1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION= STANDARDIZATION SECTOR OF ITU P.502 (OW2 O0 O) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Objective measuring apparatus Objective test methods for speech communication systems using complex tes
2、t signals ITU-T Recommendation P.502 (Formerly CCITT Recommendation) ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Vocabulary and effects of transmission parameters on customer opinion of transmission Series P.10 quality Subscribers lines
3、 and sets Series P.30 Transmission standards Series P.40 P.300 Objective measuring apparatus Series P.50 II P.500 Objective electro-acoustical measurements Measurements related to speech loudness Methods for objective and subjective assessment of quality Audiovisual quality in multimedia services Se
4、ries P.60 Series P.70 Series P.80 P.800 Series P.900 For further details, please rer to the list of ITD-T Recommendations. ITU-T Recommendation P.502 Objective test methods for speech communication systems using complex test signals Summary This ITU-T Recommendation describes methods and procedures
5、for the evaluation of complex terminals, network components and transmission systems. The test methods mostly make use of test signals described in ITU-T Recommendations P.50, P.59 and P.501. For various technical implementations and conversational situations, the possible impacts on the speech qual
6、ity perceived subjectively are given and the relevant measurement procedures are described. Source ITU-T Recommendation P.502 was prepared by ITU-T Study Group 12 (1997-2000) and approved under the WTSC Resolution 1 procedure on 18 May 2000. Keywords Analysis methods, double talk, single talk, speec
7、h quality. ITU-T P.502 (05/2000) 1 FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (U-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, op
8、erating 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 tur
9、n, produce Recommendations on these topics. The approval of U-T Recommendations is covered by the procedure laid down in WTSC Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE I
10、n 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 inv
11、olve the use of a claimed Intellectual Property Right. U takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by U members or others outside of the Recommendation development process. As of the date of approval of this Recomme
12、ndation, 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. o m
13、u 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, without permission in writing from the ITU. 11 ITU-T P.502 (05/2000) CONTENTS Page 1 2 3 4 4.1 4.2 4.3 5 5.1 5.2 5.3 6 6.
14、1 6.2 6.3 7 7.1 7.2 7.3 8 8.1 8.2 8.3 Scope . References . Definitions and abbreviations . Convergence Performance of Echo Cancellers . Speech Quality Degradation Perceived Subjectively Related Objective Parameters for Single Talk Mode Analysis Methods 4.3.1 Convergence Time (T, ) Test Method 4.3.2
15、Echo return loss. temporally weighted (East) - single talk Speech Quality Evaluations during Double Talk Speech Quality Degradation Perceived Subjectively Related Objective Parameters . Analysis Methods 5.3.1 CSS double talk method 5.3.2 Double talk testing using parallel combined sequences Compandi
16、ng and AGC Characteristics . Speech Quality Degradation Perceived Subjectively Related objective Parameter . Analysis Methods Quality of Background Noise Transmission . Quality Degradation Perceived Subjectively Related objective Parameter . Analysis Methods Switching Characteristics Speech Quality
17、Degradation Perceived Subjectively Related Objective Parameters . Analysis Methods 8.3.1 Attenuation Range and Switching Characteristics 8.3.2 Threshold Level and Build-Up Time (for Minimum Activation Level) 8.3.3 Hangover time . (SND to RCV) . 8.3.4 8.3.5 Threshold Level and Switching Time to Switc
18、h Over from RCV to SND Switching Characteristics in the Presence of Background Noise 1 1 2 18 18 18 18 20 21 21 21 23 23 23 24 24 25 26 26 27 . ITU-T P.502 (05/2000) 111 Page Annex A . Detailed Test Methodology for Temporally Weighted E% A.l Echo Return Loss Algorithm A . 1.1 Echo Return Loss, Tempo
19、rally Weighted (ERb) A . 1.2 Modelling Echo Audibility A . 1.3 Expressing ERb Results . A.1.4 E% Test Algorithm . Annex B . Double talk measurement filters for Method A . Annex C . Training Sequence Description C . 1 Canceller Training prior to Double Talk C . 1.1 Double Talk Training Activity Masks
20、 . C . 1.2 Synchronizing the Double Talk Training Activity Masks . C . 1.3 Compensating for Measurement Filters . Appendix I . Bibliographic references Appendix II . Example Evaluations 11.1 Some Example Evaluations according to clause 5 . II.l.l Frequency Responses During Double Talk . II . 1.2 Lev
21、el Variations During Double Talk . II . 1.3 Switching During Double Talk 28 28 28 29 31 31 36 37 37 37 38 38 38 39 39 39 44 46 iv ITU-T P.502 (05/2000) Introduction This U-T Recommendation describes methods and procedures for the evaluation of complex terminals, network components and transmission s
22、ystems. Depending on the various parameters and systems to be measured, test methods are described. The test methods mostly make use of test signals described in ITU-T Recommendations P.50, P.59 and P.501. For various technical implementations and conversational situations, the possible impacts on t
23、he speech quality perceived subjectively are given and the relevant measurement procedures are described. ITU-T P.502 (05/2000) V ITU-T Recommendation P.502 Objective test methods for speech communication systems using complex test signals 1 Scope The aim of this U-T Recommendation is the definition
24、 of test methods which can be used to evaluate specific artifacts influencing the speech quality transmission of terminals and speech transmission systems. The methods described in this Recommendation are based on test signals as defined in U-T Recommendations P.50, P.59 and P.501. This Recommendati
25、on provides a collection of test methods which allow the investigation of various parameters which were found to be important for the assessment of speech communication systems. Each performance parameter is qualified by the speech degradation perceived subjectively and the related objective paramet
26、ers. For the individual parameters analysis methods are described. 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 val
27、id. 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 U-T Recommendatio
28、ns is regularly published. U-T Recommendation G. 122 (1 993), Influence of national systems on stability talker echo in international connections. U-T Recommendation G. 168 (2000), Digital network echo cancellers. U-T Recommendation P. 10 (1998), Vocabulary of terms on telephone transmission quality
29、 and telephone sets. U-T Recommendation P.50 (1999), Artzjkial voices. U-T Recommendation P.5 1 (1996), Artzjkial mouth. U-T Recommendation P.56 (1993), Objective measurement of active speech level. U-T Recommendation P.57 (1996), Artzjkial ears. U-T Recommendation P.58 (1996), Head and torso simula
30、tor for telephonometry. U-T Recommendation P.59 (1 993), Artzjkial conversational speech. U-T Recommendation P.340 (2000), Transmission characteristics of hands-free telephones. U-T Recommendation P.501 (2000), Test signals for use in telephonometry. U-T Recommendation P.581 (2000), Use of head and
31、torso simulator (HATS) for hands-free terminal testing. U-T Recommendation P.800 (1996), Methods for subjective determination of transmission quality. U-T Recommendation P. 8 1 O (1 996), Modulated noise reference unit (MNR U). ITU-T P.502 (05/2000) 1 - U-T Recommendation P. 830 (1 996), Subjective
32、performance assessment of telephone-band and wideband digital codecs. U-T Handbook on Telephonometry, 2nd edition; Geneva 1992. IEC 6065 1 (1 979), Sound Level Meters. - - 3 Definitions and abbreviations This ITU-T Recommendation defines the following terms: AGC characteristics: Characteristics of a
33、utomatic gain control systems. attenuation range (ad: Range in dB of attenuation inserted in sending or receiving direction of a terminal or system. Send Speech Attenuation During Double Talk (Asdt) Received Speech Attenuation During Double Talk (Ardt) attack time: Time needed to fully activate a tr
34、ansmission path (by a compander). crest factor: Peak-to-RMS ratio of a signal. companding: Level dependant attenuatiodamplification of a signal. Composite Source Signal (CSS): Signal composed in time by various signal elements. Echo Return Loss Enhancement (ERLE): Measure to determine the perceived
35、improvement of disturbance by echo signals. Echo Return Loss (ERL): Measure to determine the perceived disturbance by echo signals. Echo Return Loss, double talk (ERLdt): Measure to determine the perceived disturbance by echo signals in double talk conditions. Echo Return Loss, temporally weighted,
36、single talk (ERLbt): Measure to determine the perceived disturbance by echo signals in single talk conditions taking into account some psychoacoustic effects. Echo Return Loss, temporally weighted, double talk (ERLtdt): Measure to determine the perceived disturbance by echo signals in double talk co
37、nditions taking into account some psychoacoustic effects. Fast Fourier Transformation (FFT) Markov Speech Model Process (MSMP) See U-T Recommendation P.501. Non-Linear Processor (NLP): Processor used typically in echo cancellers to switch off the residual echo. Pseudo Noise sequence (PN-sequence) :
38、Pseudo-random noise with defined frequency-content, derived by inverse Fourier transformation of a predefined frequency spectrum. RCV: Receiving direction release time: Time needed to fully deactivate a transmission path (by a compander). Ri, (Receive input): (Electrical) receive access point of a d
39、evice under test. SND: Sending direction Saut (Send output): (Electrical) send access point of a device under test. 2 ITU-T P.502 (05/2000) TCL (Terminal Coupling Loss): Echo Loss of a terminal measured fi-om Ri, to S,t, including SLR and RLR. T, (Convergence Time) See 4.3.1. TH (hang-over time) See
40、 U-T Recommendation P.340. Tic (Initial Convergence Time) See convergence time. TR (build-up time) See U-T Recommendation P.340. T, (switching time) See U-T Recommendation P.340. VTH (threshold level) See U-T Recommendation P.340. 4 This clause describes the convergence performance of echo canceller
41、s. Methods for assessing the subjective effects of various parameters of echo cancellers are described and objective methods for describing these parameters are also suggested. Convergence Performance of Echo Cancellers 4.1 Depth of convergence, or echo return loss enhancement (ERLE) describes the a
42、bility of an echo canceller to cancel signals returned in the opposite transmission direction through an echo path. This can be acoustic echo in the case of a hands-free telephone, or hybrid echo in the case of a two to four-wire conversion. Poor ERLE means that residual echo signals will be more au
43、dible. Convergence time describes how fast the echo canceller reaches a stable state where returned residual echo signal is sufficiently attenuated without inserting loss in either speech transmission path. This is the time required to reach within 3 dB of ERL, and/or 25 dB loss. Fast convergence of
44、 an echo canceller is needed to prevent echo fi-om reaching a talker at the beginning of a call. Echo burst may be generated in a condition where an echo canceller may have trouble converging on a particular echo path. Subjective degradation is a function of the echo burst lengtldlevel, how close to
45、 each other they are, how many there are per minute, and the echo path delay. Speech Quality Degradation Perceived Subjectively 4.2 The quality of the echo control characteristics are determined by the following parameters: Related Objective Parameters for Single Talk Mode echo return loss as a func
46、tion of time, defined as Echo Return Loss (ERL); temporally weighted echo return loss (E%); time for AEC to converge, defined as Convergence Time (TJ. duplex performance as a function of time; response in duplex operation for the above parameters; In addition the following parameters apply in the do
47、uble talk situation: ITU-T P.502 (05/2000) 3 attenuation response in the presence of environmental or network impairments. The double talk parameters are dealt with in clause 5. 4.3 Analysis Methods The subclause below suggests some objective measurement techniques that can be used to assess the par
48、ameters described above. If network speech echo cancellers are tested, a proper test setup can be found in ITU-T Recommendation G.168. The test conditions for hands-free telephones can be found in ITU-T Recommendation P.340. 4.3.1 The description of the method to test convergence time of echo cancel
49、lers can be found in U-T Recommendation G.168. Therefore, the echo signal is measured using a level meter according to IEC 60651. An exponential weighting filter with a time constant of 35 ms (IEC 60651, “Impulse“) is applied when integrating the output of the level meter. The measured output signal is displayed as a level versus time diagram. Typically, a limit is given as a function of time which should not be exceeded. A typical example for such a diagram is shown in Figure 1. Convergence Time (TJ Test Method to ims 1 s+ +t
