 1                       | – $\infty$              |
+| <–40                              | 2                       | – $\infty$              |
+
+NOTE 1 – In cases where the sound pressure at MRP exceeds +6 dBPa, the linearity of the artificial mouth should be checked, as it exceeds the ITU-T P.51 limits. For good performance, in this case, it is recommended to use a suitable individual pre-calibration of the artificial mouth for compensation of the deviation of the measured data by taking into account the calibration results.
+
+NOTE 2 – If a digital telephone has specifically designed non-linear characteristics, alternative test methods based on more complex test signals may be needed for these tests. The principles are described in [ITU-T P.501] and [ITU-T P.502].
+
+#### **5.1.6.1 Measurement method**
+
+After a correct activation of the system, a sinewave signal with a frequency in the range 1004 Hz to 1025 Hz is applied at MRP. The level of this signal is adjusted until the output of the terminal is –10 dBm0. The level of the signal at MRP is then the ARL.
+
+The test signal shall be applied at the following levels:
+
+–45, –40, –35, –30, –25, –20, –15, –10, –5, 0, 5, 10, 13 dB relative to ARL.
+
+The variation of gain relative to the gain for ARL is measured.
+
+NOTE 1 – If the sinewave techniques cannot be used (which is likely if the terminal has a noise reduction device), another appropriate technique should be applied. For example, an artificial speech generator (e.g., as specified in [ITU-T P.50] and [ITU-T P.501]) and a spectrum analyser can be used. The test signal used shall be specified in the test report.
+
+NOTE 2 – Selective measurements may be used to avoid the effects of ambient noise.
+
+## **5.2 Receiving characteristics**
+
+### **5.2.1 Receiving frequency response**
+
+In view of the following consideration:
+
+- Unlike other standards, this Recommendation does not use ERP as the reference point for receiving, but uses the diffuse-field instead. With the concept of diffuse-field based receive measurements, a rising slope for the overall frequency response is achieved by a flat target frequency response in sending and a diffuse-field based receiving frequency response; the sensitivity mask of Table 10 is recommended.
+
+**Table 10 – Receiving frequency response**
+
+| Frequency (Hz) | Upper limit (dB) | Lower limit (dB) |
+|----------------|------------------|------------------|
+| 100            | 4                |                  |
+| 300            | 4                | -4               |
+| 3400           | 4                | -4               |
+| 4000           | 4                |                  |
+
+NOTE – The limit curves shall be determined by straight lines joining successive coordinates given in the table, where frequency response is plotted on a linear dB scale against frequency on a logarithmic scale. It is a floating or 'best fit' mask.
+
+![Graph showing the receiving mask with HATS, diffuse-field equalized. The Y-axis is dB from -20 to 10. The X-axis is Frequency in Hz on a logarithmic scale from 100 to 10,000. A red curve shows the mask boundary, and a black line shows the measured response. The graph is labeled P.310(09)_F5.3.](ebce355620876e10f907f8b71926c112_img.jpg)
+
+The figure is a line graph on a semi-logarithmic scale. The vertical axis (Y-axis) represents gain in dB, ranging from -20 to 10 in increments of 5. The horizontal axis (X-axis) represents frequency in Hz on a logarithmic scale, with major markers at 100, 1000, and 10,000 Hz. A red curve represents the 'receiving mask' boundary. It starts at -20 dB at 100 Hz, rises steeply to 0 dB at approximately 200 Hz, remains flat at 0 dB until about 3000 Hz, and then drops sharply back to -20 dB at 4000 Hz. A black line represents the 'measured response'. It starts at 4 dB at 100 Hz, remains flat until 300 Hz, drops to -3 dB at 300 Hz, remains flat until 3400 Hz, and then drops sharply to -20 dB at 4000 Hz. Small black diamonds mark the corner points of the response at (100, 4), (300, -3), (3400, -3), and (4000, -20). The text 'P.310(09)\_F5.3' is located in the bottom right corner of the plot area.
+
+Graph showing the receiving mask with HATS, diffuse-field equalized. The Y-axis is dB from -20 to 10. The X-axis is Frequency in Hz on a logarithmic scale from 100 to 10,000. A red curve shows the mask boundary, and a black line shows the measured response. The graph is labeled P.310(09)\_F5.3.
+
+**Figure 5-3 – Receiving mask with HATS, diffuse-field equalized**
+
+#### **5.2.1.1 Measurement method**
+
+The receiving frequency characteristic is measured according to [ITU-T P.64] using the measurement set-up shown in Figure 5-4.
+
+A sinewave or an artificial speech generator (e.g., as specified in [ITU-T P.50] and [ITU-T P.501]), a spectrum analyser and a diffuse-field equalized HATS are used. Additional test methods may be found in [ITU-T P.502]. The test signal level shall be -16.0 dBm0, measured at the digital reference point or the equivalent analogue point. The test signal level is averaged over the complete test signal sequence. The sensitivity is expressed in terms of dBPa/V, referred to the HATS Reference Point (HRP). Information about HATS diffuse-field frequency response is available in [ITU-T P.58].
+
+![Figure 5-4: Measurement of receiving frequency characteristic, HATS position. The diagram shows a 'Quiet room' (dashed box) containing an 'Artificial ear', a 'Digital telephone', and a 'Measuring amplifier'. The 'Measuring amplifier' is connected to a 'Level recorder or distortion meter'. The 'Digital telephone' is connected to an 'Interface', which is also connected to a 'Control'. The 'Interface' is connected to a 'Test bed' containing an 'A/D' converter. The 'A/D' converter is connected to a 'Signal generator' and a '600 Ω' resistor.](e69b9188aa2c14ec6b21c83f711fef65_img.jpg)
+
+```
+
+graph LR
+    subgraph Quiet_room [Quiet room]
+        AE[Artificial ear] --- DT[Digital telephone]
+        MA[Measuring amplifier] --- AE
+    end
+    DT --- Interface
+    Control --- Interface
+    Interface --- Test_bed[Test bed]
+    subgraph Test_bed_sub [Test bed]
+        AD[A/D]
+    end
+    AD --- SG[Signal generator]
+    SG --- R[600 Ω]
+    R --- AD
+    MA --- LDM[Level recorder or distortion meter]
+
+```
+
+Figure 5-4: Measurement of receiving frequency characteristic, HATS position. The diagram shows a 'Quiet room' (dashed box) containing an 'Artificial ear', a 'Digital telephone', and a 'Measuring amplifier'. The 'Measuring amplifier' is connected to a 'Level recorder or distortion meter'. The 'Digital telephone' is connected to an 'Interface', which is also connected to a 'Control'. The 'Interface' is connected to a 'Test bed' containing an 'A/D' converter. The 'A/D' converter is connected to a 'Signal generator' and a '600 Ω' resistor.
+
+P.310(09)\_F5.4
+
+**Figure 5-4 – Measurement of receiving frequency characteristic, HATS position**
+
+### 5.2.2 Receiving loudness rating (RLR)
+
+- The nominal value of RLR shall be +2 dB, with a tolerance of  $\pm 3$  dB
+
+#### 5.2.2.1 Measurement method
+
+This should be calculated from the sensitivity/frequency characteristic determined in clause 5.2.1.1 by means of [ITU-T P.79]. The DRP-ERP correction as defined in [ITU-T P.57] is applied.
+
+NOTE – Other methods for calculating loudness rating used by some Administrations for their own internal planning purposes can be found in [b-Teleph].
+
+### 5.2.3 Receiving noise
+
+When driven by a signal corresponding to a decoder value quiet code, the maximum acoustic noise level at ERP shall be as follows:
+
+- if no user-controlled volume control is provided or when the volume control is set to nominal RLR value, the measured receiving noise at ERP shall not be greater than  $-57$  dBPa(A);
+- if a volume control is provided, the measured receiving noise at ERP shall not be greater than  $-54$  dBPa(A) at the maximum setting of the volume control;
+- no peaks in any 1/3-octave band with the level of 10 dB higher than the average noise spectrum in the frequency domain shall occur.
+
+#### 5.2.3.1 Measurement method
+
+The receiving noise shall be measured in a quiet environment as defined in clause 4.4.
+
+The receiving noise level at ERP is measured with A-weighting. The DRP-ERP correction as defined in [ITU-T P.57] is applied.
+
+### 5.2.4 Receiving distortion
+
+#### 5.2.4.1 Receiving distortion using "Noise" method
+
+The ratio of signal-to-total distortion (harmonic and quantizing) power of the signal measured at ERP with A-weighting shall be above the limits given in Tables 11 and 12 for [ITU-T G.711] (64 kbit/s) and [ITU-T G.726] (32 kbit/s), respectively, unless the signal in the artificial ear exceeds  $+5$  dBPa or is less than  $-50$  dBPa.
+
+Limits for intermediate levels are found by drawing straight lines between the breaking points in the table on a linear (dB signal level) – linear (dB ratio) scale.
+
+**Table 11 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 64 kbit/s) for "Noise" method**
+
+| <b>Receiving level<br/>at the digital interface<br/>(dBm0)</b> | <b>Receiving ratio<br/>(dB)</b> |
+|----------------------------------------------------------------|---------------------------------|
+| –55                                                            | 5.0                             |
+| –40                                                            | 20.0                            |
+| –34                                                            | 25.0                            |
+| –27                                                            | 30.6                            |
+| –20                                                            | 33.0                            |
+| –10                                                            | 33.7                            |
+| –6                                                             | 33.8                            |
+| –3                                                             | 24.0                            |
+
+**Table 12 – Limits for signal-to-total distortion ratio  
+([ITU-T G.726], 32 kbit/s) for "Noise" method**
+
+| <b>Receiving level<br/>at the digital interface<br/>(dBm0)</b> | <b>Receiving ratio<br/>(dB)</b> |
+|----------------------------------------------------------------|---------------------------------|
+| –55                                                            | 5.0                             |
+| –40                                                            | 20.0                            |
+| –34                                                            | 24.8                            |
+| –27                                                            | 30.1                            |
+| –20                                                            | 32.3                            |
+| –10                                                            | 32.9                            |
+| –6                                                             | 32.9                            |
+| –3                                                             | 23.4                            |
+
+##### **5.2.4.1.1 Measurement method**
+
+A digitally simulated band-limited noise signal corresponding to [ITU-T O.131] is applied to the digital interface at the following levels: –55, –50, –45, –40, –34, –30, –27, –20, –15, –10, –6, –3 dBm0.
+
+The total distortion power shall be measured at ERP with A-weighting. The ratio of the signal-to-total distortion power is calculated (see [ITU-T O.131]). The DRP-ERP correction defined in [ITU-T P.57] is applied.
+
+#### **5.2.4.2 Receiving distortion using the "Sinewave" method**
+
+The ratio of signal-to-total distortion power measured at ERP with A-weighting shall be above the limits given in Tables 13, 14 and 15 for [ITU-T G.711] (64 kbit/s), [ITU-T G.711] (56 kbit/s) and [ITU-T G.726] (32 kbit/s) respectively, unless the signal in the artificial ear exceeds +10 dBPa or is less than –50 dBPa.
+
+Limits for intermediate levels are found by drawing straight lines between the breaking points in the table on a linear (dB signal level) – linear (dB ratio) scale.
+
+**Table 13 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 64 kbit/s) for "Sinewave" method**
+
+| <b>Frequency<br/>(Hz)</b> | <b>Receiving level<br/>at the digital interface<br/>(dBm0)</b> | <b>Receiving ratio<br/>(dB)</b> |
+|---------------------------|----------------------------------------------------------------|---------------------------------|
+| 315                       | -16                                                            | 20                              |
+| 510                       | -16                                                            | 30.5                            |
+| 1020                      | -45                                                            | 17.5                            |
+|                           | -40                                                            | 22.5                            |
+|                           | -30                                                            | 30.5                            |
+|                           | -20                                                            | 33.0                            |
+|                           | -10                                                            | 33.5                            |
+|                           | -3                                                             | 31.2                            |
+|                           | 0                                                              | 25.5                            |
+
+**Table 14 – Limits for signal-to-total distortion ratio  
+([ITU-T G.711], 56 kbit/s) for "Sinewave" method**
+
+| <b>Receiving level at<br/>the digital interface<br/>(dBm0)</b> | <b>Receiving ratio<br/>(dB)</b> |
+|----------------------------------------------------------------|---------------------------------|
+| -45                                                            | 15.3                            |
+| -40                                                            | 20.3                            |
+| -30                                                            | 27.4                            |
+| -20                                                            | 28.4                            |
+| -10                                                            | 28.6                            |
+| -3                                                             | 27.7                            |
+| 0                                                              | 24.2                            |
+
+**Table 15 – Limits for signal-to-total distortion ratio  
+([ITU-T G.726], 32 kbit/s) for "Sinewave" method**
+
+| <b>Receiving level at<br/>the digital interface<br/>(dBm0)</b> | <b>Receiving ratio<br/>(dB)</b> |
+|----------------------------------------------------------------|---------------------------------|
+| -45                                                            | 17.3                            |
+| -40                                                            | 22.3                            |
+| -30                                                            | 29.2                            |
+| -20                                                            | 30.9                            |
+| -10                                                            | 31.2                            |
+| -3                                                             | 29.7                            |
+| 0                                                              | 25.0                            |
+
+##### 5.2.4.2.1 Measurement method
+
+After a correct activation of the system, a digitally simulated sinewave signal at frequencies of 315, 510 and 1020 Hz is applied to the digital interface respectively. The signal level is  $-16 \text{ dBm}0$ , except for the sinewave signal with a frequency of 1020 Hz that shall be applied to the digital interface at the following levels:  $-45, -40, -35, -30, -25, -20, -15, -10, -3, 0 \text{ dBm}0$ .
+
+The total distortion power shall be measured at ERP with A-weighting. The DRP-ERP correction as defined in [ITU-T P.57] is applied. The ratio of the signal-to-total distortion power is calculated.
+
+### 5.2.5 Receiving out-of-band signals
+
+In view of the following considerations:
+
+- compatibility with coder and decoder requirements according to [ITU-T G.712];
+- compatibility with existing practices in the mixed analogue-digital network in use today,
+
+the following limits are recommended:
+
+Any spurious out-of-band image signal above 4.6 kHz and up to 8 kHz measured selectively shall be lower than the in-band acoustic level measured with a reference signal (1000 Hz, sinewave). The minimum level difference between the reference signal level and the out-of-band image signal level shall be as given in Table 16:
+
+**Table 16 – Discrimination levels – Receiving out-of-band signals**
+
+| Image signal frequency | Minimum level difference |
+|------------------------|--------------------------|
+| 4.6 kHz                | 35 dB                    |
+| 8.0 kHz                | 45 dB                    |
+
+NOTE – The limit at intermediate frequencies lies on a straight line drawn between the given values on a log (frequency) – linear (dB) scale.
+
+#### 5.2.5.1 Measurement method
+
+The actual test signals used are a digitally activation signal followed by a digitally simulated sine wave with the frequencies of 500 Hz, 1000 Hz, 2000 Hz and 3150 Hz ( $-16 \text{ dBm}0$ , at the digital reference point or the equivalent analogue point) respectively. The level of spurious out-of-band image signals at frequencies up to 8 kHz are measured selectively at the ear simulator.
+
+The measured spurious out-of-band signals shall be compared to the measured in-band 1000 Hz signal.
+
+NOTE – Depending on the type of codec, the test signal used may need to be adapted.
+
+### 5.2.6 Receiving linearity
+
+Considering that some non-linear techniques may be used in digital telephones, for example:
+
+- automatic gain control;
+- compressor/expander techniques,
+
+these devices may be deliberately designed non-linear over the input level range specified and may have dynamic characteristics (e.g., attack and hangover time). Unless a digital telephone has specifically designed non-linear characteristics, the following limits are recommended.
+
+NOTE – If a digital telephone has specifically designed non-linear characteristics, alternative test methods based on more complex test signals may be needed for these tests. The principles are described in [ITU-T P.501] and [ITU-T P.502].
+
+For digital telephones that are intended to have linear input versus output characteristics, the gain variation relative to the gain at an input level of  $-10$  dBm0, should be within the limits given in Table 17. For intermediate levels, the same limits for gain variation apply.
+
+**Table 17 – Receiving linearity**
+
+| Receiving level<br>at the digital interface<br>(dBm0) | Upper limit<br>(dB) | Lower limit<br>(dB) |
+|-------------------------------------------------------|---------------------|---------------------|
+| +3                                                    | 0.5                 | -0.5                |
+| -40                                                   | 0.5                 | -0.5                |
+| -40                                                   | 1                   | -1                  |
+| -50                                                   | 1                   | -1                  |
+| <-50                                                  | 2                   | -2                  |
+
+#### 5.2.6.1 Measurement method
+
+After a correct activation of the system, a digitally simulated sinewave signal with a frequency in the range 1004 Hz to 1025 Hz shall be applied at the digital interface at the following levels:
+
+$-55, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5, 0, 3$  dBm0.
+
+The variation of gain relative to the gain at an input level of  $-10$  dBm0 shall be measured in the artificial ear. The measured sound pressure level should be transferred from DRP to ERP according to [ITU-T P.57].
+
+NOTE 1 – If the sinewave techniques cannot be used (which is likely if the terminal has a noise reduction device), another appropriate technique should be applied. For example, an artificial speech generator (e.g., as specified in [ITU-T P.50] and [ITU-T P.501]) and a spectrum analyser can be used.
+
+NOTE 2 – Selective measurements may be used to avoid the effects of ambient noise.
+
+## 5.3 Sidetone characteristics
+
+### 5.3.1 Sidetone masking rating (STMR)
+
+In view of the following considerations:
+
+- the optimum STMR for conditions free from echo;
+- the masking effect of sidetone on short delay talker echo,
+
+the value of STMR shall be 10 dB to 20 dB when corrected to nominal values of SLR (8 dB) and RLR (2 dB).
+
+NOTE – For this correction, the formula  $STMR = STMR_m - (SLR_m - 8 + RLR_m - 2)$  should be used. Index m indicates measured values.
+
+Where a user-controlled receiving volume control is provided, the STMR shall be 10 dB to 20 dB for all volume control settings. It is preferable to have a constant STMR independent of the volume control setting.
+
+#### 5.3.1.1 Measurement method
+
+The test signal to be used for the measurements shall be the artificial voice according to [ITU-T P.50]. The spectrum of the acoustic signal produced by the artificial mouth is calibrated under free-field conditions at MRP. The test signal level shall be  $-4.7$  dBPa at MRP. The test signal level is averaged over the complete test signal sequence.
+
+The talker sidetone sensitivity/frequency characteristic is measured according to [ITU-T P.64] using the measurement set-up of Figure 5-5. The reference codec is not used in this measurement but may remain in the test circuit, with no external coupling path.
+
+Sidetone masking rating (STMR) should be calculated from the sensitivity/frequency characteristic determined from above by means of [ITU-T P.79]. The measured sound pressure should be transferred from DRP to ERP.
+
+![Figure 5-5: Measurement of talker sidetone sensitivity/frequency characteristic, HATS position. The diagram shows a measurement setup where a Digital telephone is connected to an Interface, which is connected to a Test bed containing a D/A converter and a 600 Ω load. The Digital telephone is also connected to a Measuring amplifier and a Level recorder. The Measuring amplifier is connected to an Artificial ear, which is connected to a Signal generator. The Artificial ear and Signal generator are connected to a Quiet room. The Digital telephone is connected to the Artificial ear via a Control line. The Test bed is connected to the Interface via a Control line.](a149b400127a3e3e50b3c98d27c5935c_img.jpg)
+
+Figure 5-5: Measurement of talker sidetone sensitivity/frequency characteristic, HATS position. The diagram shows a measurement setup where a Digital telephone is connected to an Interface, which is connected to a Test bed containing a D/A converter and a 600 Ω load. The Digital telephone is also connected to a Measuring amplifier and a Level recorder. The Measuring amplifier is connected to an Artificial ear, which is connected to a Signal generator. The Artificial ear and Signal generator are connected to a Quiet room. The Digital telephone is connected to the Artificial ear via a Control line. The Test bed is connected to the Interface via a Control line.
+
+P.310(09)\_F5.5
+
+**Figure 5-5 – Measurement of talker sidetone sensitivity/frequency characteristic, HATS position**
+
+### 5.3.2 D-factor
+
+In view of the following considerations:
+
+- the difficulties of high ambient noise conditions;
+- what subscribers are used to having with present analogue sets,
+
+the value of D-factor shall not be less than 0 dB. As the long-term objective, the value of +3 dB is recommended.
+
+NOTE 1 – The key parameter for the handset performance in noisy conditions is the D-factor.
+
+NOTE 2 – When a telephone set is connected into the telecom network, there is a firm relation between STMR and LSTR:  $D = LSTR - STMR$ , here LSTR is the listener sidetone loudness rating.
+
+#### 5.3.2.1 Measurement method
+
+The measurement method is defined according to Annex E of [ITU-T P.79].
+
+For linear microphones and circuitry, D-factor is computed directly from measurements of the difference  $\Delta S_m$  between the sending sensitivities for diffuse and direct sound,  $S_{si}$  (diff) and  $S_{si}$  (direct), respectively.
+
+$$\Delta S_m = S_{si} (\text{diff}) - S_{si} (\text{direct})$$
+
+Both  $S_{si}$  (diff) and  $S_{si}$  (direct) can be measured according to clause 5.1.1, using the measurement set-up of Figure 5-6 except that diffuse sound is used as the input signal when measuring  $S_{si}$  (diff). The sound pressure level of the diffuse sound field shall be adjusted in the range of –54 dBPa(A) to –29 dBPa(A) at MRP in the absence of artificial mouth. The actual level and type of noise should always be stated in quoting test results.
+
+$D$  is computed as a weighted average of  $\Delta S_m$ ,
+
+$$D = -\sum_{i=1}^N K_i \cdot \Delta S_m$$
+
+The coefficients  $K_i$  are given in Table E.1 of [ITU-T P.79].
+
+NOTE – For sets with non-linear microphones and/or non-linear circuitry,  $D$  depends on the room noise level.
+
+![Figure 5-6: Measurement of listener sidetone sensitivity/frequency characteristic, HATS position. The diagram shows a measurement setup. A 'Digital telephone' is connected to an 'Artificial mouth' and an 'Artificial ear'. The 'Artificial ear' is connected to a 'Measuring amplifier', which is connected to 'Channel 2' of a 'Spectrum analyser'. The 'Digital telephone' is connected to an 'Interface', which is connected to a 'Computer' and a 'Plotter'. The 'Computer' is also connected to 'Channel 1' of the 'Spectrum analyser'. The 'Interface' is connected to a 'Test bed' containing a 'D/A' converter, which is connected to a '600 Ω' load. A 'Control' signal is also connected to the 'Interface'. The 'Artificial mouth', 'Artificial ear', and 'Digital telephone' are enclosed in a dashed box labeled 'Diffuse sound field'. The diagram is labeled 'P.310(09)_F5.6'.](b235edb1dbe659e2782c9a0e47775ca4_img.jpg)
+
+Figure 5-6: Measurement of listener sidetone sensitivity/frequency characteristic, HATS position. The diagram shows a measurement setup. A 'Digital telephone' is connected to an 'Artificial mouth' and an 'Artificial ear'. The 'Artificial ear' is connected to a 'Measuring amplifier', which is connected to 'Channel 2' of a 'Spectrum analyser'. The 'Digital telephone' is connected to an 'Interface', which is connected to a 'Computer' and a 'Plotter'. The 'Computer' is also connected to 'Channel 1' of the 'Spectrum analyser'. The 'Interface' is connected to a 'Test bed' containing a 'D/A' converter, which is connected to a '600 Ω' load. A 'Control' signal is also connected to the 'Interface'. The 'Artificial mouth', 'Artificial ear', and 'Digital telephone' are enclosed in a dashed box labeled 'Diffuse sound field'. The diagram is labeled 'P.310(09)\_F5.6'.
+
+**Figure 5-6 – Measurement of listener sidetone sensitivity/frequency characteristic, HATS position**
+
+## 5.4 Echo path loss characteristics
+
+### 5.4.1 Weighted terminal coupling loss (TCL<sub>w</sub>)
+
+In view of the following considerations:
+
+- the aim to achieve as high an acoustic coupling loss as possible to minimize degradation caused by echo;
+- that the far-end talker echo should be controlled under all volume control settings, and for the range of transducers sensitivities as long as the handset is properly used;
+- the far-end terminal may be connected via a mobile or an IP network which introduces long talker echo path delay;
+- what is practically obtainable in real use where the customer himself chooses the way to hold his handset,
+
+the following limit is recommended:
+
+In order to meet the ITU-T G.131 talker echo objective requirements, the weighted terminal coupling loss (TCL<sub>w</sub>) should be greater than 45 dB when measured under free-field conditions and with SLR normalized to SLR = +8 dB and RLR = +2 dB. For example, if the measured TCL<sub>w</sub> is 48 dB, the measured SLR is +9 dB and the measured RLR is +3 dB, then the normalized value of TCL<sub>w</sub> = 48 dB + (8 – 9) dB + (2 – 3) dB = 46 dB.
+
+For handsets fitted with a volume control, the TCL<sub>w</sub> shall be not less than 40 dB for the higher gain settings above the nominal setting of the volume control. Permanently increasing SLR as the RLR is decreased when increasing the receive volume level is not recommended.
+
+NOTE – In consideration of the increasing delays introduced by modern networks, a higher TCL<sub>w</sub> value than that specified here may be necessary for proper operation with these networks.
+
+#### 5.4.1.1 Measurement method
+
+Terminal coupling loss (TCL) is measured in such a way that the inherent mechanical coupling of the handset is not affected.
+
+When performing tests, the test space acoustics must not have a dominating influence. The test should be performed in the environment as defined in clause 4.4.
+
+The test is performed with the handset mounted at HATS position according to [ITU-T P.64].
+
+The test signal may be a composite source signal (CSS) as defined in [ITU-T P.501] with a length of 4096 points (for the 48 kHz sampling rate) and a crest factor of 6 dB. The low crest factor is achieved by random alternation of the phase between  $-180^\circ$  and  $180^\circ$ . The length of the complete test signal composed of at least four sequences of CSS shall be at least one second. The test signal level is  $-3$  dBm0. The calibration shall be determined during the ON portions of the signal. The test signal shall be band-limited to 100 Hz  $\sim$  4000 Hz. A logarithmically distributed multi-sinewave is equally well applicable with G.711 codecs.
+
+For non-linear and/or time variant systems, it must be ensured that the equipment under test is under "steady state conditions". Depending on the task, e.g., echo cancellers should be fully converged. This can be achieved by invoking the test signal for at least 2 seconds before the actual measurement occurs.
+
+The attenuation from digital input to digital output is measured at one-twelfth octave frequencies as given by the R.40-series of preferred numbers in [ISO 3] for frequencies from 300 to 3350 Hz, using the measurement arrangement shown in Figure 5-7.
+
+The TCLw is calculated according to clause B.4 of [ITU-T G.122] (trapezoidal rule).
+
+NOTE 1 – The echo impairment perceived by the person at the opposite end of the connection from a telephone set is a function of the magnitude of the talker echo signal as well as the talker echo path delay. The echo signal becomes more disturbing as the talker echo path delay increases. Thus, a telephone set with adequate TCLw performance on low delay connections may provide satisfactory performance while the same may not be true for connections that have a long delay.
+
+NOTE 2 – There might be problems measuring 46 dB TCL in the case where sophisticated coding with limited dynamic range is used. In such cases, typically speech or speech-like test signals need to be used that themselves have crest factors in the range of 15 dB, which reduces the measurement dynamic by the same amount. In such cases, the signal measured in the sending direction should be evaluated more carefully in order to find whether an echo signal is present, or whether this signal is completely masked by the noise signal introduced by the codec. If the signal measured in the sending direction is completely masked by the noise, the requirement can be considered to be fulfilled. If this is not the case, more sophisticated measurement procedures such as time averaging (in order to improve the signal-to-noise ratio) need to be applied in order to achieve reliable measurement results.
+
+![Figure 5-7: Measurement of terminal coupling loss, HATS position. The diagram shows a 'Digital telephone set' connected to an 'Interface'. A 'Control' signal is input to the Interface. The Interface is connected to a 'Test bed' (dashed box). Inside the Test bed, there are two parallel paths: one with a 'D/A' converter followed by a '600 Ω' resistor, and another with an 'A/D' converter followed by a '600 Ω' resistor. The output of the D/A path is labeled 'V_out' and the output of the A/D path is labeled 'V_in'. A microphone icon is shown next to the Digital telephone set. The label 'P.310(09)_F5.7' is at the bottom left.](f0a97d0d3818a253c1d2a009966081b1_img.jpg)
+
+Figure 5-7: Measurement of terminal coupling loss, HATS position. The diagram shows a 'Digital telephone set' connected to an 'Interface'. A 'Control' signal is input to the Interface. The Interface is connected to a 'Test bed' (dashed box). Inside the Test bed, there are two parallel paths: one with a 'D/A' converter followed by a '600 Ω' resistor, and another with an 'A/D' converter followed by a '600 Ω' resistor. The output of the D/A path is labeled 'V\_out' and the output of the A/D path is labeled 'V\_in'. A microphone icon is shown next to the Digital telephone set. The label 'P.310(09)\_F5.7' is at the bottom left.
+
+**Figure 5-7 – Measurement of terminal coupling loss, HATS position**
+
+### 5.4.2 Stability loss
+
+In view of the following considerations:
+
+- the aim to achieve a good stability;
+- what is practically obtainable with normal type of handsets and transducers,
+
+the following limit is recommended:
+
+With the handset lying on and the transducers facing a hard surface, the attenuation from the digital input to the digital output shall be preferably at least 10 dB but not less than 6 dB at all frequencies in the range of 200 Hz to 4 kHz with SLR + RLR normalized to OLR = +10 dB.
+
+NOTE – Those handsets that are fitted with a volume control should maintain stability throughout the volume control range.
+
+#### 5.4.2.1 Measurement method
+
+The signal used in stability measurement is the same with TCLw, with a different input signal level of 0 dBm0.
+
+The measurement is made at one-twelfth octave intervals for frequencies from 200 Hz to 4000 Hz. With the handset and the transmission circuit fully active, the attenuation from digital input to digital output is measured under one of the following conditions. Stability is the least value of the attenuation in the band 200 to 4000 Hz.
+
+##### Method 1
+
+- a) The handset shall be positioned on one inside surface at the corner formed by the intersection of three perpendicular, smooth, hard surfaces. Each surface shall extend 0.5 m from the vertex of the corner. One surface shall be marked with a diagonal line extending from the corner and a reference position 250 mm from the corner formed by the three surfaces, as shown in Figure 5-8.
+- b) The handset, with the transmission circuit fully active, shall be positioned on the defined surface as follows:
+  - i) the mouthpiece and ear-cap shall face towards the surface;
+  - ii) the handset shall be placed centrally on the diagonal line with the ear-cap nearest to the apex of the corner;
+  - iii) the extremity of the handset shall coincide with the normal to the reference point, as shown in Figure 5-8.
+
+![Figure 5-8: Reference corner and reference position. The diagram shows a 3D corner formed by three perpendicular surfaces. A diagonal line is drawn on the bottom surface from the corner vertex. A reference point is marked on this diagonal line at a distance of 250 mm from the corner. Below the 3D diagram, a 2D side view shows a handset positioned on the diagonal line, with its ear-cap facing the corner and its mouthpiece facing away. The distance from the corner to the reference point is labeled 250. The text 'P.310(09)_F5.8' is visible in the 3D diagram.](27a0ba79d8b4a7d9d9380ca6a3229f1a_img.jpg)
+
+The diagram illustrates the setup for Method 1. It features a 3D perspective view of a corner where three surfaces meet. A diagonal line is marked on the bottom surface, starting from the corner vertex. A reference point is indicated on this line at a distance of 250 mm from the corner. Below this, a 2D side view shows a handset placed on the diagonal line. The handset's ear-cap is positioned closest to the corner, and its mouthpiece is further away. A dimension line indicates the 250 mm distance from the corner to the reference point. The label 'P.310(09)\_F5.8' is present in the 3D diagram.
+
+Figure 5-8: Reference corner and reference position. The diagram shows a 3D corner formed by three perpendicular surfaces. A diagonal line is drawn on the bottom surface from the corner vertex. A reference point is marked on this diagonal line at a distance of 250 mm from the corner. Below the 3D diagram, a 2D side view shows a handset positioned on the diagonal line, with its ear-cap facing the corner and its mouthpiece facing away. The distance from the corner to the reference point is labeled 250. The text 'P.310(09)\_F5.8' is visible in the 3D diagram.
+
+Figure 5-8 – Reference corner and reference position
+
+##### Method 2
+
+The handset, with the transmission circuit fully active, is placed with the ear-cap and mouthpiece facing a hard, smooth surface free of any other object for 0.5 m.
+
+## 5.5 Delay
+
+Delay is a complex end-to-end issue. Certain aspects of delay can be optimized in digital terminals, such as the internal hardware/firmware delay. Other aspects are also important sources of delay, but they are a function of the selected codec, so they cannot be optimized in digital terminals.
+
+Considering the delay, referred to in this Recommendation,
+
+- the coding, decoding and filtering according to [ITU-T G.712] and [ITU-T G.726], as appropriate;
+- the air paths and transducers involved,
+
+the following is recommended:
+
+The sum of the delays from MRP to the digital interface (sending direction), and from the digital interface to the artificial ear (receiving direction), shall not exceed 25 ms for digital telephones using G.711 encoding, and 30 ms for G.726 encoding.
+
+### 5.5.1 Measurement method
+
+#### 5.5.1.1 Sending delay measurement
+
+The test signal to be used for the measurements shall be a composite source signal (CSS) as described in [ITU-T P.501]. The handset terminal is set-up as described in clause 4.3. The delay is calculated using the cross-correlation function between the signal at the electrical test point and the signal at MRP. The measurement is corrected by the delay introduced by the test equipment. The delay is expressed in ms, determined from the maximum of the cross-correlation function.
+
+#### 5.5.1.2 Receiving delay measurement
+
+The test signal to be used for the measurements shall be a composite source signal (CSS) as described in [ITU-T P.501]. The handset terminal is set-up as described in clause 4.3. The delay is calculated using the cross-correlation function between the signal at the electrical test point and the signal arriving at the artificial ear. The measurement is corrected by the delay introduced by the test equipment. The delay is expressed in ms, determined from the maximum of the cross-correlation function.
+
+# 6 Headset technical requirements
+
+Most headset technical requirements are the same as those of the handset terminal. To condense contents and avoid redundancy, this clause only covers those which are particular to headsets.
+
+The headset should be mounted at the test position using a HATS as specified in [ITU-T P.380]. For binaural headsets, the following applies:
+
+- For headsets that do not have left and right ear wearing indication, they can be tested on a HATS that is equipped with one functional ear simulator. The primary receiver (where the microphone system is located) should be positioned on the functional ear simulator for all tests. The secondary receiver shall be moved into position for evaluating frequency response, RLR and distortion measurements.
+- For headsets that are designed to be worn in only one manner or fashion, a HATS with two functional ear simulators shall be used. The two receivers shall be tested separately. The secondary receiver need only be tested for frequency response, RLR and distortion.
+
+## 6.1 Sending characteristics
+
+Refer to clause 4.3 for headset measurement set-up. Refer to clause 5 for sending requirements and measurements.
+
+## 6.2 Receiving characteristics
+
+### 6.2.1 Receiving loudness rating (RLR)
+
+- the nominal value of RLR shall be +2 dB, with a tolerance of  $\pm 3$  dB;
+- for binaural earphones, the nominal value of RLR shall be 8 dB for each earphone, with a tolerance of  $\pm 3$  dB.
+
+#### 6.2.1.1 Measurement method
+
+This should be calculated from the sensitivity/frequency characteristic determined in clause 5.1.1.1 by means of [ITU-T P.79]. The DRP-ERP correction, as defined in [ITU-T P.57], is applied.
+
+NOTE – Other methods for calculating loudness rating used by some Administrations for their own internal planning purposes can be found in [b-Teleph].
+
+### 6.2.2 Receiving noise
+
+When driven by a signal corresponding to a decoder value quiet code, the maximum acoustic noise level at ERP shall be as follows:
+
+- if no user-controlled volume control is provided or when the volume control is set to nominal RLR value, the measured receiving noise at ERP shall not be greater than  $-57$  dBPa(A);
+
+For binaural headsets, each earphone shall not exceed  $-60$  dBPa(A).
+
+- if a volume control is provided, the measured receiving noise at ERP shall not be greater than  $-54$  dBPa(A) at the maximum setting of the volume control;
+
+For binaural headsets, each earphone shall not exceed  $-57$  dBPa(A).
+
+- no peaks in any 1/3-octave band with the level of 10 dB higher than the average noise spectrum in the frequency domain shall occur.
+
+#### 6.2.2.1 Measurement method
+
+The receiving noise shall be measured in a quiet environment as defined in clause 4.4.
+
+The receiving noise level at ERP is measured with A-weighting. The DRP-ERP correction as defined in [ITU-T P.57] is applied.
+
+## 6.3 Echo path loss characteristics
+
+### 6.3.1 Stability loss
+
+With the headset positioned on the defined surface as specified in clause 5.4.2.1, the attenuation from the digital input to the digital output shall be preferably at least 10 dB but not less than 6 dB at all frequencies in the range of 200 Hz to 4 kHz with SLR + RLR normalized to OLR = +10 dB.
+
+NOTE – Those handsets that are fitted with a volume control should maintain stability throughout the volume control range.
+
+#### 6.3.1.1 Measurement method
+
+The signal used in stability measurement is the same with TCLw, with a different input signal level of 0 dBm0.
+
+The measurement is made at one-twelfth octave intervals for frequencies from 200 Hz to 4000 Hz. With the headset and the transmission circuit fully active, the attenuation from digital input to digital output is measured under one of the following conditions. Stability is the least value of the attenuation in the band 200 to 4000 Hz.
+
+The headset, with the transmission circuit fully active, shall be positioned on the defined surface as follows:
+
+- the microphone and the receiver shall face towards the surface;
+- the headset receiver shall be placed centrally at the reference point as shown in Figure 5-8;
+- the headset microphone is positioned as close as possible to the receiver.
+
+# Annex A
+
+## Distortion allowances
+
+(This annex forms an integral part of this Recommendation)
+
+In producing the distortion characteristics at sending and receiving allowances for non-linear products, the following ways have been accounted for:
+
+- The transducers (microphone and earphone) have a 1% distortion allowance for most input levels. The exceptions are the highest and lowest input levels which have been allowed 5% and the second lowest to have 2%.
+- Noise levels for sending and receiving are equivalent to  $-64$  dBm0p.
+
+The total contribution of these factors is calculated using power summation.
+
+NOTE 1 – This is of particular interest for developing specifications for other types of "Waveform" codecs not covered in this Recommendation.
+
+NOTE 2 – It may be prudent to allow 0.2-0.4 dB to the final calculation to account for other sources of non-linearity, e.g., artificial mouth, amplifiers.
+
+NOTE 3 – Room noise at  $\leq -64$  dBPa(A) has no significant effect.
+
+# Bibliography
+
+- [b-Teleph] ITU-T Handbook on Telephonometry (1992), *Measurement Method: Telephonometry*.
+
+
+
+
+
+# **SERIES OF ITU-T RECOMMENDATIONS**
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| Series G        | Transmission systems and media, digital systems and networks                                |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K        | Protection against interference                                                             |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| <b>Series P</b> | <b>Terminals and subjective and objective assessment methods</b>                            |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

marked/P/T-REC-P.370-199608-I_PDF-E/raw.md

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+
+
+![ITU logo: A globe with a lightning bolt and the letters ITU.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: A globe with a lightning bolt and the letters ITU.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.370**
+
+(08/96)
+
+SERIES P: TELEPHONE TRANSMISSION QUALITY
+
+Subscribers' lines and sets
+
+# --- **Coupling Hearing Aids to Telephone sets**
+
+ITU-T Recommendation P.370
+
+(Previously "CCITT Recommendation")
+
+---
+
+# ITU-T P-SERIES RECOMMENDATIONS **TELEPHONE TRANSMISSION QUALITY**
+
+|                                                                                               |                    |
+|-----------------------------------------------------------------------------------------------|--------------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality | P.10-P.29          |
+| <b>Subscribers' lines and sets</b>                                                            | <b>P.300-P.399</b> |
+| Subscribers' lines and sets                                                                   | P.30-P.39          |
+| Transmission standards                                                                        | P.40-P.49          |
+| Objective measuring apparatus                                                                 | P.500-P.599        |
+| Objective measuring apparatus                                                                 | P.50-P.59          |
+| Objective electro-acoustical measurements                                                     | P.60-P.69          |
+| Measurements related to speech loudness                                                       | P.70-P.79          |
+| Methods for objective and subjective assessment of quality                                    | P.800-P.999        |
+| Methods for objective and subjective assessment of quality                                    | P.80-P.99          |
+
+*For further details, please refer to ITU-T List of Recommendations.*
+
+# FOREWORD
+
+The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
+
+The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993).
+
+ITU-T Recommendation P.370, was prepared by ITU-T Study Group 12 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 30th of August 1996.
+
+---
+
+# NOTE
+
+In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+© ITU 1997
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+# CONTENTS
+
+*Page*
+
+|       |                                                                                                                         |    |
+|-------|-------------------------------------------------------------------------------------------------------------------------|----|
+| 1     | Scope .....                                                                                                             | 1  |
+| 2     | Normative references .....                                                                                              | 1  |
+| 3     | Definitions and abbreviations.....                                                                                      | 2  |
+| 3.1   | Definitions .....                                                                                                       | 2  |
+| 3.2   | Abbreviations.....                                                                                                      | 2  |
+| 4     | Magnetic field strength around the earcap of telephone handsets which provide for coupling to hearing aids .....        | 2  |
+| 4.1   | Introduction .....                                                                                                      | 2  |
+| 4.2   | Magnetic field strength measurements and recommended values .....                                                       | 3  |
+| 4.2.1 | Calibration of acoustic receive level .....                                                                             | 3  |
+| 4.2.2 | Magnetic field strength level.....                                                                                      | 4  |
+| 4.2.3 | Linearity of the magnetic field strength .....                                                                          | 4  |
+| 4.2.4 | Measurement of frequency characteristics.....                                                                           | 4  |
+| 4.3   | Probe coil.....                                                                                                         | 5  |
+| 4.3.1 | Dimensions .....                                                                                                        | 5  |
+| 4.3.2 | Calibration of the probe coil .....                                                                                     | 5  |
+| 4.3.3 | Distortion .....                                                                                                        | 5  |
+| 5     | Characteristics of telephone sets that provide additional amplification for the benefit of hearing impaired users ..... | 6  |
+| 5.1   | Introduction .....                                                                                                      | 6  |
+| 5.2   | Sending characteristics .....                                                                                           | 6  |
+| 5.2.1 | Sensitivity .....                                                                                                       | 6  |
+| 5.2.2 | Frequency response.....                                                                                                 | 6  |
+| 5.3   | Receiving characteristics .....                                                                                         | 7  |
+| 5.3.1 | Sensitivity .....                                                                                                       | 7  |
+| 5.3.2 | Frequency response.....                                                                                                 | 7  |
+| 5.3.3 | Restoring normal receive amplification.....                                                                             | 7  |
+| 5.4   | Sidetone .....                                                                                                          | 7  |
+| 6     | Electrical coupling of telephone sets to hearing aids .....                                                             | 8  |
+| 6.1   | Introduction .....                                                                                                      | 8  |
+| 6.2   | Electrical characteristics .....                                                                                        | 8  |
+| 6.2.1 | Point of connection in the telephone set .....                                                                          | 8  |
+| 6.2.2 | Electrical characteristics at interconnection point.....                                                                | 8  |
+| 6.3   | Interconnection with the telephone set .....                                                                            | 9  |
+| 6.3.1 | Connector type.....                                                                                                     | 9  |
+| 6.3.2 | Connector position.....                                                                                                 | 9  |
+| 6.4   | Safety issues.....                                                                                                      | 9  |
+|       | Annex A – Measurement of an acousto-magnetic adapter generating a magnetic field.....                                   | 10 |
+| A.1   | Measurement procedures .....                                                                                            | 10 |
+| A.2   | Magnetic field requirements .....                                                                                       | 10 |
+| A.3   | Physical properties.....                                                                                                | 10 |
+|       | Appendix I – Examples of frequency characteristics of hearing aids coupled to telephones.....                           | 10 |
+|       | Appendix II – Bibliography.....                                                                                         | 15 |
+
+# SUMMARY
+
+This Recommendation has been updated from Recommendation P.37, Coupling Hearing Aids to Telephone sets.
+
+Clause 4 covers inductive coupling and is technically similar to the original Recommendation P.37. Clause 4 however now includes the relevant figures that were previously referred out to other Recommendations. It presents recommended levels and frequency characteristics for the inductive field at the telephone earphone relative to a sound level presented at the same earphone.
+
+Clause 5 covers additional amplification that may be provided for the benefit of hearing impaired users, and only editorial changes have been made to the text originally contained in Recommendation P.37. Limits for the additional amplification and range of volume control are given. Frequency response is also covered.
+
+Clause 6 introduces the possibility of electrical coupling of a telephone set to a hearing aid. It is compatible with IEC Publication 118 Part 6, which covers the characteristics of hearing aid electrical input circuits. The electrical output level relative to the sound level in the same telephone's earphone is given in this Recommendation, together with frequency response, source impedance and maximum output level.
+
+Technically this Recommendation is compatible with similar documents recently drafted within ETSI covering the same subjects.
+
+# FOREWORD
+
+It is recognized that there is a sizeable proportion of telephone users that have difficulty in conversing over a telephone connection due to hearing loss. To alleviate these difficulties special means have been provided in many national systems to enable hearing impaired users to couple their hearing aids inductively to the telephone receiver, and a number of national/international specifications define characteristics for this form of coupling. Clause 4 addresses the requirements for successful inductive coupling of hearing aids to telephone sets.
+
+Furthermore, it is also recognized that many hearing impaired users are able to have satisfactory telephone conversations while coupling their hearing aids acoustically to the telephone receiver, or even using the telephone handset without a hearing aid. This latter situation is possible due to the fact that under good conditions a telephone connection can be louder than a face-to-face conversation over a one-metre air path by up to 30 dB. Provision of additional amplification in the mouth-to-ear path can greatly increase the proportion of telephone conversations involving hearing impaired users that are rated “good”. Clause 5 addresses this form of coupling.
+
+Certain national standards also exist to enable direct electrical connection of hearing aids to telephone apparatus. This form of coupling is addressed in clause 6, and has been written to be compatible with the IEC Publication 118-6, 1984, covering the characteristics of electrical input circuits for hearing aids.
+
+## NOTES
+
+1 Care should be taken when designing hearing aids to include sufficient immunity to radio frequency interference to avoid disturbances arising from the detection of radio signals emitted by cordless and mobile telephones.
+
+2 Tests have shown that telephone earphones having low acoustic impedance, which exhibit less low frequency loss due to leakage effects, couple acoustically very well into hearing aids by presenting a much flatter overall frequency characteristic to the ear of the user than conventional earphones having high acoustic impedance.
+
+# COUPLING HEARING AIDS TO TELEPHONE SETS
+
+(Geneva, 1996)
+
+# 1 Scope
+
+Clause 4 applies to telephone handsets having supra-aural earphones that can be connected to the Public Switched Telephone Network (PSTN) or the Integrated Services Digital Network (ISDN) which are intended for direct application to the ear (e.g. traditional handsets, operators' headsets) and which provide a magnetic field for coupling to hearing aids. It specifies the level, linearity and frequency dependence of the magnetic field strength produced by the handset and characteristics for the calibrated probe coil.
+
+Clause 5 specifies the electro-acoustic performance characteristics of telephony terminals which are intended for direct application to the ear (e.g. traditional handsets, operators' headsets) and which provide, at the earphone, additional amplification in the receiving direction compared with the Receiving Loudness Rating (RLR) specified in the requirements of the national system.
+
+Clause 6 specifies the electrical characteristics for the electrical coupling of the telephony function, implemented telecommunication terminal equipment, to hearing aids. It specifies the level and frequency response relative to the acoustic output at the earphone, also the noise and maximum level.
+
+Annex A specifies the measuring method for an acousto-magnetic adapter that converts the acoustic output of an associated telephone receiver to a magnetic field, in accordance with 4.2.1 and 4.2.2, that can be received by the magnetic pick-up coil in a hearing aid.
+
+# 2 Normative references
+
+The following Recommendations, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published.
+
+- IEC Publication 118-6: 1984, *Hearing aids – Part 6: Characteristics of electrical input circuits for hearing aids*.
+- ITU-T Recommendation P.10 (1993), *Vocabulary of terms on telephone transmission quality and telephone sets*.
+- IEC Publication 118-4: 1981, *Hearing aids – Part 4: Magnetic field strength in audio-frequency induction loops for hearing aid purposes*.
+- IEC Publication 118-1: 1995, *Hearing aids – Part 1: Hearing aids with induction pick-up coil input*.
+- ITU-T Recommendation P.340 (1996), *Transmission characteristics of hands-free telephones*.
+- ITU-T Recommendation G.121 (1993), *Loudness Ratings (LRs) of national systems*.
+- IEC Publication 130-8: 1976, *Connectors for frequencies below 3 MHz – Part 8: Concentric connectors for audio circuits in radio receivers*.
+- IEC Publication 268-11: 1987, *Sound system equipment – Part 11: Application of connectors for the interconnection of sound system equipment*.
+- ITU-T Recommendation P.57 (1993), *Artificial ears*.
+- CCITT Recommendation P.48 (1988), *Specification for an intermediate reference system*.
+
+<sup>1)</sup> Previously Recommendation P.37.
+
+# 3 Definitions and abbreviations
+
+## 3.1 Definitions
+
+The relevant definitions given in Recommendation P.10 apply along with the following:
+
+**3.1.1 level of magnetic field strength:** the maximum level of the magnetic field strength and its measurement are given in 4.2.2. The units are amperes per metre (A/m).
+
+**3.1.2 plane of measurement:** A plane parallel to the earcap at a distance of 10 mm.
+
+**3.1.3 The adapter plane:** It is defined as the plane formed by the contacting points of a flat surface against the surface of the acousto-magnetic adapter opposite the earcap connection.
+
+## 3.2 Abbreviations
+
+For the purposes of this Recommendation, the following abbreviations are used.
+
+|       |                                           |
+|-------|-------------------------------------------|
+| AGC   | Automatic Gain Control                    |
+| DRP   | Drum Reference Point                      |
+| ERP   | Ear Reference Point                       |
+| HATS  | Head and Torso Simulator                  |
+| IEC   | International Electrotechnical Commission |
+| IRS   | Intermediate Reference System             |
+| ISDN  | Integrated Services Digital Network       |
+| LSTR  | Listener Sidetone Rating                  |
+| OLR   | Overall Loudness Rating                   |
+| $p_e$ | Sound pressure level at the ERP           |
+| PSTN  | Public Switched Telephone Network         |
+| RLR   | Receiving Loudness Rating                 |
+| SLR   | Sending Loudness Rating                   |
+| STMR  | Sidetone Masking Rating                   |
+| TCL   | Terminal Coupling Loss                    |
+
+# 4 Magnetic field strength around the earcap of telephone handsets which provide for coupling to hearing aids
+
+## 4.1 Introduction
+
+Magnetic induction systems incorporated in telephone handsets generate an alternating magnetic field with spatial characteristics which make the field detectable by hearing aids equipped with induction pick-up coils.
+
+Reception of an audio-frequency signal via an induction pick-up coil can often allow an acceptable signal-to-noise ratio to be achieved in cases where the acoustical reception would otherwise be degraded by background noise.
+
+The magnetic field strength which enables induction pick-up coils in hearing aids to function effectively must be high enough to produce an acceptable signal-to-noise ratio but not so high as to cause overloading of the hearing aid.
+
+The value of the magnetic field strength recommended in this Recommendation has been chosen so that these requirements are met as far as possible. (See Bibliography [1] for a discussion on end-to-end levels that can be expected for hearing aid users coupled inductively to a telephone set. This can be compared with the preferred listening levels for users having normal hearing [2]).
+
+Information on the measurement of an acoustic-magnetic adapter generating a magnetic field is found in Annex A.
+
+## 4.2 Magnetic field strength measurements and recommended values
+
+### 4.2.1 Calibration of acoustic receive level
+
+Using the measurement configuration shown in Figure 1 for analogue telephones, Figure 2 for digital telephones, the drive level of the oscillator shall be adjusted to produce a sound pressure level of  $-14$  dBPa (80 dBSPL) at 1000 Hz. This drive level shall be used for determining the level and frequency characteristics of the magnetic field strength.
+
+![Figure 1/P.370: Setting the sound pressure level p_e in the artificial ear for an analogue telephone set. The diagram shows a 'Local telephone system' consisting of a 'Handset', 'Speech Circuit', 'Feed Circuit', and 'Signal Generator (600 ohm source)'. The 'Signal Generator' is connected to the 'Feed Circuit', which is connected to the 'Speech Circuit', which is connected to the 'Handset'. The 'Handset' is connected to an 'Art. Ear' (Artificial Ear). The 'Art. Ear' is connected to a 'Measuring amplifier', which is connected to a 'Voltage measuring device (e.g. voltmeter or signal analyser) calibrated to read sound pressure'. The 'Art. Ear' is also labeled with 'p_e = -14 dBPa'. The diagram is labeled 'T1207710-95/d01'.](367926125450c2bc3f4bdca9d59a62ba_img.jpg)
+
+Figure 1/P.370: Setting the sound pressure level p\_e in the artificial ear for an analogue telephone set. The diagram shows a 'Local telephone system' consisting of a 'Handset', 'Speech Circuit', 'Feed Circuit', and 'Signal Generator (600 ohm source)'. The 'Signal Generator' is connected to the 'Feed Circuit', which is connected to the 'Speech Circuit', which is connected to the 'Handset'. The 'Handset' is connected to an 'Art. Ear' (Artificial Ear). The 'Art. Ear' is connected to a 'Measuring amplifier', which is connected to a 'Voltage measuring device (e.g. voltmeter or signal analyser) calibrated to read sound pressure'. The 'Art. Ear' is also labeled with 'p\_e = -14 dBPa'. The diagram is labeled 'T1207710-95/d01'.
+
+FIGURE 1/P.370
+
+Setting the sound pressure level  $p_e$  in the artificial ear for an analogue telephone set
+
+![Figure 2/P.370: Setting the sound pressure level p_e in the artificial ear for a digital telephone set. The diagram shows a 'Digital Telephone' connected to an 'Interface', which is connected to a 'D/A Conversion Generator', which is connected to a 'Signal Generator'. The 'Signal Generator' is also connected to a 'Control'. The 'Digital Telephone' is connected to a 'Handset', which is connected to an 'Art. Ear' (Artificial Ear). The 'Art. Ear' is connected to a 'Measuring amplifier', which is connected to a 'Voltage measuring device (e.g. voltmeter or signal analyser) calibrated to read sound pressure'. The 'Art. Ear' is also labeled with 'p_e = -14 dBPa'. The diagram is labeled 'T1207720-95/d02'.](a234352dfaccdc24745c88eef7724cc6_img.jpg)
+
+Figure 2/P.370: Setting the sound pressure level p\_e in the artificial ear for a digital telephone set. The diagram shows a 'Digital Telephone' connected to an 'Interface', which is connected to a 'D/A Conversion Generator', which is connected to a 'Signal Generator'. The 'Signal Generator' is also connected to a 'Control'. The 'Digital Telephone' is connected to a 'Handset', which is connected to an 'Art. Ear' (Artificial Ear). The 'Art. Ear' is connected to a 'Measuring amplifier', which is connected to a 'Voltage measuring device (e.g. voltmeter or signal analyser) calibrated to read sound pressure'. The 'Art. Ear' is also labeled with 'p\_e = -14 dBPa'. The diagram is labeled 'T1207720-95/d02'.
+
+FIGURE 2/P.370
+
+Setting the sound pressure level  $p_e$  in the artificial ear for a digital telephone set
+
+### 4.2.2 Magnetic field strength level
+
+Place the centre of the calibrated probe coil (see 4.3) in the plane of measurement and orientate it in any direction for maximum coupling. Determine the magnetic field strength at 1000 Hz using the drive level as given in 4.2.1.
+
+Recommended range of values for the magnetic field strength is:
+
+$$-17 \text{ to } -30 \text{ dB relative to } 1 \text{ A/m.}$$
+
+NOTE – For effective performance, hearing aids with magnetic pick-up coils primarily intended for coupling to magnetic loops in auditoria in accordance with IEC Publication 118-4 are likely to require a field strength in the upper end of the range, i.e.  $-17$  to  $-25$  dB relative to  $1 \text{ A/m}$ .
+
+### 4.2.3 Linearity of the magnetic field strength
+
+With the probe coil positioned as in 4.2.2, increase the 1000 Hz drive level specified in 4.2.1 by 20 dB and measure the resulting magnetic field strength.
+
+The field strength should increase by  $20 \text{ dB} \pm 1 \text{ dB}$ .
+
+### 4.2.4 Measurement of frequency characteristics
+
+With probe coil positioned as in 4.2.2, and the 1000 Hz drive level specified in 4.2.1, vary the frequency from 300 Hz to 5000 Hz for analogue telephones and to the upper frequency limit for digital telephones (4000 or 7000 Hz) as appropriate and measure the resulting field strength. The magnetic field strength frequency characteristics shall fit within the template shown in Figure 3.
+
+![Figure 3/P.370: Magnetic field strength characteristics. A graph showing the magnetic field strength (dB relative to level at 1000 Hz) versus frequency (Hz). The y-axis ranges from -20 to 20 dB, with major ticks at -20, -10, -3, 0, 3, 10, and 20. The x-axis ranges from 300 to 7000 Hz, with major ticks at 300, 500, 1000, 2000, 3400, 5000, and 7000. The graph features two solid lines representing the acceptable range and two dotted lines representing the preferred range. The upper solid line starts at 10 dB at 300 Hz, decreases to 3 dB at 1000 Hz, and then increases to 7 dB at 7000 Hz. The lower solid line starts at -10 dB at 300 Hz, increases to -3 dB at 500 Hz, remains at -3 dB until 1000 Hz, and then decreases to -18 dB at 7000 Hz. The preferred range is indicated by dotted lines at ±3 dB from the 0 dB reference line between 500 Hz and 3400 Hz.](58de972a8c79c238b69cbeeafcc8d5fb_img.jpg)
+
+| Frequency (Hz) | Upper Solid Line (dB) | Lower Solid Line (dB) | Upper Dotted Line (dB) | Lower Dotted Line (dB) |
+|----------------|-----------------------|-----------------------|------------------------|------------------------|
+| 300            | 10                    | -10                   | -                      | -                      |
+| 500            | 5                     | -3                    | -                      | -                      |
+| 1000           | 3                     | -3                    | 3                      | -3                     |
+| 2000           | 4                     | -9                    | 3                      | -3                     |
+| 3400           | 5                     | -18                   | 3                      | -3                     |
+| 5000           | 6                     | -                     | -                      | -                      |
+| 7000           | 7                     | -                     | -                      | -                      |
+
+Figure 3/P.370: Magnetic field strength characteristics. A graph showing the magnetic field strength (dB relative to level at 1000 Hz) versus frequency (Hz). The y-axis ranges from -20 to 20 dB, with major ticks at -20, -10, -3, 0, 3, 10, and 20. The x-axis ranges from 300 to 7000 Hz, with major ticks at 300, 500, 1000, 2000, 3400, 5000, and 7000. The graph features two solid lines representing the acceptable range and two dotted lines representing the preferred range. The upper solid line starts at 10 dB at 300 Hz, decreases to 3 dB at 1000 Hz, and then increases to 7 dB at 7000 Hz. The lower solid line starts at -10 dB at 300 Hz, increases to -3 dB at 500 Hz, remains at -3 dB until 1000 Hz, and then decreases to -18 dB at 7000 Hz. The preferred range is indicated by dotted lines at ±3 dB from the 0 dB reference line between 500 Hz and 3400 Hz.
+
+NOTE – Preferred frequency characteristics are within the dotted lines ( $\pm 3 \text{ dB}$ ). Range of acceptable characteristics is within the solid lines.
+
+FIGURE 3/P.370  
+Magnetic field strength characteristics
+
+## 4.3 Probe coil
+
+### 4.3.1 Dimensions
+
+To minimize the loss of resolution when measuring the magnetic field strength, the following **maximum** dimensions are recommended for the calibrated coil:
+
+|          |                |              |
+|----------|----------------|--------------|
+| Core:    | length:        | 13.5 mm      |
+|          | cross-section: | 1.5 × 2.5 mm |
+| Winding: | length:        | 11 mm        |
+|          | cross-section: | 2.5 × 3.5 mm |
+
+The winding shall be shorter than the core.
+
+#### NOTES
+
+1 The magnetic field may be non-homogeneous within distances comparable to the length of the probe coil. The introduction of magnetic core material may also redirect the magnetic field contours. Typically the sensitivity of the probe coil will increase with frequency at 6 dB/octave.
+
+2 The probe coil may be combined with frequency correcting elements to obtain a flat frequency response over the range of interest.
+
+3 The North American Standard EIA/TIA RS 504 [3], as included in the FCC Rules, Part 68.316 [4], refers to a commercially available probe coil meeting the requirements of this Recommendation.
+
+### 4.3.2 Calibration of the probe coil
+
+In order to calibrate the probe, a homogeneous magnetic field of known intensity shall be available. The magnetic field strength at the centre of a square loop of one turn with a side of “a” metres and carrying a current of “i” amperes is given by:
+
+$$H = \frac{2\sqrt{2}}{\pi} \cdot \frac{i}{a} \quad A/m$$
+
+The dimension “a” should be 0.5 m or more to ensure that the field at the centre is sufficiently well defined in magnitude and direction.
+
+In practice, it may be advantageous to construct the loop having several turns to reduce the current from the source. Essentially, constant current conditions should be maintained over the test frequency range, for example driving the coil from a low impedance generator through a series resistor having at least 100 times the impedance of the coil over the frequency range of interest. If the current drive is monitored during the calibration process, any variations can be taken into account when deriving the probe coil sensitivity.
+
+The test space shall be remote from any field disturbing magnetic material or other material in which eddy currents can be induced, so causing a field disturbance.
+
+The sensitivity as a function of frequency of the probe coil shall be measured as the induced voltage over both leads of the probe coil with an accuracy of  $\pm 0.5$  dB. This voltage is the standard in relation to the applied current per metre and shall be used for the measurement of the requirements specified in 4.2.2.
+
+The total harmonic distortion of the magnetic field shall be less than 1%.
+
+NOTE – Further helpful information is given in IEC Publication 118-1.
+
+### 4.3.3 Distortion
+
+The total harmonic distortion of the probe coil shall be less than 2%, when measuring the field strength up to +2 dB relative to 1 A/m.
+
+# **5 Characteristics of telephone sets that provide additional amplification for the benefit of hearing impaired users**
+
+## **5.1 Introduction**
+
+This clause specifies the requirements for telephones with receive amplification intended to aid the hearing impaired. A significant proportion of the population is disabled by varying degrees of hearing loss, often associated with a reduction of speech discrimination ability. Amplification can only replace the lost sensitivity.
+
+The group most likely to receive the greatest benefit from the use of a telephone with additional receive amplification are those with moderate to severe hearing losses in the range of 35 dB to 80 dB.
+
+In setting the numerical values in this Recommendation, consideration has been given to the fact that the sound pressure levels at the ear during a telephone conversation can be up to 30 dB above those occurring in normal face-to-face conversation (at one metre distance). As hearing impaired people do not necessarily have elevated thresholds of loudness discomfort, some form of output limitation will be required. Recent work has indicated that Automatic Gain Control (AGC) may provide a better automatic means of limitation than peak clipping. In addition, it is recognized that the frequency response to give maximum intelligibility to some hearing impaired people may require shaping.
+
+Two types of application are envisaged. Firstly, where the telephone will be used by persons with a range of hearing acuity, secondly, where the telephone is to be used in the main by a hearing impaired person. In the first, it may be preferable to arrange that the additional amplification is brought into use by the operation of a latching switch that automatically resets the gain to nominal level when the handset is replaced in its rest position. In the second case it will be advantageous to maintain the receive amplification (the level of which is selected by means of a volume control set by the hearing impaired user) when the handset is replaced. The use of voice switched attenuation, perhaps 10 dB to 12 dB, may be necessary to provide protection against instability, in particular for the first case, and could also improve the discrimination against the ambient noise received through the sidetone path.
+
+It is estimated that with the provision of additional amplification to the levels recommended below, possibly up to 80% of hearing impaired users would benefit even when not using their hearing aids to couple to the telephone set. If a hearing aid is worn in addition and inductive coupling is also provided, then the proportion of hearing impaired users who will be able to have satisfactory telephone conversations will increase further. It is, however, pointed out that with a high gain setting selected, the sound level and/or inductive field at the earphone may be considerably higher than normally experienced by hearing aid microphones and/or inductive pick-up coils and, on short telephone connections in particular, there is a very real danger of overloading the input stages of the hearing aid.
+
+The inclusion of additional receiving amplification does not reduce or replace existing technical standards that apply to a handset. Additional receiving amplification can be combined with other additional functionality, such as inductive coupling or additional earpieces, provided specifically for people with special needs.
+
+## **5.2 Sending characteristics**
+
+### **5.2.1 Sensitivity**
+
+It is recommended that when the user is talking, the Sending Loudness Rating (SLR) remains at a constant value set by the requirements of the national system, irrespective of any receive amplification selected.
+
+If voice switching is used in the interests of preserving stability margins and/or Terminal Coupling Loss (TCL) under difficult operating conditions, it is recommended that the switched attenuation be the minimum required for the purpose, e.g. approximately equal to that required to offset any increased receiving amplification selected.
+
+### **5.2.2 Frequency response**
+
+It is recommended that the sending frequency response is maintained according to the requirements of the national system irrespective of any increased receive amplification selected.
+
+## 5.3 Receiving characteristics
+
+### 5.3.1 Sensitivity
+
+In respect of the receive sensitivity, it is recommended that when no additional amplification is selected the Receiving Loudness Rating (RLR) requirements of the national system are met.
+
+With additional receive amplification selected, the RLR may be set up to 20 dB more negative (louder) than the nominal requirements of the national system.
+
+It shall be permissible to set the RLR up to 15 dB more positive (quieter) than the nominal requirements of the national system.
+
+If additional amplification is provided in association with voice switching functions then the principles outlined in 4.6/P.340 are recommended. The depth of switched attenuation should be kept to a minimum in the interests of good speech quality but should be sufficient to maintain stability, return loss and TCL requirements.
+
+### 5.3.2 Frequency response
+
+When no additional amplification is selected, it is recommended that the receive frequency response meets the requirements of the national system.
+
+With additional amplification selected, under some conditions and for particular hearing impaired users, it may be appropriate to provide special frequency shaping. For example, shaping could be provided to compensate for the loss of low frequencies caused by earcap leakage effects that occur with most types of telephone earphone. Earphones having low acoustic impedance are an exception to this (see Note 2, Foreword). An alternative shaping might be to provide additional gain at high frequencies to compensate for their loss over long local subscriber lines. Any frequency shaping provided could be by means of an additional control.
+
+NOTE – In practice, when coupling to a hearing aid inductively or acoustically, the low frequencies are normally missing, and for acoustic coupling to conventional earphones there is usually a slope of 12 to 18 dB per octave at frequencies below the first mechanical resonance, often around 1500 Hz. Some examples are shown in Appendix I.
+
+### 5.3.3 Restoring normal receive amplification
+
+**Option A** – Telephones to be used by any user
+
+At the termination of the telephone conversation any additional amplification selected shall be cancelled and the nominal RLR values restored by the action of replacing the handset to its rest position, or an equivalent action.
+
+**Option B** – Telephones to be used mainly by a hearing impaired user
+
+For the benefit of a hearing impaired user frequently using the terminal, the option may be provided for the additional amplification selected during a telephone conversation to be locked in position. If this option is provided, additional measures to ensure stability with maximum gain selected may be necessary.
+
+## 5.4 Sidetone
+
+It is recommended that sidetone levels (STMR, LSTR) indicated in Recommendation G.121 be provided when additional amplification is not in use.
+
+With additional amplification selected, it will normally only be possible to maintain recommended sidetone levels if voice switching techniques are used.
+
+# **6 Electrical coupling of telephone sets to hearing aids**
+
+## **6.1 Introduction**
+
+This clause covers the possibility of electrical coupling from a telephone set to a hearing aid. It is intended to be compatible with the IEC Publication 118-6, which covers the characteristics of electrical input ports for hearing aids.
+
+It is also envisaged that it could be used in other applications that require electrical connection to the PSTN, for example to couple into other non-telephony amplification systems such as public address, or recording systems. Another alternative would be the direct electrical connection to a hearing aid transducer or headset, given that the device had sufficient sensitivity. This clause may also find application for mobile apparatus and apparatus having cordless handsets that provide for electrical coupling to hearing aids. Some of the applications envisaged would need to address safety and/or protection issues and, although these and the applications themselves do not come within the scope of ITU Recommendations, attention is drawn to them here for information.
+
+## **6.2 Electrical characteristics**
+
+Unless otherwise stated all the requirements given below are for the volume control (if present) set to give the maximum output.
+
+### **6.2.1 Point of connection in the telephone set**
+
+It is recommended that the interconnection to the hearing aid be taken from the electrical path to the handset earphone so that the sidetone path is coupled into the hearing aid. It is also recommended that it shall not be possible to inject a signal into the telecommunication network from this point.
+
+### **6.2.2 Electrical characteristics at interconnection point**
+
+In what follows it is assumed that the load normally applied by a hearing aid input circuit will be 2000 ohms resistive.
+
+#### **6.2.2.1 Calibration of the acoustic receive level**
+
+Using the measurement configuration shown in Figure 1 for analogue telephones and Figure 2 for digital telephones, the drive level of the oscillator shall be adjusted to produce a sound level of  $-14$  dBPa at 1000 Hz at the ERP (Ear Reference Point). This drive level shall be used for measuring the impedance, sensitivity and frequency characteristics recommended below.
+
+#### **6.2.2.2 Impedance**
+
+The modulus of the electrical source impedance between the frequencies of 300 and 4000 Hz shall be less than 1000 ohms for all settings of the volume control (if present).
+
+#### **6.2.2.3 Sensitivity**
+
+With the drive level of the oscillator set as in 6.2.2.1 above, at 1000 Hz, the electrical output at 1000 Hz shall be  $-35 \pm 5$  dBV. With the volume control (if present) set to minimum the electrical output shall be between 15 dB and 30 dB lower than the output at the maximum setting.
+
+#### **6.2.2.4 Frequency characteristic**
+
+With the drive level of the oscillator set as in 6.2.2.1 above, the frequency response at the telephone electrical interconnection point, when loaded with  $2\text{ k}\Omega$ , shall be equal to the sensitivity at 1000 Hz  $\pm 3$  dB over the range 300 to 4000 Hz and  $\pm 5$  dB over the range 100 to 300 Hz for all settings of the volume control (if present).
+
+#### **6.2.2.5 Noise**
+
+With the oscillator in 6.2.2.1 replaced by a 600 ohm resistor the noise level at the electrical interconnection point shall be less than  $-70$  dBVp r.m.s.
+
+#### **6.2.2.6 Maximum output**
+
+With the oscillator in 6.2.2.1 set to give  $+20$  dBV r.m.s. the maximum output at the electrical interconnection point shall be limited to  $0$  dBV.
+
+#### **6.2.2.7 Insulation**
+
+In order to prevent direct electrical connection with the PSTN it is recommended that the interconnection point be electrically isolated by use of, for example, a transformer. It is recommended that the insulation provided should meet the requirements of the national system.
+
+## **6.3 Interconnection with the telephone set**
+
+### **6.3.1 Connector type**
+
+The connection shall be by means of a socket which is compatible with a miniature coaxial, stereo jack plug, type 130-8 IEC, conforming to IEC 268-11. Normally the socket shall be of 3.5 mm diameter. Alternatively, for compact telephone sets such as cordless or mobile telephones, the socket may be of 2.5 mm diameter.
+
+### **6.3.2 Connector position**
+
+It is recommended that the connector socket should be positioned on the telephone for high visibility and ease of inserting the plug. This means that the socket should be placed on the front edge, front top side or on the front sides of the subset housing. The socket should be placed so that the plug and lead will not interfere with the normal operation of the telephone, i.e. lifting/replacing the handset, dialling, inserting coins or cards, or any other functions. On public telephones it is important that the socket is not positioned on a horizontal surface making it susceptible to the ingress of fluids or other contaminants. Telephones and mobile telephones with cordless handsets shall not have the connector on the handset but on the body of the subset.
+
+One-piece telephones, cordless telephones and mobile telephones which have no separate handset, the socket should be positioned so that the plug and the lead will not interfere with the normal operation of the instrument, i.e. holding it, dialling, charging batteries, or any other function.
+
+## **6.4 Safety issues**
+
+It is recommended that other safety issues associated with the interconnection point should meet the requirements of the national system.
+
+# Annex A
+
+## Measurement of an acousto-magnetic adapter generating a magnetic field
+
+(This annex forms an integral part of this Recommendation)
+
+## A.1 Measurement procedures
+
+Measurements are made in accordance with this Recommendation.
+
+The output sound pressure level of the telephone receiver is measured against the artificial ear without the acousto-magnetic adapter being mounted.
+
+The characteristics of the magnetic field of the acousto-magnetic adapter are measured when mounted on the actual telephone receiver.
+
+NOTE – In reporting results, the type of telephone set used should be specified.
+
+## A.2 Magnetic field requirements
+
+The magnetic field produced by the adapter when fitted to a handset should meet the level and frequency characteristic requirements given in 4.2.1 and 4.2.2.
+
+## A.3 Physical properties
+
+Desirable physical properties of the acousto-magnetic adapter are:
+
+- easy to place on the earcap and remove again;
+- a firm contact to the earcap so that the acousto-magnetic adapter and the telephone handset can be used as an integral unit;
+- forming a good and well-defined acoustic coupling to the earcap (see Note);
+- the surface of the acousto-magnetic adapter defining the adapter plane should be flat or should have a shape easily defining the adapter plane;
+- the adapter plane should be approximately parallel to the earcap plane;
+- the magnetic field produced by the adapter should be orientated so that the magnetic coupling to the hearing aid is only to a small extent dependent on the position of the hearing aid.
+
+NOTE – The inner diameter of an acoustic seal is recommended to be equal to the edge diameter of the IEC 318 artificial ear (see Recommendation P.57).
+
+# Appendix I
+
+## Examples of frequency characteristics of hearing aids coupled to telephones
+
+(This appendix does not form an integral part of this Recommendation)
+
+Figures I.1 to I.9 have been taken from [1] and illustrate the signals arriving at the Drum Reference Point (DRP) of a Head And Torso Simulator (HATS). Figure I.2 refers to the IRS (see Recommendation P.48) sending and receiving ends joined directly together and having an OLR by definition of 0 dB. All other figures are for a British Telecom Tribune set coupled to various UK hearing aids, (except where the Beocom telephone is mentioned) driven from the equivalent of the IRS send end with 10 dB additional loss. Thus the “connection” is what might be termed “typical” having an OLR approximating to 10 dB, i.e. similar to the ITU-T long-term aim for OLR.
+
+Note particularly the rising frequency characteristics under all coupled conditions.
+
+### Telephony
+
+| Sound level @ MRP       | Loss   | Sound level @ ERP          |
+|-------------------------|--------|----------------------------|
+| 89.3 dB SPL (pure tone) | 1.1 dB | 88.2 dB SPL (1 kHz)        |
+| 88.8 dB SPL (Speech)    | 5.5 dB | 83.3 dB SPL (0.2 to 4 kHz) |
+
+![Diagram of a telephone speech path showing Mouth, Handset (at MRP), IRS, Send, 10 dB loss, IRS, Rec., and Speech path.](2cde062fd82833415971a8bd1a2cafab_img.jpg)
+
+The diagram illustrates a telephone speech path. It starts with a 'Mouth' connected to a 'Handset' (labeled 'at MRP'). The signal then passes through an 'IRS' (Input Resistor) to a 'Send' block. A '10 dB' loss is indicated between the 'Send' block and another 'IRS' block. The signal then passes through the second 'IRS' to a 'Rec.' (Receiver) block, which is connected to a 'Speech path' (represented by a handset icon). The reference 'T1208470-96/d04' is noted at the bottom right.
+
+Diagram of a telephone speech path showing Mouth, Handset (at MRP), IRS, Send, 10 dB loss, IRS, Rec., and Speech path.
+
+### Metre air path
+
+|                                       |         |                                                |
+|---------------------------------------|---------|------------------------------------------------|
+| 89.3 dB SPL (Speech)<br>(100-8000 Hz) | 30.2 dB | 59.1 dB SPL (Free field)                       |
+|                                       | 29.0 dB | 63.3 dB SPL<br>(including room & head effects) |
+| 88.8 dB SPL (Speech)<br>(200-4000 Hz) | 28.9 dB | 62.9 dB SPL<br>(including room & head effects) |
+
+FIGURE I.1/P.370
+
+**Speech path mouth to ear losses for a typical telephone connection, having an OLR of 10 dB, and a metre air path**
+
+![Graph comparing speech via a telephone (Loosely coupled, Sealed) and 1-metre air path across frequencies from 250 to 4000 Hz.](250cf77a1cd51989da09fca796b3e4ea_img.jpg)
+
+The graph plots dB SPL (Y-axis, 40 to 90) against Frequency (X-axis, 250 to 4000 Hz). It compares three speech transmission methods:
+ 
+
+- Loosely coupled** (black line with diamond markers): Shows a rising trend from approximately 40 dB SPL at 250 Hz to a peak of about 88 dB SPL at 2500 Hz, followed by a sharp drop to 65 dB SPL at 4000 Hz.
+- Sealed** (grey line with square markers): Shows a rising trend from approximately 60 dB SPL at 250 Hz to a peak of about 85 dB SPL at 630 Hz, then a slight decline to 65 dB SPL at 4000 Hz.
+- 1 metre air path** (grey line with triangle markers): Shows a relatively flat trend, starting around 45 dB SPL at 250 Hz and ending around 40 dB SPL at 4000 Hz.
+
+ The reference 'T1208480-96/d05' is noted at the bottom right.
+
+Graph comparing speech via a telephone (Loosely coupled, Sealed) and 1-metre air path across frequencies from 250 to 4000 Hz.
+
+FIGURE I.2/P.370
+
+**Comparison of speech via a telephone and 1-metre air path**
+
+![Line graph showing dB SPL vs Frequency for BE17 over mic, BE17 over ear, and Room noise. The graph shows three data series: BE17 over mic (black diamonds), BE17 over ear (grey squares), and Room noise (grey triangles). The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 60 to 120 dB. BE17 over ear shows the highest output, peaking at approximately 115 dB SPL at 2000 Hz. BE17 over mic peaks at approximately 105 dB SPL at 2000 Hz. Room noise is relatively flat, peaking at approximately 85 dB SPL between 1250 and 1500 Hz.](b53846f262c6904a1b45abef2e95fbd8_img.jpg)
+
+| Frequency (Hz) | BE17 over mic (dB SPL) | BE17 over ear (dB SPL) | Room noise (dB SPL) |
+|----------------|------------------------|------------------------|---------------------|
+| 200            | 70                     | 70                     | 70                  |
+| 250            | 72                     | 75                     | 70                  |
+| 315            | 75                     | 75                     | 70                  |
+| 400            | 78                     | 80                     | 78                  |
+| 500            | 80                     | 85                     | 78                  |
+| 630            | 85                     | 90                     | 80                  |
+| 800            | 90                     | 98                     | 85                  |
+| 1000           | 98                     | 105                    | 85                  |
+| 1250           | 100                    | 108                    | 88                  |
+| 1500           | 102                    | 109                    | 85                  |
+| 2000           | 105                    | 110                    | 80                  |
+| 2500           | 108                    | 115                    | 83                  |
+| 3150           | 100                    | 110                    | 80                  |
+| 4000           | 78                     | 88                     | 70                  |
+
+Line graph showing dB SPL vs Frequency for BE17 over mic, BE17 over ear, and Room noise. The graph shows three data series: BE17 over mic (black diamonds), BE17 over ear (grey squares), and Room noise (grey triangles). The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 60 to 120 dB. BE17 over ear shows the highest output, peaking at approximately 115 dB SPL at 2000 Hz. BE17 over mic peaks at approximately 105 dB SPL at 2000 Hz. Room noise is relatively flat, peaking at approximately 85 dB SPL between 1250 and 1500 Hz.
+
+- ◆— BE17 over mic.
+- BE17 over ear
+- ▲— Room noise
+
+FIGURE I.3/P.370  
+**Acoustic coupling – effect of position**
+
+![Line graph showing dB SPL vs Frequency for Classic IE and Room noise. The graph shows two data series: Classic IE (black diamonds) and Room noise (grey squares). The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 60 to 120 dB. Classic IE shows a significant increase in output starting around 250 Hz, peaking at approximately 115 dB SPL at 1500 Hz, and then decreasing. Room noise is relatively flat, peaking at approximately 70 dB SPL between 1250 and 2000 Hz.](1a6a826cc13d4e964b7bda69508d78e6_img.jpg)
+
+| Frequency (Hz) | Classic IE (dB SPL) | Room noise (dB SPL) |
+|----------------|---------------------|---------------------|
+| 200            | 65                  | 65                  |
+| 250            | 75                  | 70                  |
+| 315            | 80                  | 70                  |
+| 400            | 88                  | 65                  |
+| 500            | 92                  | 65                  |
+| 630            | 98                  | 63                  |
+| 800            | 102                 | 63                  |
+| 1000           | 105                 | 63                  |
+| 1250           | 112                 | 70                  |
+| 1500           | 115                 | 70                  |
+| 2000           | 112                 | 70                  |
+| 2500           | 108                 | 68                  |
+| 3150           | 92                  | 58                  |
+| 4000           | 85                  | -                   |
+
+Line graph showing dB SPL vs Frequency for Classic IE and Room noise. The graph shows two data series: Classic IE (black diamonds) and Room noise (grey squares). The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 60 to 120 dB. Classic IE shows a significant increase in output starting around 250 Hz, peaking at approximately 115 dB SPL at 1500 Hz, and then decreasing. Room noise is relatively flat, peaking at approximately 70 dB SPL between 1250 and 2000 Hz.
+
+FIGURE I.4/P.370  
+**Acoustic coupling – in the ear aid (Classic)**
+
+![Line graph showing dB SPL vs Frequency for Tribune KEMAR and Beocom KEMAR. The x-axis represents Frequency from 250 to 4000 Hz, and the y-axis represents dB SPL from 30 to 100. Tribune KEMAR (black diamonds) starts at ~35 dB SPL at 250 Hz, rises to ~95 dB SPL at 2000 Hz, and drops to ~72 dB SPL at 4000 Hz. Beocom KEMAR (grey squares) starts at ~55 dB SPL at 250 Hz, rises to ~98 dB SPL at 2500 Hz, and drops to ~85 dB SPL at 4000 Hz.](b2d16e07bfa79d67a8adabf7e26c7764_img.jpg)
+
+| Frequency (Hz) | Tribune KEMAR (dB SPL) | Beocom KEMAR (dB SPL) |
+|----------------|------------------------|-----------------------|
+| 250            | 35                     | 55                    |
+| 315            | 45                     | 68                    |
+| 400            | 55                     | 75                    |
+| 500            | 60                     | 78                    |
+| 630            | 68                     | 80                    |
+| 800            | 75                     | 81                    |
+| 1000           | 85                     | 82                    |
+| 1250           | 90                     | 83                    |
+| 1600           | 95                     | 88                    |
+| 2000           | 95                     | 98                    |
+| 2500           | 95                     | 98                    |
+| 3150           | 90                     | 98                    |
+| 4000           | 72                     | 85                    |
+
+Line graph showing dB SPL vs Frequency for Tribune KEMAR and Beocom KEMAR. The x-axis represents Frequency from 250 to 4000 Hz, and the y-axis represents dB SPL from 30 to 100. Tribune KEMAR (black diamonds) starts at ~35 dB SPL at 250 Hz, rises to ~95 dB SPL at 2000 Hz, and drops to ~72 dB SPL at 4000 Hz. Beocom KEMAR (grey squares) starts at ~55 dB SPL at 250 Hz, rises to ~98 dB SPL at 2500 Hz, and drops to ~85 dB SPL at 4000 Hz.
+
+- ◆— Tribune KEMAR
+- Beocom KEMAR
+
+FIGURE I.5/P.370  
+**Effect of low acoustic impedance on response**
+
+![Line graph showing dB SPL vs Frequency for Tribune/BE51/max and Beocom/BE51/Max. The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 80 to 130. Tribune/BE51/max (black diamonds) starts at ~80 dB SPL at 200 Hz, rises to ~125 dB SPL at 2000 Hz, and drops to ~100 dB SPL at 3150 Hz. Beocom/BE51/Max (grey squares) starts at ~88 dB SPL at 200 Hz, rises to ~128 dB SPL at 2500 Hz, and drops to ~108 dB SPL at 3150 Hz.](1c427123350e0e73e2a109b79069314b_img.jpg)
+
+| Frequency (Hz) | Tribune/BE51/max (dB SPL) | Beocom/BE51/Max (dB SPL) |
+|----------------|---------------------------|--------------------------|
+| 200            | 80                        | 88                       |
+| 250            | 83                        | 92                       |
+| 315            | 87                        | 98                       |
+| 400            | 92                        | 104                      |
+| 500            | 97                        | 109                      |
+| 630            | 102                       | 112                      |
+| 800            | 109                       | 114                      |
+| 1000           | 115                       | 117                      |
+| 1250           | 118                       | 117                      |
+| 1600           | 118                       | 117                      |
+| 2000           | 125                       | 122                      |
+| 2500           | 128                       | 128                      |
+| 3150           | 120                       | 122                      |
+| 4000           | 100                       | 108                      |
+
+Line graph showing dB SPL vs Frequency for Tribune/BE51/max and Beocom/BE51/Max. The x-axis represents Frequency from 200 to 3150 Hz, and the y-axis represents dB SPL from 80 to 130. Tribune/BE51/max (black diamonds) starts at ~80 dB SPL at 200 Hz, rises to ~125 dB SPL at 2000 Hz, and drops to ~100 dB SPL at 3150 Hz. Beocom/BE51/Max (grey squares) starts at ~88 dB SPL at 200 Hz, rises to ~128 dB SPL at 2500 Hz, and drops to ~108 dB SPL at 3150 Hz.
+
+- ◆— Tribune/BE51/max
+- Beocom/BE51/Max
+
+FIGURE I.6/P.370  
+**Effect of low acoustic impedance on coupling to BE51 hearing aid**
+
+![Line graph showing dB SPL at DRP vs Frequency Hz for BE17 inductive coupling. The graph compares 'BE17 ind.' (black diamonds) and 'Room noise' (grey squares) across frequencies from 200 Hz to 3150 Hz. The BE17 ind. curve shows a peak around 1250-1500 Hz, while the Room noise curve is relatively flat.](3102c32204f998dba666e1e915d5babf_img.jpg)
+
+| Frequency Hz | BE17 ind. (dB SPL at DRP) | Room noise (dB SPL at DRP) |
+|--------------|---------------------------|----------------------------|
+| 200          | 65                        | 48                         |
+| 250          | 73                        | 51                         |
+| 315          | 79                        | 47                         |
+| 400          | 86                        | 48                         |
+| 500          | 91                        | 49                         |
+| 630          | 96                        | 56                         |
+| 800          | 101                       | 57                         |
+| 1000         | 106                       | 64                         |
+| 1250         | 108                       | 71                         |
+| 1500         | 108                       | 63                         |
+| 1800         | 107                       | 62                         |
+| 2200         | 108                       | 67                         |
+| 2800         | 105                       | 62                         |
+| 3150         | 89                        | 51                         |
+
+T1208530-96/d10
+
+Line graph showing dB SPL at DRP vs Frequency Hz for BE17 inductive coupling. The graph compares 'BE17 ind.' (black diamonds) and 'Room noise' (grey squares) across frequencies from 200 Hz to 3150 Hz. The BE17 ind. curve shows a peak around 1250-1500 Hz, while the Room noise curve is relatively flat.
+
+FIGURE I.7/P.370  
+**Inductive coupling – BE17 aid over a typical connection**
+
+![Line graph showing dB SPL DRP vs Frequency Hz for inductively coupled Classic in the ear aid. The graph compares 'Classic ind./typical' (black diamonds) and '1-metre air path' (grey squares) across frequencies from 200 Hz to 3150 Hz. The Classic ind./typical curve shows a peak around 1500 Hz, while the 1-metre air path curve is relatively flat.](96a7eac66ef72bb016c280278506ac63_img.jpg)
+
+| Frequency Hz | Classic ind./typical (dB SPL DRP) | 1-metre air path (dB SPL DRP) |
+|--------------|-----------------------------------|-------------------------------|
+| 200          | 39                                | 48                            |
+| 250          | 43                                | 49                            |
+| 315          | 48                                | 50                            |
+| 400          | 52                                | 51                            |
+| 500          | 56                                | 50                            |
+| 630          | 58                                | 49                            |
+| 800          | 68                                | 48                            |
+| 1000         | 76                                | 46                            |
+| 1250         | 83                                | 44                            |
+| 1500         | 84                                | 43                            |
+| 1800         | 77                                | 49                            |
+| 2200         | 72                                | 53                            |
+| 2800         | 76                                | 49                            |
+| 3150         | 74                                | 45                            |
+
+T1208540-96/d11
+
+Line graph showing dB SPL DRP vs Frequency Hz for inductively coupled Classic in the ear aid. The graph compares 'Classic ind./typical' (black diamonds) and '1-metre air path' (grey squares) across frequencies from 200 Hz to 3150 Hz. The Classic ind./typical curve shows a peak around 1500 Hz, while the 1-metre air path curve is relatively flat.
+
+FIGURE I.8/P.370  
+**Inductively coupled Classic in the ear aid over a typical connection**
+
+![Line graph showing dB SPL DRP vs Frequency Hz for BE31/ind./typical and 1-metre air path. The BE31/ind./typical curve peaks at 120 dB SPL DRP around 2000 Hz, while the 1-metre air path curve remains relatively flat around 50 dB SPL DRP.](5ed9189841659dfb01f809b8e3b21f74_img.jpg)
+
+| Frequency (Hz) | BE31/ind./typical (dB SPL DRP) | 1-metre air path (dB SPL DRP) |
+|----------------|--------------------------------|-------------------------------|
+| 200            | 80                             | 50                            |
+| 315            | 95                             | 50                            |
+| 500            | 105                            | 50                            |
+| 800            | 115                            | 50                            |
+| 1250           | 118                            | 48                            |
+| 1600           | 118                            | 45                            |
+| 2000           | 120                            | 50                            |
+| 2500           | 120                            | 55                            |
+| 3150           | 118                            | 50                            |
+| 4000           | 102                            | 45                            |
+
+Line graph showing dB SPL DRP vs Frequency Hz for BE31/ind./typical and 1-metre air path. The BE31/ind./typical curve peaks at 120 dB SPL DRP around 2000 Hz, while the 1-metre air path curve remains relatively flat around 50 dB SPL DRP.
+
+FIGURE 1.9/P.370  
+**Inductively coupled BE31 aid over a typical connection**
+
+# Appendix II
+
+## Bibliography
+
+(This appendix does not form an integral part of this Recommendation)
+
+- [1] BARNES (G.J.): What do we hear through the telephone?, *British Society of Audiologists*, Leeds, April 1996.
+- [2] GLEISS, (N.): Preferred listening levels in telephony, *Tele Engl. Ed.*, No. 2, 1974.
+- [3] EIA/TIA RS 504: *North American Standard*.
+- [4] FCC Rules, Part 68.316.
+
+
+
+# ITU-T RECOMMENDATIONS SERIES
+
+- Series A Organization of the work of the ITU-T
+- Series B Means of expression
+- Series C General telecommunication statistics
+- Series D General tariff principles
+- Series E Telephone network and ISDN
+- Series F Non-telephone telecommunication services
+- Series G Transmission systems and media
+- Series H Transmission of non-telephone signals
+- Series I Integrated services digital network
+- Series J Transmission of sound-programme and television signals
+- Series K Protection against interference
+- Series L Construction, installation and protection of cables and other elements of outside plant
+- Series M Maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits
+- Series N Maintenance: international sound-programme and television transmission circuits
+- Series O Specifications of measuring equipment
+- Series P Telephone transmission quality**
+- Series Q Switching and signalling
+- Series R Telegraph transmission
+- Series S Telegraph services terminal equipment
+- Series T Terminal equipments and protocols for telematic services
+- Series U Telegraph switching
+- Series V Data communication over the telephone network
+- Series X Data networks and open system communication
+- Series Z Programming languages

marked/P/T-REC-P.380-202207-I_PDF-E/raw.md

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+
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**P.380**
+
+(07/2022)
+
+SERIES P: TELEPHONE TRANSMISSION QUALITY,  
+TELEPHONE INSTALLATIONS, LOCAL LINE  
+NETWORKS
+
+Voice terminal characteristics
+
+# --- **Electro-acoustic measurements on headsets**
+
+Recommendation ITU-T P.380
+
+## ITU-T P-SERIES RECOMMENDATIONS
+
+## TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS
+
+|                                                                                                    |                    |
+|----------------------------------------------------------------------------------------------------|--------------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality      | P.10–P.19          |
+| Voice terminal characteristics                                                                     | P.30–P.39          |
+| Reference systems                                                                                  | P.40–P.49          |
+| Objective measuring apparatus                                                                      | P.50–P.59          |
+| Objective electro-acoustical measurements                                                          | P.60–P.69          |
+| Measurements related to speech loudness                                                            | P.70–P.79          |
+| Methods for objective and subjective assessment of speech quality                                  | P.80–P.89          |
+| <b>Voice terminal characteristics</b>                                                              | <b>P.300–P.399</b> |
+| Objective measuring apparatus                                                                      | P.500–P.599        |
+| Measurements related to speech loudness                                                            | P.700–P.709        |
+| Methods for objective and subjective assessment of speech and video quality                        | P.800–P.899        |
+| Audiovisual quality in multimedia services                                                         | P.900–P.999        |
+| Transmission performance and QoS aspects of IP end-points                                          | P.1000–P.1099      |
+| Communications involving vehicles                                                                  | P.1100–P.1199      |
+| Models and tools for quality assessment of streamed media                                          | P.1200–P.1299      |
+| Telemeeting assessment                                                                             | P.1300–P.1399      |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                  | P.1400–P.1499      |
+| Methods for objective and subjective assessment of quality of services other than speech and video | P.1500–P.1599      |
+
+For further details, please refer to the list of ITU-T Recommendations.
+
+## Recommendation ITU-T P.380
+
+# Electro-acoustic measurements on headsets
+
+## Summary
+
+Recommendation ITU-T P.380 provides testing methods for headsets using the head and torso simulator. The Recommendation addresses the following topics: selection of artificial ears, classification of headsets, positioning of headsets on the head and torso simulator (HATS), test repeatability and contents of the measurement report.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T P.380    | 2003-11-13 | 12          | <a href="http://handle.itu.int/11.1002/1000/7040">11.1002/1000/7040</a>   |
+| 2.0     | ITU-T P.380    | 2022-07-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/15003">11.1002/1000/15003</a> |
+
+## Keywords
+
+Artificial ear, head and torso simulator, headsets, testing methods.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents/software copyrights, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2022
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                   | Page |
+|---------------------------------------------------|------|
+| 1 Scope .....                                     | 1    |
+| 2 References.....                                 | 1    |
+| 3 Definitions .....                               | 1    |
+| 3.1 Terms defined elsewhere .....                 | 1    |
+| 3.2 Terms defined in this Recommendation.....     | 1    |
+| 4 Abbreviations and acronyms .....                | 2    |
+| 5 Conventions .....                               | 2    |
+| 6 Types of headsets.....                          | 2    |
+| 6.1 Receiver .....                                | 2    |
+| 6.2 Microphone.....                               | 2    |
+| 7 Artificial ear selection.....                   | 3    |
+| 8 Positioning and measurement of the headset..... | 3    |
+| 8.1 Measurements.....                             | 3    |
+| 8.2 Positioning.....                              | 3    |
+| 9 Test repeatability .....                        | 4    |
+| 10 Measurement report.....                        | 5    |
+| Bibliography.....                                 | 6    |
+
+
+
+# Electro-acoustic measurements on headsets
+
+## 1 Scope
+
+This Recommendation is the result of a study held within ITU-T for defining the electro-acoustic testing methodologies for headsets, which provide the best correlation with the performance of headsets in real use, when using the couplers currently recommended in [ITU-T P.57].
+
+The results of this round robin test, aiming to compare the acoustic behaviour of headsets placed on humans and on the head and torso simulator (HATS), can be found in the Bibliography.
+
+The recommended test methodology is based on the use of HATS, as this is the best approximation of acoustical conditions occurring in the real use of headsets.
+
+This Recommendation focuses specifically on headsets and overrules [ITU-T P.57] regarding the applicability rules of artificial ears to specific receivers, as long as these devices belong to the headsets.
+
+This Recommendation is complementary to the relevant [ITU-T P.64], [ITU-T P.79], etc., which specify the electro-acoustic and telephonometric testing methods that are applicable to the telephone devices.
+
+The recommendation of performance descriptors, such as masks or limit values, is left to the relevant performance standards.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T P.57] Recommendation ITU-T P.57 (2021), *Artificial ears*.
+- [ITU-T P.64] Recommendation ITU-T P.64 (2022), *Determination of sensitivity/frequency characteristics of local telephone systems*.
+- [ITU-T P.79] Recommendation ITU-T P.79 (2007), *Calculation of loudness ratings for telephone sets*.
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+None.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+- 3.2.1 CL: Centre of lips of head and torso simulator.
+
+**3.2.2 headset:** Apparatus for telephony comprising essentially a "hands-free" handset which is typically secured to the head of the wearer. It includes a telephone microphone and a telephone receiver.
+
+**3.2.3 recommended test position (RTP):** Corresponds to the position in which the headset should be placed on HATS, e.g., as instructed by the manufacturer. In all the cases, the RTP should resemble the RWP on humans.
+
+**3.2.4 recommended wearing position (RWP):** Corresponds to the position in which a headset should be placed on humans according to the intended use (e.g., as instructed by the manufacturer in the user manual, etc.).
+
+## **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                              |
+|------|------------------------------|
+| HATS | Head And Torso Simulator     |
+| RTP  | Recommended Test Position    |
+| RWP  | Recommended Wearing Position |
+| RLR  | Receive Loudness Rating      |
+| STMR | Sidetone Masking Rating      |
+
+## **5 Conventions**
+
+None.
+
+## **6 Types of headsets**
+
+This Recommendation covers the headsets equipped with receivers and microphones as defined below.
+
+### **6.1 Receiver**
+
+With reference to the definitions provided in [ITU-T P.57], the following receiver types are covered:
+
+- Insert-type;
+- Intra-concha;
+- Supra-concha;
+- Supra-aural.
+
+### **6.2 Microphone**
+
+This Recommendation covers headsets equipped with microphones positioned as follows:
+
+- In front of and around the mouth (e.g., long booms);
+- At the cheek (e.g., short booms);
+- At the ear;
+- At the neck (e.g., hanging down or collar clip);
+- At the chest (e.g., hanging down or clip).
+
+## 7 Artificial ear selection
+
+Type 4.3 artificial ear is preferred for insert-type headsets, intra-concha headsets, supra-concha headsets and supra-aural headsets.
+
+Type 4.4 artificial ear is preferred for insert-type headsets<sup>1</sup>, intra-concha headsets, supra-concha headsets and Supra-aural headsets.
+
+Type 3.3 artificial ear may be used for insert-type headsets<sup>2</sup>, intra-concha headsets, supra-concha headsets and supra-aural headsets.
+
+Type 3.4 artificial ear may be used for insert-type headsets<sup>2</sup> and intra-concha<sup>3</sup> headsets.
+
+In case artificial ears of Type 3 are used and obtain different measurement results against Type 4 artificial ears, the results from Type 4 artificial ear shall take precedence.
+
+## 8 Positioning and measurement of the headset
+
+### 8.1 Measurements
+
+The positioning methodology provided in this Recommendation has been validated [b-ITU-T SG12 Cont54], [b-ITU-T SG12 Cont47], and shall be used, for measuring the frequency response and loudness ratings [ITU-T P.79] for both receive and send directions.
+
+This positioning of the headset on the HATS is, however, also recommended for performing measurements related to other electro-acoustic parameters such as sidetone masking rating (STMR), D-factor, distortion, etc.
+
+Furthermore, special conditions apply to headsets in some respects.
+
+Some headsets are binaural devices. In case the required receive loudness rating (RLR) is only specified for a monaural device, the corresponding required RLR for a binaural device should be 6 dB higher (for each of the receivers measured separately). In a similar way, other receive related requirements should be adapted for binaural devices.
+
+### 8.2 Positioning
+
+For a given headset, one single position shall be defined to test all the electro-acoustic parameters on a given HATS.
+
+The reasons for this provision are the following:
+
+- This is close to what happens in real life, so this procedure is consistent with the basic goal of the Recommendation, e.g., resembling the real-use conditions;
+- It is simple;
+- It allows for sidetone (and other related) measurements to be performed.
+
+The positioning of the headset shall reflect the way it is intended by the manufacturer to be used in a real situation.
+
+---
+
+<sup>1</sup> The Type 4.4 artificial ear simulator cannot be used for insert-type headsets where the acoustic outlet of the receiver is placed beyond the reference plane in the ear canal of the Type 4.4 artificial ear.
+
+<sup>2</sup> It should be noted that, in some cases, the use of Type 3.3 or Type 3.4 ear simulator with an insert headset could provide a seal greater than that occurring on humans, leading to an overestimation of the level of the frequency response curve in the low frequency region (below 1 kHz). This is especially true for headsets relying on a close sealing with the ear canal.
+
+<sup>3</sup> Only for intra-concha headsets where the acoustic outlet of the receiver face towards the ear canal the Type 3.4 artificial ear can be used.
+
+For this reason, the manufacturer's user's guide should provide a recommended wearing position describing in a precise way how the device should be placed on the user's head.
+
+From this recommended wearing position (RWP), the recommended test position shall be derived, as close as possible to the RWP.
+
+Also, the RTP description should hopefully be provided by the manufacturer and shall state in which way the receiving part of the headset shall be placed against or inside the ear simulator, and describe the positioning of the microphone, once the receiver(s) of the headset has been placed on the ear simulator.
+
+The exact positioning of the microphone shall be specified by using geometric coordinates relative to the centre of the lips.
+
+NOTE – A good laboratory practice may refer to [ITU-T P.64], which defines "a set of Cartesian axes with origin at CL, the centre of the lips", and further defines the axes as follows:
+
+- x-axis: horizontal axis of the mouth, with positive direction into the mouth;
+- y-axis: horizontal, perpendicular to the x-axis, with positive direction towards the side of the mouth on which the handset is held;
+- z-axis: vertical, with positive direction upwards.
+
+The way in which the coordinates are defined and checked is left to the choice of the manufacturer, or of the test lab in case the RTP is not defined by the manufacturer, but it should be noted that the closer the microphone is to the mouth, the more sensitive the results will be to any inaccuracy of the geometrical positioning.
+
+As an essential complementary information, the manufacturer shall state what is the recommended orientation of the microphone towards the mouth.
+
+In the case where no RWP information is available for the headset under test, then a suitable RWP and the derived RTP shall be defined by the testing lab, aiming at best-guessing the expected real-use position. All the relevant parameters of these assumed positions shall be reported together with the measurement results.
+
+## 9 Test repeatability
+
+Due to the sensitivity of the test results to the headset positioning, the tests shall be repeated at least five times by completely repositioning the headset, following the rules described in this Recommendation.
+
+The test report shall individually provide the test results for each repetition, plus any additional statistical analysis as required.
+
+NOTE 1 – It is recommended that the test operators get acquainted with the specific headset characteristics by running some preliminary learning test sessions.
+
+NOTE 2 – The use of positioning jigs can improve the test repeatability so that no repetition is required. This generally applies to all tests from test repetitions carried out by a single operator to tests carried out at different laboratories. However, the jig must be customized or adjusted for the particular type of headset under test, fully respecting the positioning principles outlined for the RTP. The purpose of the jig is to reduce the variability of test results, especially for microphones, without changing the mean of the test results. Thus, care must be taken to validate the designed jig for its intended use, and it should be verified that the jig does not introduce a bias to the results (i.e., the jig should be verified by comparing the mean of results obtained with and without the jig).
+
+## **10 Measurement report**
+
+The following information shall be reported additionally to the generally requested information:
+
+- Precise description of the positioning of the headset used for the tests, along with pictures when relevant.
+- The number of measurements taken into account in the calculation of the statistic parameters.
+
+## Bibliography
+
+- [b-ITU-T P.58] Recommendation ITU-T P.58 (2021), *Head and torso simulator for telephonometry*.
+- [b-ITU-T SG12 Cont54] ITU-T SG12 Study Period 2001 Contribution 54 (2003), *Conclusions of the Round Robin Test on headsets: Receiving side*.  
+<<https://www.itu.int/md/T01-SG12-C-0054/e>>
+- [b-ITU-T SG12 Cont47] ITU-TSG12 Study Period 2001 Contribution 47 (2002), *Rapporteur report – Workshop on Headsets/Sending Part*.  
+<<https://www.itu.int/md/T01-SG12-C-0047/e>>
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | Tariff and accounting principles and international telecommunication/ICT economic and policy issues                                                       |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                                                       |
+| Series Q        | Switching and signalling, and associated measurements and tests                                                                                           |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/P/T-REC-P.382-202303-I_PDF-E/raw.md

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+
+
+# Recommendation**ITU-T P.382 (03/2023)**
+
+SERIES P: Telephone transmission quality, telephone installations, local line networks
+
+Voice terminal characteristics
+
+---
+
+**Technical requirements and test methods for analogue wired multi-microphone headsets or headphones and corresponding universal interface of terminals**
+
+![ITU logo](0538daaa5583c23e17db3a12f2281a55_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features the letters "ITU" in a bold, blue, sans-serif font, superimposed on a stylized globe icon with intersecting lines.
+
+ITU logo
+
+## ITU-T P-SERIES RECOMMENDATIONS
+
+# TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS
+
+|                                                                                                    |                    |
+|----------------------------------------------------------------------------------------------------|--------------------|
+| Vocabulary and effects of transmission parameters on customer opinion of transmission quality      | P.10–P.19          |
+| Voice terminal characteristics                                                                     | P.30–P.39          |
+| Reference systems                                                                                  | P.40–P.49          |
+| Objective measuring apparatus                                                                      | P.50–P.59          |
+| Objective electro-acoustical measurements                                                          | P.60–P.69          |
+| Measurements related to speech loudness                                                            | P.70–P.79          |
+| Methods for objective and subjective assessment of speech quality                                  | P.80–P.89          |
+| <b>Voice terminal characteristics</b>                                                              | <b>P.300–P.399</b> |
+| Objective measuring apparatus                                                                      | P.500–P.599        |
+| Measurements related to speech loudness                                                            | P.700–P.709        |
+| Methods for objective and subjective assessment of speech and video quality                        | P.800–P.899        |
+| Audiovisual quality in multimedia services                                                         | P.900–P.999        |
+| Transmission performance and QoS aspects of IP end-points                                          | P.1000–P.1099      |
+| Communications involving vehicles                                                                  | P.1100–P.1199      |
+| Models and tools for quality assessment of streamed media                                          | P.1200–P.1299      |
+| Telemeeting assessment                                                                             | P.1300–P.1399      |
+| Statistical analysis, evaluation and reporting guidelines of quality measurements                  | P.1400–P.1499      |
+| Methods for objective and subjective assessment of quality of services other than speech and video | P.1500–P.1599      |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T P.382
+
+# Technical requirements and test methods for analogue wired multi-microphone headsets or headphones and corresponding universal interface of terminals
+
+## Summary
+
+Recommendation ITU-T P.382 specifies critical physical and electroacoustic characteristics for a universal headset interface with more than four terminals and provides corresponding test methods. Headset or headphone interfaces of diameter 3.5 mm and 2.5 mm have been widely used in digital mobile terminals during recent years. Nowadays, the consumer is free to choose either the headset or HP originally provided by the terminal manufacturer or others that are offered separately. However, the quality of service or quality of experience perceived by users is influenced by both the electrical performance of the interface and the compatibility between the terminal and the connected headset or headphone.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T P.382    | 2016-07-29 | 12          | <a href="http://handle.itu.int/11.1002/1000/12971">11.1002/1000/12971</a> |
+| 2.0     | ITU-T P.382    | 2020-10-14 | 12          | <a href="http://handle.itu.int/11.1002/1000/14466">11.1002/1000/14466</a> |
+| 3.0     | ITU-T P.382    | 2023-03-01 | 12          | <a href="http://handle.itu.int/11.1002/1000/15465">11.1002/1000/15465</a> |
+
+## Keywords
+
+Connector, headphone, headset, interface, terminals.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents/software copyrights, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2023
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                                        | Page |
+|----------------------------------------------------------------------------------------|------|
+| 1 Scope .....                                                                          | 1    |
+| 2 References.....                                                                      | 1    |
+| 3 Definitions .....                                                                    | 2    |
+| 3.1 Terms defined elsewhere .....                                                      | 2    |
+| 3.2 Terms defined in this Recommendation .....                                         | 3    |
+| 4 Abbreviations and acronyms .....                                                     | 3    |
+| 5 General description .....                                                            | 4    |
+| 6 Physical characteristics .....                                                       | 4    |
+| 6.1 General rules .....                                                                | 4    |
+| 6.2 Pin assignments .....                                                              | 4    |
+| 7 Terminal electrical interface specification.....                                     | 5    |
+| 7.1 Communication mode (terminal) .....                                                | 5    |
+| 7.2 Multimedia playback (terminal) .....                                               | 8    |
+| 7.3 Multimedia record (terminal) .....                                                 | 9    |
+| 8 Headset specification .....                                                          | 12   |
+| 8.1 Communication mode (headset).....                                                  | 12   |
+| 8.2 Multimedia playback mode (headset) .....                                           | 14   |
+| 8.3 Multimedia record mode (headset).....                                              | 14   |
+| 9 Function requirements for terminals with the universal headset interface .....       | 16   |
+| Annex A – Interpolation method for diffuse-field correction .....                      | 17   |
+| Appendix I – Audio connectivity for sockets with five contact points .....             | 18   |
+| I.1 Plug connector of diameter 2.5 mm with five poles.....                             | 18   |
+| I.2 Socket connector of diameter 2.5 mm with five contact points .....                 | 18   |
+| I.3 Plug connector of diameter 3.5 mm with five poles.....                             | 18   |
+| I.4 Socket connector of diameter 3.5 mm with five contact points .....                 | 19   |
+| Appendix II – Audio connectivity for sockets with six contact points.....              | 20   |
+| Appendix III – Audio connectivity for sockets with fewer than five contact points..... | 21   |
+| Appendix IV – Other considerations .....                                               | 22   |
+| Bibliography .....                                                                     | 23   |
+
+
+
+# Recommendation ITU-T P.382
+
+# Technical requirements and test methods for analogue wired multi-microphone headsets or headphones and corresponding universal interface of terminals
+
+# 1 Scope
+
+This Recommendation specifies electrical requirements and test methods for a multi-microphone headset or headphone (HP) interface used in digital mobile terminals. It is also applicable to terminals with a digital headset interface combined with an external adapter for an analogue (universal) headset interface. The combination is measured as one device.
+
+The principle of this Recommendation is to ensure adequate compatibility between the digital mobile terminal and the universal and multi-microphone wired analogue headset or HP, and to provide better user experience. The universal multi-microphone headset or HP interface enables the separation of sales between digital mobile terminals and headsets or HPs. One benefit is that users are free to choose their favourite type of headset or HP in the market, which in the long run will reduce E-waste.
+
+Furthermore, the universal interface can be used as the electric coupling design in hands-free systems and hearing aids for wider harmonization.
+
+To provide instructions to manufacturers and encourage them to adopt the universal headset interface, the mechanical dimensions are shown in an appendix for at least configurations with five poles.
+
+This Recommendation applies to digital mobile terminals with a physical analogue audio output and input interface that needs to support headsets with more than one microphone. Other similar information and communication technology equipment may also lie within the scope of this Recommendation.
+
+This Recommendation does not apply to terminals designed solely for digital headset or HP usage.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T P.56] Recommendation ITU-T P.56 (2011), *Objective measurement of active speech level*.
+- [ITU-T P.58] Recommendation ITU-T P.58 (2023), *Head and torso simulator for telephonometry*.
+- [ITU-T P.64] Recommendation ITU-T P.64 (2022), *Determination of sensitivity/frequency characteristics of local telephone systems*.
+- [ITU-T P.381] Recommendation ITU-T P.381 (2023), *Technical requirements and test methods for analogue wired headsets or headphones and corresponding universal interface of terminals*.
+- [ITU-T P.501] Recommendation ITU-T P.501 (2020), *Test signals for use in telephony and other speech-based applications*.
+- [IEC 60268-1] IEC 60268-1:1985, *Sound system equipment – Part1: General*.
+
+- [IEC 61260-1] IEC 61260-1:2014, *Electroacoustics – Octave-band and fractional-octave-band filters – Part I: Specifications*.
+- [EN 50332-1] CENELEC EN 50332-1:2013, *Sound system equipment: Headphones and earphones associated with personal music players – Maximum sound pressure level measurement methodology – Part 1: General method for “one package equipment”*.
+- [EN 50332-2] CENELEC EN 50332-2:2013, *Sound system equipment: Headphones and earphones associated with personal music players – Maximum sound pressure level measurement methodology – Part 2: Matching of sets with headphones if either or both are offered separately, or are offered as one package equipment but with standardised connectors between the two allowing to combine components of different manufacturers or different design*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 artificial ear** [ITU-T P.381]: A device that incorporates an acoustic coupler and a calibrated microphone for measuring sound pressure, and which has an overall acoustic impedance similar to that of the average adult ear over a given frequency band.
+
+NOTE – Definition based on that in [b-ITU-T P.10].
+
+**3.1.2 codec** [ITU-T P.381]: Combination of an analogue-to-digital encoder and a digital-to-analogue decoder operating in opposite directions of transmission in the same equipment.
+
+NOTE – This definition is based on that in [b-ITU-T G.701].
+
+**3.1.3 eardrum reference point (DRP)** [b-ITU-T P.10]: A point located at the end of the ear canal, corresponding to the eardrum position.
+
+**3.1.4 earphone** [b-IEC 60268-7]: Electroacoustic transducer by which acoustic oscillations are obtained from electric signals and intended to be closely coupled acoustically to the ear.
+
+**3.1.5 head and torso simulator (HATS) for telephonometry** [ITU-T P.381]: A manikin that extends downwards from the top of the head to the waist. It is designed to simulate the sound pick-up characteristics and the acoustic diffraction produced by the average adult, and to reproduce the acoustic field generated by the human mouth.
+
+NOTE – Definition is based on that in [b-ITU-T P.10].
+
+**3.1.6 headphone (HP)** [ITU-T P.381]: An object based on the assembly of one or two earphones on a headband or chinband, the use of which may be optional (e.g., with intra-concha earphones).
+
+NOTE – Definition based on that in [b-IEC 60268-7].
+
+**3.1.7 headset** [b-ITU-T P.10]: A device which includes telephone receiver and transmitter which is typically secured to the head or the ear of the wearer.
+
+**3.1.8 mean opinion score-listening-only quality objective (MOS-LQO)** [ITU-T P.381]: A score calculated by means of an objective model that aims to predict the quality for a listening-only test situation.
+
+NOTE 1 – Objective measurements made using the model given in [b-ITU-T P.863] give results in terms of MOS-LQO.
+
+NOTE 2 – This definition is based on that given in [b-ITU-T P.800.1].
+
+**3.1.9 mouth reference point (MRP)** [b-ITU-T P.10]: Point 25 mm in front of and on the axis of the lip plane of the artificial mouth or a typical human mouth (see Figure A.1 of [ITU-T P.64]).
+
+**3.1.10 Receive** [ITU-T P.381]: The receiving direction of the signal transmission, usually from the measurement system to the device under test.
+
+**3.1.11 Send** [ITU-T P.381]: The sending direction of the signal transmission, usually from the device under test to the measurement system.
+
+## **3.2 Terms defined in this Recommendation**
+
+None.
+
+# **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|         |                                                     |
+|---------|-----------------------------------------------------|
+| DC      | Direct Current                                      |
+| DRP     | ear Drum Reference Point                            |
+| DUT     | Device Under Test                                   |
+| EL      | Echo Loss                                           |
+| FB      | Fullband                                            |
+| FFT     | Fast Fourier Transform                              |
+| GND     | Ground                                              |
+| HATS    | Head and Torso Simulator                            |
+| HP      | Headphone                                           |
+| HTCL    | Headset Terminal Coupling Loss                      |
+| HTCLw   | weighted Headset Terminal Coupling Loss             |
+| L       | Left                                                |
+| LQO     | Listening only Quality Objective                    |
+| MIC     | Microphone                                          |
+| MIC1    | primary Microphone                                  |
+| MIC2    | secondary Microphone                                |
+| MOS-LQO | Mean Opinion Score-Listening only Quality Objective |
+| MRP     | Mouth Reference Point                               |
+| NB      | Narrowband                                          |
+| POI     | Point of Interconnection                            |
+| R       | Right                                               |
+| RMS     | Root Mean Square                                    |
+| SWB     | Super-wideband                                      |
+| TCL     | Terminal Coupling Loss                              |
+| TCLw    | weighted Terminal Coupling Loss                     |
+| THD     | Total Harmonic Distortion                           |
+| WB      | Wideband                                            |
+
+# 5 General description
+
+Generally, if a headset or HP is used, the overall user experience during a call highly depends on both the terminal and the connected headset or HP. Although the acoustic quality of the headset or HP is usually the weak link, more consideration with regard to the physical and electrical performance of the universal interface is needed.
+
+This Recommendation specifies new connection points that are compatible with the universal concentric connector interface for successful interconnection of the digital mobile terminal and the headset or HP, including the plug connector and the socket connector. Normally, the socket connector is fixed inside the terminal, with the outside rim of the socket level with the surrounding shell of the terminal.
+
+# 6 Physical characteristics
+
+## 6.1 General rules
+
+Two types of concentric socket connectors of different diameters are recommended for use: 2.5 mm; and 3.5 mm. An isometric view of the plug and socket connectors is shown in Figure 6-1 of [ITU-T P.381].
+
+If the terminal is equipped with a headset interface designed for both communication and audio playback and this multi-microphone interface is utilized, the fixed connector shall be a 3.5 mm diameter or 2.5 mm diameter concentric socket connector. Detailed dimensions for socket and the plug connectors with more than four contact points are given in Appendices I to III. Some terminals with curved edges may not work well with the dimensions given in Appendices I to III.
+
+NOTE – The contact points here do not include special points reserved for other functions.
+
+## 6.2 Pin assignments
+
+This clause gives an illustration of pin assignments of the socket connector with five contact points and those of the mated plug, as shown in Figure 1.
+
+![Diagram of a socket connector with five contact points showing pin assignments and plug details.](b0211cee4b20034939d883ac0d70f696_img.jpg)
+
+The diagram illustrates the pin assignments for a socket connector with five contact points. On the left, five pins are shown with their respective electrical connections: pin 4 is connected to the top terminal, pin 6 to the second terminal, pin 2 to the third terminal, pin 1 to the fourth terminal, and pins 3 and 5 are connected to the bottom terminal. On the right, a cross-sectional view of a plug is shown, detailing its components: Tip, Ring 1, Alternative Ring 2, Ring 3, and Sleeve isolation. The diagram is labeled P.382(16)\_F01.
+
+Diagram of a socket connector with five contact points showing pin assignments and plug details.
+
+**Figure 1 – Pin assignments of a socket connector with five contact points**
+
+The physical pinout order of the universal interface is important and should coordinate with the connected headset or HP.
+
+A socket connector with five contact points shall be compatible with both the three pole and four pole plugs specified in [ITU-T P.381].
+
+It is recommended that terminals be able to identify different plugs intelligently and automatically.
+
+It is recommended that a normally open switch be used on the socket connector to detect when the plug is fully inserted.
+
+### 6.2.1 Recommended pin assignment
+
+Point 1 of the socket is to be connected to the tip of the plug, linking it to the left (L) audio channel of the receiver. Point 2 is to be connected to ring 2, linking it to the transducer secondary microphone+ (MIC2+) (right (R) recording channel) of the device under test (DUT). Point 3 is to be connected to ring 1, linking it to the R audio channel of the receiver. Points 4 and 5 are to be connected to the sleeve, linking it to ground (GND). Point 6 is to be connected to ring 3, linking it to the transducer primary microphone+ (MIC1+) (L recording channel) of the DUT.
+
+Referring to Figure 1:
+
+- 1 is the contact point of the tip, linking it to the L channel of the receiver (HP L audio);
+- 2 is the contact point of ring 2, linking it to the transducer (MIC2+);
+- 3 is the contact point of ring 1, linking it to the R channel of the receiver (HP R audio);
+- 4 is the contact point of the sleeve, linking it to the GND;
+- 5 is the bushing of the socket, linking it to the GND when it is made of conductive material;
+- 6 is the contact point of ring 3, linking it to the transducer (MIC1+).
+
+In summary, the pole order from the tip to the sleeve of the headset plug is HP L/MIC2/HP R/MIC1/GND.
+
+The pinout order of HP L/MIC2/HP R/MIC1/GND has the advantage of electrostatic discharge protection and allows for both plastic and metallic converters.
+
+### 6.2.2 Alternative pin assignment
+
+Referring to Figure 1:
+
+- 1 is the contact point of the tip, linking it to the L channel of the receiver (HP L audio);
+- 2 is the contact point of ring 1, linking it to the R channel of the receiver (HP R audio);
+- 3 is the contact point of ring 2, linking it to the transducer (MIC2+);
+- 4 is the contact point of the sleeve, linking it to the transducer (MIC1+);
+- 5 is the bushing of the socket, linking it to the transducer (MIC1+);
+- 6 is the contact point of ring 3, linking it to GND when it is made of conductive material.
+
+In summary, the alternative pole order from the tip to the sleeve of the headset plug is: HP L/HP R/MIC2/GND/MIC1.
+
+# 7 Terminal electrical interface specification
+
+## 7.1 Communication mode (terminal)
+
+Test set-ups and requirements in this mode are harmonized with the existing [ITU-T P.381] specification, so only the general test set-up is repeated here. See [ITU-T P.381] for requirements and specific test set-ups.
+
+### 7.1.1 Test set-up for the communication mode (terminal)
+
+Test set-ups are shown in Figures 7-1 and 7-2 of [ITU-T P.381].
+
+#### 7.1.1.1 Input and output characteristics of the test system for connection to the headset connector
+
+The output of the test system connected to the interface in Send of the headset connector must be direct current (DC) resistant. The output impedance shall be between 1  $\Omega$  and 10 k $\Omega$ . The dynamic range of the test system shall be consistent with (or exceed) the level range provided by headset MICs.
+
+The input of the test system connected to the receiving interfaces of the headset connectors shall have an input impedance of 32  $\Omega$ . The dynamic range shall be consistent with (or exceed) the output level range provided by the electrical output of the digital mobile terminal headset outputs.
+
+The common GND impedance (between sending and receiving sides) for the test system shall be  $\leq 0.05 \Omega$ .
+
+#### 7.1.1.2 Test signals and test signal levels
+
+If not specified otherwise, fullband (FB) real speech signals specified in [ITU-T P.501] are used for the measurements. Detailed information about the test signal used is specified in the corresponding clause of this Recommendation.
+
+All test signals used in Receive tests have to be band limited with  $\geq 24$  dB/octave roll off, achieved by bandpass filter. The signal should be band limited between:
+
+- in narrowband (NB) mode, 100 Hz and 4 kHz;
+- in wideband (WB) mode, 100 Hz and 8 kHz;
+- in super-wideband (SWB) mode, 50 Hz and 16 kHz;
+- in FB mode, 20 Hz and 20 kHz.
+
+For real speech, the test signal levels are in accordance with the ITU-T P.56 active speech level of the (band limited in receiving direction) test signal, calculated over the complete test sequence, if not specified otherwise. Other test signal levels are calculated as the average level over the complete test sequence length of the test signals. For the receiving direction, the signal should be band limited.
+
+If not stated otherwise, the nominal average signal levels for the measurements are as follows:
+
+- $-16$  dBm0 (absolute signal power level, in decibels, relative to a point of zero relative level) in Receive;
+- $-60$  dBV (decibels relative to 1 V) in Send [typical equivalent signal level of a microphone (MIC) of the DUT corresponding to  $-4.7$  dBPa (decibels at 1 Pa) at the mouth reference point (MRP)];
+- the Receive volume control is adjusted to the setting that produces the level closest to  $-39$  dBV when considering binaural headsets.
+
+NOTE – If different network signal levels are used, it should be noted and stated in the test. The Lombard effect (increased talker speech level due to high background noise) is considered in the background noise tests.
+
+Some tests require exact synchronization of test signals in the time domain. Therefore, it is necessary to take the delays of the terminals into account. When analysing signals, any delays introduced by the test system, codecs and terminals have to be taken into account accordingly.
+
+Test set-ups and requirements in this mode are harmonized with the existing ITU-T P.381 specification.
+
+### 7.1.2 Delay for the communication mode (terminal)
+
+The detailed requirements are specified in clause 7.1.2.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.2.2 of [ITU-T P.381].
+
+### 7.1.3 Level in Send for nominal speech input level for the communication mode (terminal)
+
+The detailed requirements are specified in clause 7.1.3.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.3.2 of [ITU-T P.381].
+
+### 7.1.4 Level in Receive for nominal speech input level
+
+The detailed requirements are specified in clause 7.1.4.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.4.2 of [ITU-T P.381].
+
+### **7.1.5 Level in Send for low and high speech input levels for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.5.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.5.2 of [ITU-T P.381].
+
+### **7.1.6 Linearity in Receive for the communication mode (terminal)**
+
+The linearity in Receive is for further study
+
+### **7.1.7 Sending frequency response for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.7.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.7.2 of [ITU-T P.381].
+
+### **7.1.8 Receiving frequency response for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.8.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.8.2 of [ITU-T P.381].
+
+### **7.1.9 Sidetone loss for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.9.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.9.2 of [ITU-T P.381].
+
+### **7.1.10 Sidetone delay for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.10.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.10.2 of [ITU-T P.381].
+
+### **7.1.11 Noise in Send for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.11.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.11.2 of [ITU-T P.381].
+
+### **7.1.12 Noise in Receive for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.12.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.12.2 of [ITU-T P.381].
+
+### **7.1.13 Sending distortion for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.13.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.13.2 of [ITU-T P.381].
+
+### **7.1.14 Receive distortion for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.14.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.14.2 of [ITU-T P.381].
+
+### **7.1.15 Noise cancellation test in Send for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.15.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.15.2 of [ITU-T P.381].
+
+### **7.1.16 One-way speech quality in Send for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.16.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.16.2 of [ITU-T P.381].
+
+### **7.1.17 One-way speech quality in Receive for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.17.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.17.2 of [ITU-T P.381].
+
+### **7.1.18 Terminal coupling loss for the communication mode (terminal)**
+
+The detailed requirements for weighted terminal coupling loss (TCLw) and terminal coupling loss (TCL) are specified in clause 7.1.18.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.18.2 of [ITU-T P.381].
+
+### **7.1.19 Temporal echo effects for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.19.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.19.2 of [ITU-T P.381].
+
+### **7.1.20 Double talk performance for the communication mode (terminal)**
+
+#### **7.1.20.1 Attenuation range in Send during double talk, $A_{H,s,dt}$**
+
+The detailed requirements are specified in clause 7.1.20.1.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.20.1.2 of [ITU-T P.381].
+
+#### **7.1.20.2 Attenuation range in Receive during double talk, $A_{H,r,dt}$**
+
+The detailed requirements are specified in clause 7.1.20.2.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.20.2.2 of [ITU-T P.381].
+
+#### **7.1.20.3 Detection of echo components during double talk**
+
+The detailed requirements are specified in clause 7.1.20.3.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.20.3.2 of [ITU-T P.381].
+
+### **7.1.21 Activation in Send for the communication mode (terminal)**
+
+The detailed requirements are specified in clause 7.1.21.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.1.21.2 of [ITU-T P.381].
+
+## **7.2 Multimedia playback (terminal)**
+
+Test set-ups and requirements in this mode are harmonized with the existing [ITU-T P.381] specification.
+
+### **7.2.1 Test set-up for the multimedia playback mode (terminal)**
+
+General test set-ups are described in clause 7.2.1 of [ITU-T P.381].
+
+### **7.2.2 Output level for the multimedia playback mode (terminal)**
+
+The detailed requirements are specified in clause 7.2.2.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.2.2.2 of [ITU-T P.381].
+
+### **7.2.3 Frequency response for the multimedia playback mode (terminal)**
+
+The detailed requirements are specified in clause 7.2.3.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.2.3.2 of [ITU-T P.381].
+
+### 7.2.4 Noise for the multimedia playback mode (terminal)
+
+The detailed requirements are specified in clause 7.2.4.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.2.4.2 of [ITU-T P.381].
+
+### 7.2.5 Distortion for the multimedia playback mode (terminal)
+
+The detailed requirements are specified in clause 7.2.5.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.2.5.2 of [ITU-T P.381].
+
+### 7.2.6 Receiving crosstalk for the multimedia playback mode (terminal)
+
+The detailed requirements are specified in clause 7.2.6.1 of [ITU-T P.381].
+
+The test details are specified in clause 7.2.6.2 of [ITU-T P.381].
+
+## 7.3 Multimedia record (terminal)
+
+### 7.3.1 Test set-up for the multimedia record mode (terminal)
+
+The test set-up is shown in Figure 2.
+
+![Figure 2: Set-up for testing the electrical headset interface. The diagram shows a 'Wireless digital terminal' containing 'Headset signal processing', 'Audio recorder', and 'Signal storage'. This terminal is connected to a 'Test system' via 'Left/right channel' lines. The 'Test system' is also connected to 'Signal storage, e.g., memory card' via 'Left/right channel' lines. The 'Test system' is represented by a box with a sine wave symbol and a variable resistor symbol.](18722c46c9e8475524e634dedd08bac2_img.jpg)
+
+Figure 2: Set-up for testing the electrical headset interface. The diagram shows a 'Wireless digital terminal' containing 'Headset signal processing', 'Audio recorder', and 'Signal storage'. This terminal is connected to a 'Test system' via 'Left/right channel' lines. The 'Test system' is also connected to 'Signal storage, e.g., memory card' via 'Left/right channel' lines. The 'Test system' is represented by a box with a sine wave symbol and a variable resistor symbol.
+
+P.382(16)\_F02
+
+Figure 2 – Set-up for testing the electrical headset interface
+
+#### 7.3.1.1 Input and output characteristics of the test system for connecting to the headset connector
+
+The output of the test system connected to the sending interface of the headset connector must be DC resistant. The output impedance shall be between 1 Ω and 10 kΩ. The dynamic range shall be consistent with (or exceed) the level range provided by headset MICs.
+
+The input of the test system connected to the Receive interfaces of the headset connectors shall have an input impedance of 32 Ω. The dynamic range shall be consistent with (or exceed) the output level range provided by the electrical output of the digital mobile terminal headset outputs.
+
+#### 7.3.1.2 Test signals and test signal levels
+
+All input signal levels are expressed in decibels relative to 1 V, as they are electrically output from the test system into each device headset socket MIC input channel.
+
+All output signal levels specified in this clause are relative to decibels relative to full scale, where 0 dBFS represents the root mean square (RMS) level of a full-scale sinusoidal signal.
+
+Programme simulation noise as specified in [IEC 60268-1] is used for the measurements. Detailed information about the test signal used is specified in the corresponding clause of this Recommendation.
+
+The programme simulation noise according to [EN 50332-1] and [EN 50332-2] is band limited by design and requires no filtering.
+
+All test signal levels are relative to the average level over the complete test sequence length of the test signals, if not specified otherwise.
+
+Some tests require exact synchronization of test signals in the time domain. Therefore, it is necessary to take the delays of the terminals into account. When analysing signals, any delays introduced by the test system, codecs and terminals have to be taken into account accordingly.
+
+### **7.3.2 Input level for the multimedia record mode (terminal)**
+
+#### **7.3.2.1 Requirement**
+
+The level is measured as the digital input level generated by the output stereo file of the mobile terminal recorder when applying a stereo signal to the headset interface.
+
+The input level shall be  $-29.0 \text{ dBFS} \pm 3 \text{ dB}$  when playing programme simulation noise at  $-60 \text{ dBV}$  at the mobile terminal inputs.
+
+For a stereo recording, the offset between L and R channel shall be  $< 1 \text{ dB}$ .
+
+#### **7.3.2.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be programme simulation noise providing sufficient signal energy to 22 kHz. The test signal level is  $-60 \text{ dBV}$ .
+- 3) For the calculation, the averaged level of the encoded file in the signal storage is used. The output level is determined up to 22 kHz.
+- 4) The output level is expressed in decibels relative to full scale.
+
+### **7.3.3 Frequency response for the multimedia record mode (terminal)**
+
+#### **7.3.3.1 Requirement**
+
+The frequency response is evaluated from a digital output file of the mobile terminal recorder when applying a signal to the headset interface.
+
+The frequency response shall be within  $\pm 2 \text{ dB}$  between 500 Hz and 18 kHz when programme simulation noise at  $-60 \text{ dBV}$  is electrically presented at the mobile terminal inputs. The requirement applies to each stereo channel individually.
+
+#### **7.3.3.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be programme simulation noise providing sufficient signal energy to 22 kHz. The test signal level is  $-60 \text{ dBV}$ .
+- 3) The sending frequency response is determined in one-12th octave bands, as given in [IEC 61260-1] for frequencies from 100 Hz to 18 kHz inclusive, measured at the point of interconnection (POI). In each one-12th octave band, the power density spectrum of the measured signal is compared to that of the input signal averaged over the complete test sequence length.
+- 4) The sensitivity is expressed in decibels relative to full scale per decibel relative to 1 V.
+
+#### **7.3.4 Acoustic input range for the multimedia record mode (terminal)**
+
+#### **7.3.4.1 Requirement**
+
+The acoustic input range is evaluated from a digital stereo output file of the mobile terminal recorder when applying a signal to the headset interface.
+
+The input range shall be 50 dB when playing programme simulation noise at  $-40 \text{ dBV}$  and at  $-90 \text{ dBV}$  at the mobile terminal inputs.
+
+#### **7.3.4.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be programme simulation noise. The test signal levels are  $-40.0$  dBV and  $-90.0$  dBV.
+- 3) The recorded files are compared to the input and no temporal clipping should be observed for either input level.
+- 4) The acoustic input range is expressed in decibels.
+
+### **7.3.5 Phase response for the multimedia record mode (terminal)**
+
+#### **7.3.5.1 Requirement**
+
+The phase response is evaluated from a digital stereo output file of the mobile terminal recorder when applying a stereo signal to the headset interface.
+
+The phase response shall be in phase, as confirmed by the transfer function, when programme simulation noise at  $-60$  dBV is electrically presented at the mobile terminal inputs.
+
+#### **7.3.5.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be programme simulation noise. The test signal level is  $-60.0$  dBV.
+- 3) The recorded file is compared to the input and the channel specific transfer functions individually computed.
+- 4) The output L and R responses are compared to one another.
+
+### **7.3.6 Distortion at maximum acoustic input in multimedia record mode**
+
+#### **7.3.6.1 Requirement**
+
+The total harmonic distortion (THD) is evaluated from a digital output file of the mobile terminal recorder when applying a signal to the headset interface.
+
+The THD + noise shall be at least 30 dB between the signal level in the frequency range between 50 Hz and 18 kHz when a sinusoidal signal at  $-40.0$  dBV is electrically presented at the mobile terminal inputs.
+
+#### **7.3.6.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be a sinusoidal signal at 50 Hz and 1 kHz. The test signal level is  $-40.0$  dBV and the duration shall be  $<1$  s. A short activation and conditioning sequence of male or female ITU-T P.501 speech may be needed, in which case it shall be input prior to the sinusoidal signal at the nominal signal level.
+- 3) The spectral distribution of the recorded file is analysed with a 4k-point fast Fourier transform (FFT), and the THD + noise is computed using a flat top window.
+- 4) The output distortion response is expressed in decibels.
+
+### **7.3.7 Cross-talk for the multimedia record mode (terminal)**
+
+#### **7.3.7.1 Requirement**
+
+The cross-talk is evaluated from a digital stereo output file of the mobile terminal recorder when applying a stereo signal to the headset interface.
+
+The cross-talk shall be below 50 dB, as confirmed by the transfer function, when programme simulation noise at  $-40$  dBV is electrically presented at the mobile terminal inputs.
+
+#### **7.3.7.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be programme simulation noise. The test signal level is  $-40.0$  dBV.
+- 3) The recorded file is compared to the input and the channel specific transfer functions individually computed.
+- 4) The cross-talk is calculated between MIC1 and MIC2, as well as vice versa, MIC2 versus MIC1.
+
+### **7.3.8 Time offset and sampling accuracy for the multimedia record mode (terminal)**
+
+#### **7.3.8.1 Requirement**
+
+The time offset is evaluated from a digital stereo output file of the mobile terminal recorder when applying a stereo signal to the headset interface.
+
+The recorded file's sinusoidal frequency shall deviate by  $<0.1\%$ , when the input sinusoidal 1 kHz signal at  $-60$  dBV is electrically presented at the mobile terminal inputs.
+
+#### **7.3.8.2 Test**
+
+- 1) The test set-up is according to Figure 2.
+- 2) The test signal used for the measurements shall be a 1 kHz sinusoidal signal. The test signal level is  $-60.0$  dBV.
+- 3) The recorded file is compared to the input and the transfer function computed. The spectral distribution of the output signal is analysed with a 4k-point FFT and the windowing used is the flat top window.
+- 4) The output L and R responses are individually computed.
+
+# **8 Headset specification**
+
+## **8.1 Communication mode (headset)**
+
+Test set-ups and requirements in this mode are mostly harmonized with the existing ITU-T P.381 specification, except for clause 8.1.7, which, due to the multiple MICs, needs a specific test.
+
+### **8.1.1 Test set-up (headset)**
+
+The test set-up is specified in clause 8.1.1 of [ITU-T P.381].
+
+### **8.1.2 Sensitivity in Send (headset)**
+
+The detailed requirements are specified in clause 8.1.2.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.2.2 of [ITU-T P.381].
+
+### **8.1.3 Sensitivity in Receive (headset)**
+
+The detailed requirements are specified in clause 8.1.3.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.3.2 of [ITU-T P.381].
+
+### **8.1.4 Sending frequency response (headset)**
+
+The detailed requirements are specified in clause 8.1.4.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.4.2 of [ITU-T P.381].
+
+### 8.1.5 Receiving frequency response (headset)
+
+The detailed requirements are specified in clause 8.1.5.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.5.2 of [ITU-T P.381].
+
+### 8.1.6 Idle channel noise in Send (headset)
+
+The detailed requirements are specified in clause 8.1.6.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.6.2 of [ITU-T P.381].
+
+### 8.1.7 Distortion in Send (headset)
+
+The detailed requirements are specified in clause 8.1.7.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.1.7.2 of [ITU-T P.381].
+
+### 8.1.8 Headset terminal coupling loss (headset)
+
+#### 8.1.8.1 Requirement
+
+For speech transmission, the weighted headset terminal coupling loss (HTCLw) for NB, and headset terminal coupling loss (HTCL) for WB, SWB and FB is evaluated for the electrical interface MIC1 or MIC2 lines when applying a stereo signal to the electrical receiver of the headset interface.
+
+The coupling loss shall be <65 dB, as confirmed by each transfer function, when programme simulation noise at -22 dBV is electrically presented at the mobile terminal inputs.
+
+#### 8.1.8.2 Test
+
+- 1) The test set-up is according to Figure 3.
+- 2) The test signal used for the measurements shall be programme simulation noise. The test signal level is -22.0 dBV.
+- 3) The headset MIC output is compared to the headset receiver input and the channel specific transfer functions are individually computed in the frequency range between 50 Hz and 18 kHz.
+- 4) The coupling loss is calculated between HP L input and MIC1 output, as well as HP R input and MIC2 output, respectively. Coupling loss between HP L input and MIC2 output, as well as HP R Input and MIC1 output, should be confirmed to also comply with the requirement.
+- 5) For NB mode, HTCLw is calculated according to clause B.4 of [ITU-T G.122] (trapezoidal rule). In WB, SWB and FB mode, HTCL is calculated as the echo loss (EL) from 50 Hz to 18 kHz. For the calculation, the averaged test signal level at each frequency band takes as reference the averaged measured echo signal level in each frequency band. For the measurement, a time window has to be applied that is adapted to the duration of the actual test signal. The EL is calculated by the following equations. The form of the first is generalized from that specified in clause B.4 of [ITU-T G.122] to calculate EL based on tabulated data, which allows the calculation of EL within any frequency range between  $f_0$  and  $f_N$ .
+
+$$L_e = C - 10 \log_{10} \sum_{i=1}^N (A_i + A_{i-1})(\log_{10} f_i - \log_{10} f_{i-1}),$$
+
+where  $C = 10 \log_{10} 2 (\log_{10} f_N - \log_{10} f_0)$ ,
+
+where
+
+$A_0$  is the output/input power ratio at frequency  $f_0 = 50$  Hz;
+
+$A_1$  is the output/input power ratio at frequency  $f_i$ ;
+
+$A_N$  is the output/input power ratio at frequency  $f_N = 18$  kHz
+
+## 8.2 Multimedia playback mode (headset)
+
+Test set-ups and requirements in this mode are harmonized with the existing ITU-T P.381 specification.
+
+### 8.2.1 Test set-up (headset)
+
+The test set-up is specified in clause 8.2.1 of [ITU-T P.381].
+
+### 8.2.2 Sensitivity for the multimedia playback mode (headset)
+
+The detailed requirements are specified in clause 8.2.2.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.2.2.2 of [ITU-T P.381].
+
+### 8.2.3 Distortion for the multimedia playback mode (headset)
+
+The detailed requirements are specified in clause 8.2.3.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.2.3.2 of [ITU-T P.381].
+
+### 8.2.4 Receiving crosstalk for the multimedia playback mode (headset)
+
+The detailed requirements are specified in clause 8.2.4.1 of [ITU-T P.381].
+
+The test details are specified in clause 8.2.4.2 of [ITU-T P.381].
+
+## 8.3 Multimedia record mode (headset)
+
+### 8.3.1 Test set-up (headset)
+
+The test set-up is shown in Figure 3.
+
+![Figure 3: Set-up for testing the headset. The diagram shows a headset with a microphone and earpiece connected to a 'Headset reference interface' box. This box is connected to a 'Test system' box. The test system has two output sources, one labeled -90° and the other 90°. The -90° source is connected to the earpiece, and the 90° source is connected to the microphone. A dashed circle with arrows indicates the acoustic path from the earpiece to the microphone, with a distance 'd' marked between them. The test system also has two input sources, one labeled -90° and the other 90°. The diagram is labeled P.382(16)_F03.](492256bb98eb10f95553a7b1983c4b96_img.jpg)
+
+The diagram illustrates the test set-up for a headset. A headset is shown with a microphone and an earpiece. The microphone is connected to a 'Headset reference interface' box, which is in turn connected to a 'Test system' box. The test system has two output sources, one labeled  $-90^\circ$  and the other  $90^\circ$ . The  $-90^\circ$  source is connected to the earpiece, and the  $90^\circ$  source is connected to the microphone. A dashed circle with arrows indicates the acoustic path from the earpiece to the microphone, with a distance  $d$  marked between them. The test system also has two input sources, one labeled  $-90^\circ$  and the other  $90^\circ$ . The diagram is labeled P.382(16)\_F03.
+
+Figure 3: Set-up for testing the headset. The diagram shows a headset with a microphone and earpiece connected to a 'Headset reference interface' box. This box is connected to a 'Test system' box. The test system has two output sources, one labeled -90° and the other 90°. The -90° source is connected to the earpiece, and the 90° source is connected to the microphone. A dashed circle with arrows indicates the acoustic path from the earpiece to the microphone, with a distance 'd' marked between them. The test system also has two input sources, one labeled -90° and the other 90°. The diagram is labeled P.382(16)\_F03.
+
+Figure 3 – Set-up for testing the headset
+
+Requirements for HATS and ear simulators are specified in clause 8.2.1 of [ITU-T P.381].
+
+#### 8.3.1.1 Input and output characteristics of the test system for connecting the headset
+
+The output impedance shall be  $< 2\ \Omega$ . The RMS output voltage shall be adjusted not to overdrive an artificial mouth or loudspeaker adjacent to the HATS. The common GND impedance (between sending and receiving sides) for the test system shall be  $\leq 0.05\ \Omega$ .
+
+#### 8.3.1.2 Test signals and test signal levels
+
+Sinusoidal signals are used, and signals analysed in one-12th octave bands.
+
+All test signal levels are referred to the average level of the test signals, averaged over the complete test sequence length, if not described otherwise.
+
+The nominal average signal level for the measurements is  $-28.7$  dBPa at the MRP.
+
+Some tests require exact synchronization of test signals in the time domain. Therefore, it is necessary to take the delays of the terminals into account. When analysing signals, any delays introduced by the test system, codecs and terminals have to be taken into account accordingly.
+
+#### 8.3.1.3 Positioning of the headsets
+
+The same guidelines and requirements on headset positioning apply as in clause 8.1.1.3 of [ITU-T P.381].
+
+#### 8.3.1.4 Position and calibration of reference loudspeaker
+
+The reference loudspeaker or mouth shall be calibrated and equalized at the appropriate distance for each test case. The calibration and equalization shall be performed using a free field microphone and is analysed in one-12th octave bands. During equalization, the HATS is removed from the sound field.
+
+### 8.3.2 Frequency response for the multimedia record mode (headset)
+
+#### 8.3.2.1 Requirement
+
+The frequency response is evaluated from the stereo signal of the headset reference interface when reproducing a mono signal at the output of the reference loudspeaker. A reference microphone is placed close to the MIC under test and this reference measurement is used to evaluate the frequency response.
+
+The frequency response shall be inside the mask in Table 1 for each stereo channel individually when sinusoidal signals at  $-28.7$  dBPa are acoustically output from the reference loudspeaker. The requirement is only applicable for  $0^\circ$  incidence.
+
+**Table 1**
+
+| Frequency (Hz) | Upper limit (dB) | Lower limit (dB) |
+|----------------|------------------|------------------|
+| 200            | 5                | -5               |
+| 5 000          | 5                | -5               |
+| 14 000         | 0                | -20              |
+
+NOTE 1 – All sensitivity values are expressed in decibels on an arbitrary scale.
+
+NOTE 2 – The limits for intermediate frequencies lie on a straight line drawn between the given values on a logarithmic (frequency) – linear (decibel) scale.
+
+#### 8.3.2.2 Test
+
+- 1) The test set-up is according to Figure 3. The reference loudspeaker is placed at  $d = 50$  cm distance from the HATS MRP. A reference microphone is placed close to the MIC under test.
+- 2) The headset is mounted on the HATS, which is rotated from  $-90^\circ$  to  $90^\circ$  in steps of  $45^\circ$  and the MIC electrical signals are picked up by the test system.
+- 3) For the test, sinusoidal signals are used in the bandwidth between 200 Hz and 14 kHz. The duration of each sine wave shall be  $< 1$  s. The signals are played over the free-standing loudspeaker or artificial mouth at  $-28.7$  dBPa, measured at the HATS MRP.
+- 4) The sending frequency response is analysed with a 4k-point FFT and determined in one-12th octave bands, as given in [IEC 61260-1] for frequencies from 200 Hz to 14 kHz inclusive, measured at the POI. In each one-12th octave band, the power density spectrum of the
+
+measured signal is compared to the power density spectrum of the input signal using a flat top window, and averaged over the complete test sequence length.
+
+### **8.3.3 Maximum acoustic input for the multimedia record mode (headset)**
+
+#### **8.3.3.1 Requirement**
+
+The maximum acoustic input is evaluated from the individual L and R signals of the headset reference interface when reproducing a mono signal at the output of the reference loudspeaker.
+
+The maximum acoustic input shall be linear in level to the programme simulation noise signal, as the levels 0 dBPa and +16 dBPa are acoustically output from the reference loudspeaker.
+
+#### **8.3.3.2 Test**
+
+- 1) The test set-up is according to Figure 3. The reference loudspeaker is placed at  $d = 10$  cm distance from the HATS MRP, then the HATS is rotated 90° L and R, respectively, so each headset MIC is measured in front of the reference loudspeaker.
+- 2) Programme simulation noise as specified in [IEC 60268-1] is used for the measurements. Detailed information about the test signal used is specified in the corresponding clause of this Recommendation. The programme simulation noise according to [EN 50332-1] and [EN 50332-2] is band limited by design and requires no filtering.
+- 3) The test levels are 0 dBPa and +16 dBPa, as measured at the headset MIC location.
+- 4) The electrical MIC output signal is analysed with a 4k-point FFT, and the transfer function referenced to the acoustic spectral density and computed using a flat top window.
+
+### **8.3.4 Distortion at maximum acoustic input for the multimedia record mode (headset)**
+
+#### **8.3.4.1 Requirement**
+
+The distortion at maximum acoustic input is evaluated from the individual L and R signals of the headset reference interface when reproducing a mono signal at the output of the reference loudspeaker.
+
+The THD + noise shall be <30 dB, as sinusoidal signals at level +20.7 dBPa are acoustically output from the reference loudspeaker.
+
+#### **8.3.4.2 Test**
+
+- 1) The test set-up is according to Figure 3. The reference loudspeaker is placed at 10 cm distance from the HATS MRP, then the HATS is rotated 90° L and R, respectively, so that each headset MIC is measured in front of the reference loudspeaker.
+- 2) For the test, a sinusoidal signal at frequencies of 315 Hz and 1 000 Hz is used. The duration of the sine wave shall be <1 s. The sinusoidal signal levels shall be 20.7 dBPa at the ear reference point.
+- 3) The signal to harmonic distortion ratio is measured selectively up to 10 kHz.
+
+# **9 Function requirements for terminals with the universal headset interface**
+
+See clause 9 of [ITU-T P.381] for functional requirements and impedance ranges for the terminals that should be supported.
+
+# Annex A
+
+## **Interpolation method for diffuse-field correction**
+
+(This annex forms an integral part of this Recommendation.)
+
+For measurements requiring diffuse-field correction values for closer frequency spacing than one-12th octave bands, linear interpolation on a logarithmic scale from one-12th octave band interpolated values in Table 14b of [ITU-T P.58] shall be used.
+
+## Appendix I
+
+### Audio connectivity for sockets with five contact points
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This appendix illustrates the dimensions of concentric plug and socket connectors with five contact points.
+
+### I.1 Plug connector of diameter 2.5 mm with five poles
+
+The 2.5 mm diameter plug connector with five poles is for further study.
+
+### I.2 Socket connector of diameter 2.5 mm with five contact points
+
+The 2.5 mm diameter socket connector with five poles is for further study.
+
+### I.3 Plug connector of diameter 3.5 mm with five poles
+
+Figure I.1 shows the shape and dimensions of the 3.5 mm diameter plug connector with five poles. The width of strip A along the axial direction is 0.15 mm and shall be free of sharp edges at its corners. Junctions B should be free of burr or flash.
+
+NOTE – "Flash" here refers to a rough edge or ridge on the surface.
+
+![Figure I.1: Shape and dimensions of the 3.5 mm diameter plug connector with five poles. The diagram shows a cross-section of the connector with various dimensions and callouts. Dimensions include 14.0, 8.5, 4.8, 0.7, 2.4 Max, 3.0±0.05, 2.9±0.05, 3.1±0.05, 3.4±0.05, 3.5±0.05, and R0.25. Callouts include (1) tip made of conductive material, (2) insulating rings, (3) ring 1 made of conductive material, (4) available spaces for a conductive ring 2, (5) ring 3 made of conductive material, (6) sleeve made of conductive material, and (7) illustration of the hand grip at the end of a plug. Asterisks (*) indicate dimensions to be found in ITU-T P.381. A general tolerance of ± 0.2 is specified for dimensions without individual tolerances.](8db6897b1527256adb62e789ab3e5197_img.jpg)
+
+Figure I.1: Shape and dimensions of the 3.5 mm diameter plug connector with five poles. The diagram shows a cross-section of the connector with various dimensions and callouts. Dimensions include 14.0, 8.5, 4.8, 0.7, 2.4 Max, 3.0±0.05, 2.9±0.05, 3.1±0.05, 3.4±0.05, 3.5±0.05, and R0.25. Callouts include (1) tip made of conductive material, (2) insulating rings, (3) ring 1 made of conductive material, (4) available spaces for a conductive ring 2, (5) ring 3 made of conductive material, (6) sleeve made of conductive material, and (7) illustration of the hand grip at the end of a plug. Asterisks (\*) indicate dimensions to be found in ITU-T P.381. A general tolerance of ± 0.2 is specified for dimensions without individual tolerances.
+
+- |                                                      |                                            |
+|------------------------------------------------------|--------------------------------------------|
+| ① tip made of conductive material                    | ② insulating rings                         |
+| ③ ring 1 made of conductive material                 | ④ available spaces for a conductive ring 2 |
+| ⑤ ring 3 made of conductive material                 | ⑥ sleeve made of conductive material       |
+| ⑦ illustration of the hand grip at the end of a plug |                                            |
+
+\*Dimensions intentionally left out, refer to drawings in [ITU-T P.381] for dimensional guidelines.
+
+**Figure I.1 – Shape and dimensions of the 3.5 mm diameter plug connector with five poles**
+
+The grip dimensions of the five pole connector shall be harmonized with the ITU-T P.381 dimensions for optimum compatibility.
+
+### I.4 Socket connector of diameter 3.5 mm with five contact points
+
+The socket should be able to mate and cooperate with the plug reliably. The dimensions (see Table I.1) and the positioning for each contact spring are illustrated in Figure I.2. Considering the tolerance of the plug dimension and positioning of the socket contact spring, in addition to the shift of the practical contact point location caused by the width of the spring, the minimum distance between the contact point of the ring 2 spring and that of the sleeve spring is recommended to be more than 2.4 mm. If bushing of the socket is made of conductive material, the contact area of the sleeve spring may exceed the given range indicated in Figure I.2, so bushing of the socket should not be longer than 2.4 mm.
+
+**Table I.1 – Specific spring contact dimensions for five contact points**
+
+| Dimension | Five pole socket: length (mm) |
+|-----------|-------------------------------|
+| Tip       | 11.95                         |
+| Ring 1    | 7.6                           |
+| Ring 2    | Not defined                   |
+| Ring3     | 3.7                           |
+| Sleeve    | 1.0                           |
+
+NOTE – Entries shall be contact dimensions with a plug inserted
+
+![Figure I.2: Dimensions of the 3.5 mm diameter socket with five contact points and positioning of each contact spring. The diagram shows a cross-section of the socket with five contact springs: Sleeve spring, Ring 3 spring, Ring 1 spring, Tip spring, and Ring 2 spring. The bushing of the socket is shown at the bottom. Dimensions are indicated by arrows and labels: Ring 1 ±0.2, Ring 3 ±0.2, Sleeve ±0.5, Ø 3.6±0.04, Ring 2 ±0.2, and Tip +0.3/-0.2. The diagram is labeled P.382(16)_FI.2.](cb74fd9f5ec715dd3e2e325b864b48bc_img.jpg)
+
+Figure I.2: Dimensions of the 3.5 mm diameter socket with five contact points and positioning of each contact spring. The diagram shows a cross-section of the socket with five contact springs: Sleeve spring, Ring 3 spring, Ring 1 spring, Tip spring, and Ring 2 spring. The bushing of the socket is shown at the bottom. Dimensions are indicated by arrows and labels: Ring 1 ±0.2, Ring 3 ±0.2, Sleeve ±0.5, Ø 3.6±0.04, Ring 2 ±0.2, and Tip +0.3/-0.2. The diagram is labeled P.382(16)\_FI.2.
+
+**Figure I.2 – Dimensions of the 3.5 mm diameter socket with five contact points and positioning of each contact spring**
+
+## Appendix II
+
+### **Audio connectivity for sockets with six contact points**
+
+(This appendix does not form an integral part of this Recommendation.)
+
+This appendix illustrates the optional dimensions of concentric plug and socket connectors with six contact points and is for further study.
+
+## Appendix III
+
+### **Audio connectivity for sockets with fewer than five contact points**
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Refer to Appendices I to III of [ITU-T P.381] for illustrations of dimensions of concentric plug and socket connectors with three and four contact points.
+
+## **Appendix IV**
+
+## **Other considerations**
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Refer to Appendix IV of [ITU-T P.381] for illustrations of other considerations when implementing a five pole plug and socket.
+
+# Bibliography
+
+- [b-ITU-T G.701] Recommendation ITU-T G.701 (1993), *Vocabulary of digital transmission and multiplexing, and pulse code modulation (PCM) terms.*
+- [b-ITU-T P.10] Recommendation ITU-T P.10/G.100 (2017), *Vocabulary for performance, quality of service and quality of experience.*
+- [b-ITU-T P.57] Recommendation ITU-T P.57 (2021), *Artificial ears.*
+- [b-ITU-T P.380] Recommendation ITU-T P.380 (2022), *Electro-acoustic measurements on headsets.*
+- [b-ITU-T P.800.1] Recommendation ITU-T P.800.1 (2016), *Mean opinion score (MOS) terminology.*
+- [b-ITU-T P.863] Recommendation ITU-T P.863 (2018), *Perceptual objective listening quality prediction.*
+- [b-IEC 60268-7] International Standard IEC 60268-7 (2010), *Sound system equipment – Part 7: Headphones and earphones.*
+
+
+
+
+
+# SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | Tariff and accounting principles and international telecommunication/ICT economic and policy issues                                                       |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| Series K        | Protection against interference                                                                                                                           |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| <b>Series P</b> | <b>Telephone transmission quality, telephone installations, local line networks</b>                                                                       |
+| Series Q        | Switching and signalling, and associated measurements and tests                                                                                           |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |