1、COVERING NOTE GENERAL SECRETARIAT INTERNATIONAL TELECOMMUNICATION UNION Geneva, 31 March 2004 ITU - TELECOMMUNICATION STANDARDIZATION SECTOR Subject: Corrigendum 1 (03/2004) to ITU-T Recommendation P.340 (05/2000), Transmission characteristics and speech quality parameters of hands-free terminals As
2、 the subject of Clause 10 “Acoustic echo controllers and speech enhancement devices“ of ITU-T Rec. P.340 is now integrated in ITU-T Rec. P.330, Clause 10 is deleted fi-om ITU-T Rec. P.340. Union internationale des tlcommunications Place des Nations 121 1 GENVE 20 Suisse - Switzerland - Suiza INTERNA
3、TIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STAN DARD IZATION SECTOR OF ITU P.340 (OW2 O O O) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Subscribers lines and sets Transmission characteristics and speech quality parameters of hands-free terminal
4、s ITU-T Recommendation P.340 (Formerly CCITT Recommendation) ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS II - Vocabulary and effects of transmission parameters on customer opinion of transmission quality Series P.10 - Transmission stand
5、ards Series P.40 Objective measuring apparatus Objective electro-acoustical measurements Measurements related to speech loudness Methods for objective and subjective assessment of quality Audiovisual quality in multimedia services Series P.50 Series P.60 Series P.70 Series P.80 P.800 Series P.900 P.
6、500 For further details, please refer IO the list of iTU- T Reconimendations. ITU-T Recommendation P.340 Transmission characteristics and speech quality parameters of hands-free terminals Summary This Recommendation defines the generic transmission characteristics of hands-free terminals, whatever t
7、he applications or technologies integrated. In addition to the parameters that ensure performance levels equivalent to these of handset terminals (sensitivity values, response curves, etc.), it defines the parameters which have a bearing on conversation quality (gain switching characteristics, doubl
8、e-talk performances,etc.). It also defines categories of hands-free terminals based on the terminals double-talk capability. This Recommendation deals with the characteristics of the signal-processing equipment (e.g. acoustic echo cancellation (AEC) that can be incorporated in hands-free terminals.
9、Source ITU-T Recommendation P.340 was revised by ITU-T Study Group 12 (1997-2000) and approved under the WTSC Resolution 1 procedure on 18 May 2000. FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommu
10、nication 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 Confe
11、rence (WTSC), 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 WTSC Resolution 1. In some areas of information technology wh
12、ich fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 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 PRO
13、PERTY 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 asser
14、ted 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 t
15、hat this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o ITU 2001 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
16、, without permission in writing from ITU. CONTENTS Introduction Page 1 1 2 3 4 4.1 4.2 4.3 4.4 4.5 4.6 5 5.1 5.2 5.3 5.4 5.5 5.6 6 7 7.1 7.2 7.3 7.4 I 7.5 7.6 7.7 Normative references Definitions and abbreviations . Transmission charactenstics . Sending sensitivity Receiving sensitivity . . . Freque
17、ncy response curves . 4.3.1 Sending 4.3.2 Receiving . Subjective evaluations of loudness ratings . 4.4.2 Receiving . Objective evaluations of sensitivity and loudness ratings 4.5.1 Sensitivity measurement . Switching parameters . Testing conditions Test arrangement Calibration of the artificial mout
18、h Test environment 4.4.1 Sending 4.5.2 Measure and computation of loudness ratings Test table Test signals . Conversational quality Test signal levels Parameters measured instrumentally Attenuation range aH Attenuation distribution at idle mode . Hang-over time . Dynamic compression Reverberance Tim
19、e-dependent transfer function Duplex behaviour . Speech detection . Control characteristics of echo cancellation . 1 2 4 4 4 4 4 5 5 5 5 6 6 7 7 9 9 9 10 11 13 13 13 14 14 14 15 15 15 16 16 17 17 . 7.10 7.11 8 8.1 8.2 9 10 10.1 10.2 10.3 Speech detection with ambient noise . Background noise transmi
20、ssion Behaviour of hands-flee terminals in double talk situation Categonzation . Terminal coupling loss in double talk situation . Parameters to be evaluated for each type of HFT Acoustic echo controllers and speech enhancement devices Functional units Delay . 10.2.1 Processing delay 10.2.2 Round tr
21、ip echo path delay (EPDn) - network interface Acoustic echo control specifications 10.3.1 Acoustic echo path 10.3.2 Parameters and recommended limits . Annex A . Test results A.l Categorization of hands-fiee terminals based on double talk performance . A . 1.1 A.1.2 A.1.3 Relationship between Listen
22、ing only tests, Double talk tests and Conversation Results of the listening only tests with variable attenuations in sending Results of the listening only tests with variable attenuations in receiving path path Results of listening only tests on echo disturbance . tests: comparison of six different
23、hands-free terminals Appendix I - Preliminary values . 1.1 Double talk performance 1.2 Build-up time characteristics Appendix II - Examples of processing delays for mobile hands-flee terminal . Taddqroc (additional time for processing) . A.2 1.3 Level adjustments by companding or AGC . 11.1 Example
24、1 . 11.2 Example 2 . Appendix III - Recommended test bed . III . 1 111.2 Example 1 : Implemented test hybrid Example 2: Adaptive Echo Canceller . Appendix IV - Bibliography . Page 17 18 19 19 19 20 21 21 22 22 22 22 23 23 25 25 25 26 27 29 33 33 34 34 35 35 35 35 36 36 36 38 Introduction The object
25、of this Recommendation is to obtain for hands-free terminals transmission performance equivalent with handset telephones, at least with respect to send and receive loudness. Other important features contributing to the quality of telephone calls made from hands-free terminals, as switching character
26、istics, duplex capability, are defined in this Recommendation. This Recommendation covers generic characteristics and requirements that are applicable to both analogue and digital hands-fiee terminals. Additional requirements that are applicable strictly to digital terminals can be found in ITU-T P.
27、342 3 and P.341 4. For loudspeaking telephones (see ITU-T P.10 14) which do not provide full hands-free operation, the relevant parts of this Recommendation may be referred to. Test methods appropriate for parameters defined in this Recommendation may be found in ITU-T P.502 12. For the use of HATS
28、for testing, ITU-T P.581 21 applies. ITU-T Recommendation P.340 Transmission characteristics and speech quality parameters of hands-free terminals 1 Introduction The object of this Recommendation is to obtain for hands-free terminals transmission performance equivalent with handset telephones, at le
29、ast with respect to send and receive loudness. Other important features contributing to the quality of telephone calls made fi-om hands-free terminals, as switching characteristics, duplex capability, are defined in this Recommendation. This Recommendation covers generic characteristics and requirem
30、ents that are applicable to both analogue and digital hands-free terminals. Additional requirements that are applicable strictly to digital terminals can be found in ITU-T P.342 3 and P.341 4. For loudspeaking telephones (see ITU-T P.10 14) which do not provide full hands-fi-ee operation, the releva
31、nt parts of this Recommendation may be referred to. Test methods appropriate for parameters defined in this Recommendation may be found in ITU-T P.502 12. For the use of HATS for testing, ITU-T P.581 21 applies. 2 Normative references The following ITU-T Recommendations and other references contain
32、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 th
33、e 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. i 2 3 141 5 ITU-T G. 12 1 (1 993), Loudness Ratings (LRs) of national systems. CCITT G.223 (1 988), Assumptions for
34、the calculation of noise on hypothetical reference circuits for telephony. ITU-T P.342 (2000), Transmission characteristics for telephone band (300-3400 Hz) digital loudspeaking and hands-free telephony terminals. ITU-T P.341 (1998), Transmission characteristics for wideband (150-7000 Hz) digital ha
35、nds-free telephony terminals. ITU-T P.78 (1996), Subjective testing method for determination of loudness ratings in accordance with Recommendation P. 76. 6 7 SI 9 1 O 111 121 ITU-T P.79 (1 999), Calculation of loudness ratings for telephone sets. ITU-T P.50 (1999), Artificial voices. ITU-T P.51 (199
36、6), ArtiJicial mouth. ITU-T P.501 (2000), Test signals for use in telephonometiy. ITU-T G. 167 (1 993), Acoustic echo controllers. ITU-T Handbook on Telephonometry, 1993. ITU-T P.502 (2000), Objective test methods for speech communication systems using complex test sigrzals. ITU-T P.832 (2000), Subj
37、ective performance evaluation of handsfree terminals. ITU-T P. 1 O (1 998), Vocabulary of terms on telephone transmission quality and telephone sets. ITU-T G. 1 14 (2000), One-way transmission time. ITU-T G. 13 1 (1 996), Control of talker echo. ITU-T G. 174 (1 994), Transmission performance objecti
38、ves for terrestrial digital wireless systems using portable terminals to access the PSTN. ITU-T G.122 (1993), InJluence of national systems on stability and talker echo in international connections. ITU-T P.800 (1 996), Methods for subjective determination of transmission quality. ITU-T G. 168 (2000
39、), Digital network echo cancellers. ITU-T P.581 (2000), Use of head and torso simulator (HATS) for hands-free terminal testing. 3 Definitions and abbreviations The relevant definitions given in ITU-T P. 10 apply along with the following: 3.1 hands-free reference point (HFRP): A point located on the
40、axis of the artificial mouth, at 50 cm from the lip ring, where the level calibration is made, in free field. It corresponds to the measurement point 1 1, as defined in ITU-T P.5 1 81. 3.2 hands-free (telephone) set (HFT): A telephone set using a loudspeaker associated with an amplifier as a telepho
41、ne receiver and which may be used without a handset. 3.3 loudspeaking (telephone) set (LST): A handset telephone using a loudspeaker associated with an amplifier as a telephone receiver. 3.4 acoustic echo canceller (AEC): A device which reduces the acoustic echo level with negligible effects on the
42、local and distant users speech. It is generally implemented by adaptive identification of the acoustic echo path response. 3.5 loss controller: A device which reduces the acoustic echo level by inserting variable losses on the received andor transmitted audio signals. 3.6 non-linear processor: A dev
43、ice which reduces or cancels small echo signals by non-linear operation on the samples of the transmitted audio signal. A centre-clipper is a typical device of this kind. 3.7 supplementary howling control device: A device which modifies some characteristics of the transmitted and/or received signals
44、 in order to improve the stability margin of the terminal. This function is typically implemented by a harmonic processor. To prevent network disturbances, such devices should be avoided in the case of terminals likely to be used on connections including network electric echo cancellers conforming t
45、o ITU-T G.168 20 which are not able to work properly with time-variant echo paths (e.g. frequency shift). 3.8 noise reduction system: A device which increases the signal-to-noise ratio (on the overall or a specific range of bandwidth of the signal). This Recommendation uses the following abbreviatio
46、ns: AEC Acoustic echo canceller AGC Automatic gain control aH Insertion attenuation range (dB) aH,S H,R Ardt Asdt css Drdt Dsdt EEB EPDn ERL ERLtst ERLtdt HFT HFRP LOT MRP MOS OLR UR SLR TCLwdt TCLwst TCLtst TCLtdt Tc Tic TR TRdt TRst TS TUT VTH Attenuation range (dB) in the sending path Attenuation
47、 range (dB) in the receiving path Received speech attenuation (dB) during double talk Sent speech attenuation (dB) during double talk Composite Source Signal (see ITU-T P.5019) Received speech distortion during double talk Sent speech distortion during double talk Early Energy Balance Round trip ech
48、o path delay - network interface Echo return loss Temporally weighted echo return loss - single talk Temporally weighted echo return loss - double talk hands-f?ee terminal Hands-Free Reference Point Listening Only Test (see ITU-T P.832 131) Mouth Reference Point Mean Opinion Score (see ITU-T P.800 1
49、9) Overall Loudness Rating Receiving Loudness Rating Sending Loudness Rating Weighted terminal coupling loss - double talk Weighted terminal coupling loss - single talk Terminal Coupling Loss temporally weighted - single talk Terminal Coupling Loss temporally weighted - double talk Convergence time Initial convergence time Build-up Time Build-up time - double talk Build-up time - single talk Hang-over Time Switching Time Terminal Under Test Threshold Level 4 Transmission characteristics 4.1 Sending sensitivity The Sending LR (SL
