1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Supplement 3 TELECOMMUNICATION (Series P) STANDARDIZATION SECTOR OF ITU (03/93) TELEPHONE TRANSMISSION QUALITY MODELS FOR PREDICTING TRANSMISSION QUALITY FROM OBJECTIVE MEASUREMENTS Supplement 3 to ITU-T Series P Recommendations (Previously CCITT Recommen
2、dations) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom-munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunic
3、ations on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. Supplement 3 to ITU-T Series P Recommendations was revis
4、ed by the ITU-T Study Group XII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). _ NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Stan
5、dardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms
6、 CCITT, CCIR or IFRB or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 In this Recommendation, the expression Administration is used for conciseness to indicate both
7、a telecommunication administration and a recognized operating agency. ITU 1994 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. Suppl
8、ement 3 Series P (03/93) i CONTENTS Supplement 3 Series P (03/93) Page 1 Transmission rating models 1 1.1 Introduction 1 1.2 Transmission rating models 2 1.3 Subjective opinion models 13 2 Prediction of transmission qualities from objective measurements . 16 2.1 Types of model . 16 2.2 Model and pro
9、grams: SUBMOD, CATPASS and CATNAP. 16 2.3 Situation to be represented 17 2.4 Outline of the model . 17 2.5 Calculation of loudness and loudness ratings . 18 2.6 Calculation of listening effort score 18 2.7 Calculation of Conversation Opinion Score . 22 2.8 Evaluation of other subjective measures of
10、performance . 22 2.9 Correspondence between calculated and observed values 24 2.10 Incorporating miscellaneous degradations 25 2.11 Practical use of the model. 26 3 Calculation of transmission performance from objective measurements by the information index method 27 3.1 Introduction Type of model .
11、 27 3.2 Application to digital transmission . 27 3.3 Application to analogue transmission. 29 3.4 Possible extensions . 36 4 Overall Performance Index model for Network Evaluation (OPINE) . 36 4.1 Introduction 36 4.2 Outline of the model . 37 4.3 Configuration of OPINE. 39 4.4 Symbol types and value
12、s. 46 Annex A (reference to 1.1) Opinion ratings of transmission impairments. 56 A.1 Introduction 56 A.2 Overall loudness rating and circuit noise 57 A.3 Quantization noise from PCM processes 57 A.4 Bandwidth. 57 A.5 Listener echo. 57 A.6 Talker echo . 57 A.7 Sidetone 57 Annex B (reference to 2.9) C
13、alculated transmission performance of telephone networks 68 B.1 Introduction 68 B.2 HRC 1 Own exchange call . 69 B.3 HRC 2 Limiting national call 69 B.4 HRC 3 Long distance call with a PCM junction. 69 B.5 HRC 4 Asymmetry of transmission loss. 69 B.6 HRC 5 Effect of room noise . 69 B.7 HRC 6 Effect
14、of circuit noise and bandlimiting . 69 B.8 HRC 7 Multiple calculations with random selection of items 70 B.9 HRC 8 Example of the use of CATNAP to meet a design criterion. 70 B.10 HRC 9 Effect of varying line length. 70 ii Supplement 3 Series P (03/93) Page Annex C (reference to 4.3.1.2) Noise spect
15、rum calculation. 80 Annex D (reference to 4.3.3) MOS calculation examples 81 Annex E ( reference to 4.3.2.2) Derivation of equation (4-16) 84 Annex F (reference to 4.3.3) Psychological evaluation model. 85 F.1 Psychological model for evaluation 85 F.2 Derivation of equation (4-35) from equation (4-3
16、4). 86 Annex G Objective method of estimating the qualityof speech degraded by non-linear distortion. 87 G.1 Introduction 87 G.2 Scope 87 G.3 Measurement signal 87 G.4 Preprocessing 88 G.5 Objective parameters 89 G.6 Estimation process 92 Appendix I (reference to 3.2.2) Computer programs used . 97 I
17、.1 Computer program 1. 97 I.2 Computer program 2. 97 Appendix II (reference to 3.2.2 and 3.3) . 99 Appendix III (reference to 3.3.2) Calculation of the DATA in Appendix II from primary data 101 III.1 Definition of the primary data 101 III.2 Relations . 102 III.3 Example 102 References . 103 Suppleme
18、nt 3 Series P (03/93) iii INTRODUCTION Models for predicting the subjective opinion of telephone connections, using data from objective measurements, are currently under study. It has not been possible up to now to recommend a single model applicable over a wide range of transmission impairments, bu
19、t the methods described in clauses 1, 2, 3 and 4 below have been proposed by several Administrations. Supplement 3 - Series P (03/93) 1 Supplement 3 - Series P Supplement 3 - Series P (03/93) MODELS FOR PREDICTING TRANSMISSION QUALITY FROM OBJECTIVE MEASUREMENTS (referred to in Series P Recommendati
20、ons) 1 Transmission rating models (Geneva, 1980; modified at Malaga-Torremolinos, 1984) (Quoted in clause 3/P.11) (Contribution by the United States of America and Canada) 1.1 Introduction This clause describes transmission rating models which can be used to estimate the subjective reaction of telep
21、hone customers to the transmission impairments of circuit noise, overall loudness rating, talker echo, listener echo, attenuation distortion (including bandwidth), quantizing distortion, room noise and sidetone. The models for circuit noise overall loudness rating (OLR) and talker echo are based on
22、several conversational tests conducted at Bell Laboratories in the period from 1965 to 1972 to evaluate the subjective assessment of transmission quality as a function of circuit noise, overall loudness rating, talker echo path loss and talker echo path delay 1. These tests involved several hundred
23、subjects and several thousand test calls. Several tests were conducted on normal business calls. Others were conducted in the laboratory. All of the tests employed a five-category rating scale: excellent, good, fair, poor and unsatisfactory. The essential features of the models were originally deriv
24、ed in terms of loudness loss of an overall connection in dB (as measured by the Electro-Acoustic Rating System, EARS) and circuit noise in dBmp at the input to a reference receiving system (electric-to-acoustic efficiency as measured by the EARS) 2. The effects of talker echo were later incorporated
25、 in terms of loudness loss of the echo path in dB (as measured by the EARS) and round trip delay of the echo path in milliseconds. Experimentally determined correction factors were used to convert the models to loudness ratings according to Recommendation P.79. The original model for listener echo w
26、as based on a series of four listening-type subjective tests conducted at Bell Laboratories in 1977 and 1978 3. Subsequent test results led to an alternative form of the model. The subjective tests included conditions in which the listener echo path loss was flat or frequency-shaped by selective fil
27、tering. A weighted echo path loss is defined to provide a weighting of the frequency-shaped test conditions so that subjectively equivalent test conditions have the same transmission rating. The model for quantizing distortion is based on a series of five subjective tests conducted to evaluate the p
28、erformance of various digital codec algorithms 6, 7, 8. The model for bandwidth and attenuation distortion is based on tests conducted in 1978 9. The model for room noise is based on unpublished tests conducted in 1976. Opinion ratings of transmission quality on a five-category scale were made by 40
29、 subjects for 156 conditions having various combinations of room noise, speech level, circuit noise and sidetone path loss. The samples of room noise were presented from tape recordings made in an airlines reservations office. A model was fitted to the test results in terms of the circuit noise whic
30、h produced the same quality ratings as given levels of room noise. The model for sidetone is based on tests conducted in 1980 10. All of the tests were conducted with Western Electric 500-type telephone sets or equivalent. The procedures used in the analysis of the subjective tests results and the d
31、erivation of the transmission rating scale are outlined in 1. Although the procedures are somewhat complex for manual calculation, they are easily handled on a digital computer and have been found to provide a convenient and useful representation for a large variety of test data. 2 Supplement 3 - Se
32、ries P (03/93) The models incorporate the concept of a transmission rating scale. An important reason for the introduction of this scale was the recognition that subjective test results can be affected by various factors such as the subject group, the type of test, and the range of conditions which
33、are included in the test. These factors have been found to cause changes in both the mean opinion score of a given condition and in the standard deviation. Thus, there are difficulties in trying to establish a unique relationship between a given transmission condition and subjective opinion in terms
34、 of mean opinion score or percent of ratings which are good or excellent. The introduction of a transmission rating scale tends to reduce this difficulty by separating the relationship between transmission characteristics and opinion ratings into two parts. The first part, the transmission rating as
35、 a function of the transmission characteristic, is anchored at two points and tends to be much less dependent on individual tests. The second part, the relationship between the transmission rating and subjective opinion ratings, can then be displayed for each individual test. The transmission rating
36、 scale for overall loudness rating and circuit noise was derived such that it is anchored at two points as shown in Table 1-1. TABLE 1-1 These anchor points were selected to be well separated but within the range of conditions which are likely to be included in a test. The rating values are such tha
37、t most connections will have positive ratings between 40 and 100. Transmission ratings for other combinations of loudness rating and circuit noise are relative to those for these two anchor points. This clause presents the transmission rating models in terms of overall loudness rating of an overall
38、connection in dB, circuit noise in dBmp referred to the input of a receiving system with a receiving loudness rating (RLR) = 0 dB, loudness rating of the talker echo path in dB, and round-trip delay of the talker echo path in milliseconds. Annex A illustrates representative opinion results. 1.2 Tran
39、smission rating models 1.2.1 Overall loudness rating and circuit noise The transmission rating model for overall loudness rating and circuit noise is RLN= 26.76 2.257 (Le 8.2)2+ 1 2.0294 NF+ 1.751 Le+ 0.02037 Le NF(1-1) where Leis the OLR of an overall telephone connection (in dB). NOTE In equation
40、(1-1) the value of Lecan be replaced by Le +Lsto provide a loudness loss correction in (Ls) in dB. This compensates for reduced talker speech level when the sidetone masking rating (STMR) at the talker end of the connection is less than 15 dB. The correction Lsis zero when STMR = 12, the default val
41、ue. Otherwise, the correction Lsis given as follows: Ls= 0.3 (STMR 12) if STMR 3200 Hz, a value of 3200 Hz should be used.) Sl, Suis the lower and upper inband response slopes (in dB/octave) below and above 1000 Hz, respectively, which would have the same loudness loss as the actual response shapes.
42、 Figures 1-3 and 1-4 illustrate the effect of the band limits, Fland Fu, and inband slopes, Sland Su, on the bandwidth factor, kBW. Figure 1-4 makes use of the expression for k3k4in Note 2 below. NOTES 1 The functions for the bandwidth factor, kBW, have been selected such that kBW= 1 when Fl= 310 Hz
43、, Fu= 3200 Hz, Sl= 2 dB/octave and Su= 3 dB/octave. These response characteristics are representative of those used in the tests to formulate the transmission rating model for overall loudness rating and circuit noise. 2 In accordance with test results conducted in 1987 and with little change in the
44、 predicted results the product k3k4can be replaced with k3k4= 0.93 + 0.0627 (Sl+ 0.441 Su) 0.00012 (Sl+ 0.441 Su+ 7.17)3Supplement 3 - Series P (03/93) 7 200 250 300 350 400 450 500 HzT1204060-92/d0332003000280026001.21.11.00.80.70.6FIGURE 1-3Bandwidth model factorHigh-frequency cutoff, Fu (Hz)u0.9B
45、andwidthfactor(k1k2)12Low-frequency cutoff (Fl)lFIGURE 1-3.D03 = 12.8 CM 8 Supplement 3 - Series P (03/93) T1203730-91/d042101234562261.11.051.00.950.90.850.80.750.7FIGURE 1-4Attenuation Distortion model factorHigh-frequency slope,Su (dB/octave)uLow-frequency slope, Sl (dB/octave)lSlope factor(k3k4)
46、34FIGURE 1-4.D04 = 12 CM 1.2.5 Listener echo The transmission rating model for listener echo is RLE= 9.3 (WEPL + 7) (DL 0.4)0.229 (1-20) where WEPL is the Weighted Listener Echo Path Loss (in dB) and WEPL = 20 log1013200200340010 EPL ( f )20df (1-21) EPL( f ) is the echo path loss (in dB) as a funct
47、ion of frequency in Hz. DLis the round-trip listener echo path delay in milliseconds. Supplement 3 - Series P (03/93) 9 Transmission rating, RLE, as a function of the weighted echo path loss and listener echo-path delay is shown in Figure 1-5. 100908070605040024681012dBT1204070-92/d05112481632Echo-p
48、ath delay (ms)Weighted echo-path lossOriginal modelAlternate modelFIGURE 1-5Transmission rating for listener echoTransmissionrating(RLE)LEFIGURE 1-5.D05 = 14.5 CM The transmission rating for listener echo, RLE, can be combined with the transmission rating for overall loudness rating and circuit nois
49、e to give an overall transmission rating as follows: RLNLE= RLN+ RLE2 RLN RLE22+ 132(1-22) Figure 1-6 provides curves generated by means of the above relationship for transmission rating as a function of weighted listener echo path loss and listener echo path delay in a connection with an overall loudness rating of 16 dB and a circuit noise of 56 dBmp referred to a RLR of 0 dB. 10 Supplement 3 - Series P (03/93) 80706050
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