1、ETSI ETR+250 cfib 3400855 01 t TSI .c 1 ECHNICAL R EPORT ETR 250 July 1996 Source: ETSI TC-TM Reference: DTFUTM-05006 ICs: 33.040.20 Key words: transmission, network, 3,l kHz, speech, quality, planning, methodology Transmission and Multiplexing (TM); Speech communication quality from mouth to ear fo
2、r 3,l kHz handset telephony across networks ETSI European Telecommunications Standards Institute ETSI Secretariat Postal address: F-O6921 Sophia Antipolis CEDEX - FRANCE Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE X.400: c=fr, a=atlas, p=etsi, s=secretariat - Intern
3、et: secretariat Qetsi.fr Tel.: +33 92 94 42 O0 - Fax: +33 93 65 47 16 Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. O European Telecommunications Standards Institute 1996.
4、 All rights reserved. ETSI ETRr250 96 W 3400855 0130958 VT7 W Page 2 ETR 250: July 1996 Whilst every care has been taken in the preparation and publication of this document, errors in content, typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to “ETSI
5、Editing and Committee Suoort Deot.“ at the address shown on the title Daae. ETSI ETRx250 96 3400855 0130959 333 6.1 6.2 6.3 6.4 6.5 Page 3 ETR 250: July 1996 Contents Foreword . 11 Introduction 11 1 Scope 13 2 References 13 3 Definitions and abbreviations 21 3.1 Definitions 21 3.2 Abbreviations . 22
6、 Typical network components and configurations 24 4.1 Network components . 24 4.2 Network configurations 24 General considerations; individual parameters and combination effects 26 Individual transmission parameters . 28 4 5 6 I General survey of the individual transmission parameters 28 6.1.1 Overv
7、iew 28 6.1.2 The human speech and hearing parameters 28 6.1.3 The voice transmission attenuation between talker and listener . 33 6.1.4 Talker and listener sidetone 33 6.1.5 Echo and stability 33 6.1.6 Transmission time . 34 6.1.7 Noise and quantizing distortion . 34 6.1.8 Power handling and non-lin
8、ear distortion 34 6.1.9 Crosstalk . 34 Basic attenuatiodfrequency response parameters . 34 General 34 6.2.1 6.2.2 Handset telephone characteristics 36 6.2.3 Subscriber line attenuation 40 6.2.4 4-wire circuits 41 Overall, send, receive and circuit loudness ratings . 43 6.3.1 General 43 6.3.2 Overall
9、 Loudness Rating (OLR) 44 6.3.3 Send and Receive Loudness Ratings (SLR and RLR) 44 6.3.4 Conversions to and from other loudness loss related values 44 Sidetone . 45 6.4.1 General 45 6.4.2 Electric and acoustic paths of the sidetone, calculation of STMR and LSTR . 45 6.4.3 Relation between STMR and L
10、STR 47 6.4.4 Recommendations for STMR 47 6.4.5 Recommendations for LSTR . 49 6.4.6 Sidetone distortion . 49 6.4.7 A comparison between talker sidetone and talker echo 50 Echo and stability . 50 6.5.1 General 50 6.5.2 The principle of echo . 50 6.5.2.1 Talker echo 50 6.5.2.2 Listener echo . 51 6.5.2.
11、3 Echo sources and echo loss 51 6.5.2.4 Multiple echoes 53 6.5.3 Stability 53 6.5.4 Definitions for echo and stability 54 - . ETSI ETR*250 96 3YOOB55 OL30b0 O55 Page 4 ETR 250: July 1996 6.5.5 Methods for the control of echo and stability 56 6.5.5.1 Loss contribution . 56 6.5.5.2 Echo control device
12、s . 57 Acceptable limits and planning rules 57 6.5.6.1 Limits for stability . 57 6.5.6.2 Limits for echo . 58 6.6 Transmission time . 62 6.6.1 Limits for transmission time 62 6.7 Noise and quantizing distortion . 63 6.7.1 General . 63 6.7.2 Circuit noise, quantizing noise and distortion 64 6.7.3 Add
13、ition of noise sources in a connection; equivalent noise in a O dBr point 65 6.7.4 Ambient (room) noise . 65 6.7.5 Induced noise on subscriber lines 66 6.7.6 The subjective effects of non-stationary noise . 66 Power handling and non-linear distortion 67 6.8.1 Amplitude characteristics of the speech
14、signal . 67 6.8.2 Power handling, FDM systems . 68 6.8.3 Power handling, PCM systems . 69 6.8.4 Measurements of actual signal levels in networks . 69 6.8.5 Effects of non-linear distortion 70 6.9 Crosstalk . 70 6.9.1 General . 70 6.9.2 Subjective effects of crosstalk characterized by Crosstalk Recei
15、ve Loudness Rating (XRLR) 71 Effects of time-varying impairments 72 6.5.6 6.8 6.1 O 7 Equipment and systems with special transmission properties . 72 7.1 Echo control devices . 72 7.1 . 1 Echo suppressors . 73 7.1.2 Echo cancellers 73 7.1.3 Planning rules for ECDs . 74 Low bit-rate codecs . 74 7.2.1
16、 Introduction . 74 7.2.2 ITU-T PCM, ADPCM and LRE (Low Rate Encoding) algorithms . 75 7.2.3 ETSI speech coding algorithms 76 7.2.4 Other regional speech coder algorithms . 77 7.2.5 General: New low bit-rate codecs and their properties . 77 7.2.6 7.2.7 Objective and subjective speech evaluation measu
17、res 81 7.2.8 Conclusion 81 Digital Circuit Multiplication Equipment (DCME) . 82 7.3.1 General . 82 7.3.2 Some data for a G.763 type DCME 83 Mobile communication systems 83 7.4.1 General . 83 7.4.2 Delay and echo . 84 7.4.3 Stability loss 85 7.4.4 Quantization distoition 85 7.4.5 Clipping (temporal)
18、. 85 7.4.6 Noise contrast and comfort noise . 85 7.4.7 Random bit errors and bursts of errors . 85 7.4.8 Speech coder performance 85 7.4.9 Examples of mobile communication systems . 85 7.5 ATM systems 86 7.5.1 General . 86 7.5.2 Delay . 87 7.2 Effect of coder parameters on the quality . 79 7.3 7.4 8
19、 Combination effects of impairments on speech communication quality . background to the ETSI model 88 8.1 Introduction 88 8.2 Derivation of the ETSI model 88 - ETSI ETR*250 b = 3400855 OL3ObL TL = Page 5 ETR 250: July 1996 8.3 8.4 8.5 Estimates of users reactions given in the ETSI model 90 Discussio
20、n of ratings and impairment factors in the ETSI model 91 Future up-dating and amendments of the ETSI model 93 9 A computation model for the overall voice transmission quality from mouth to ear 93 9.1 Description of algorithms in the ETSI model 93 9.1.1 Introduction 93 9.1.2 “Quality measures“ provid
21、ed by the ETSI model . 93 9.1.3 The transmission rating factor R . 96 9.1.3.1 General 96 9.1.3.2 Noise considerations and the basic “signal-to-noise“ factor Ro 96 9.1.3.3 9.1.3.4 The “delayed impairment“ factor id . 101 9.1.3.5 The “equipment impairment“ factor le . 105 9.1.3.6 The “expectation“ fac
22、tor A . 106 Comparisons of results from the ETSI model, other models and subjective tests 106 9.2.1 Introduction 106 9.2.2 Translation of R-values into GOB, POW, TME, MOS . 107 9.2.3 Overall loudness rating OLR and circuit noise Nc . 109 9.2.4 The influence of ambient noise via the listener sidetone
23、 112 9.2.5 Echoes 113 9.2.6 Quantizing distortion unit, qdu . 116 9.2.7 Impairments caused by low bit-rate codecs 117 9.2.8 The influence of long delays 118 9.2.9 Conclusions . 119 Future verification of the ETSI model 120 Application of the ETSI model in transmission planning 120 9.4.1 General 120
24、9.4.2 Interpreting subjective test results and predictions; some precautions to be observed . 121 9.4.3 9.4.4 Recommended limits for the R-factor etc . to be used in transmission planning of networks . 122 Statistical use of the ETSI-model for quality control of existing networks: some guidelines .
25、122 9.5.1 General 122 9.5.2 The statistical approach 123 The “simuitaneous-impairment“ factor Is . 99 9.2 9.3 9.4 Steps in the application of the ETSI computation model . 121 9.5 10 Assessment of end-to-end voice transmission performance of networks . 125 10.2 . Assessment of customer opinion . 125
26、1 0.1 General 125 10.3 Objective parameter measurements . 126 10.3.1 General 126 10.3.2 In-service non-intrusive measurement 126 10.3.2.1 Application . 127 10.3.2.2 Measurements . 128 10.3.2.3 Testing . 128 10.3.2.4 Modelling . 128 10.3.3 Speech Transmission Index (STI) . 129 Annex A: Impedance stra
27、tegy in 2-wire networks 130 A.l Introduction 130 A.2 Calculation of TELR. STMR and LSTR . 131 A.3 Formulas for unloaded cables . 132 A.4 Examples of cables terminated by different impedances; a compromise nominal impedance 133 AS Conclusions regarding choice of nominal impedances . 136 Page 6 ETR 25
28、0: July 1996 ETSI ETRm250 b m 3400855 OL309b2 928 m A.6 A note on the difference “etween the actual and the nominal input impedance of a digital exchange 137 A.7 Sidetone. impedance matching and line loss . 138 Annex B: Noise aspects in understanding overall network performance . 140 B.l Introductio
29、n . 140 8.2 Noise uncorrelated with the signal 140 8.3 Signal correlated noise . 140 8.4 Remarks regarding certain noise parameters 141 8.4.1 impulsive noise 141 8.4.2 Bursts of errored bits. loss of cells in ATM. etc . 141 Annex C: Absolute and relative level 142 C.1 General . 142 C.2 The unit “dB“
30、 . 142 C.3 The unit “dBm“ 142 C.4 The unit “dBr“ . 143 C.5 The unit “dBm0 145 C.6 The letter “p“ in “dBrnp“ and “dBmOp“ 145 C.7 The relationship between dBm. dBr and dBmO 146 C.8 Correction factors . 146 Annex D: Technical report on echo cancelling . 149 D.l Scope. purpose and application . 149 D.2
31、Historical background . 149 D.2.1 PSTN transmission planning . 149 D.2.2 Echo suppressors . 149 D.2.3 Echo cancellers . 151 D.2.4 Responsibilities of modem manufacturers and end users 152 D.3 Reference connection . 152 D.3.2 Terminology . 153 D.3.1 Echo control reference model . 152 D.4 Application
32、rules and operational constrains 154 D.4.1 Public network transmission planning . 154 D.4.1 . 1 Transmission levels 154 D.4.2 Delay considerations . 154 0.4.2.1 Echo return loss 154 D.4.3 Provisioning or the tail length 154 0.4.4 End user/manufacturer/ptivate network transmission planning 155 D.4.4.
33、1 Transmission levels 155 D.4.4.2 Delay considerations . 155 0.4.4.3 Echo return loss 155 D.5 Effect of cancellers on voice and data services 155 D.5.1 Interaction with voiceband data . 155 ETSI ETRx250 96 3400855 0330963 864 = Page 7 ETR 250: July 1996 D.5.2 Interaction of echo control with facsimi
34、le transmission 155 D.6 High-level speech 157 D.6.1 Introduction 157 0.6.2 Double-talk detection . 157 D.6.3 Effects of a non-linear echo path . 157 D.6.4 Guidelines for Rout usage in echo-cancellers . 158 D.7 Network and service evolutionary considerations . 158 D.7.1 . Communication with switches
35、158 0.7.2 Bit transparency of echo cancellers . 158 0.7.3 Non-linearities in tail circuit 158 D.7.4 Voice compression between tandem cancellers 159 D.7.5 Tandeming of echo cancellers . 159 D.7.6 Convergence speed . 160 D.7.7 Acoustic echo control . 160 D.7.8 New circuit switched service 160 D.7.9 Co
36、mfort noise 180 D.8 Special DCMEPCME networking considerations . 160 0.8.1 Detailed interaction 161 D.8.2 Possible solutions 162 Annex E: A discussion of subjective tests 163 E.l Introduction 163 E.2 Subjective evaluation criteria . 163 E.2.1 Absolute Category Ratings. ACR . 163 E.2.2 “General diffi
37、culty“ -judgement 164 E.2.3 QuantaCResponse Detectability Tests . 164 E.2.4 Degradation Category Rating (DCR) . 165 E.2.5 The threshold method for comparison of transmission systems with a reference . system 165 E.3 Statistical treatment and presentation of results. general . 165 E.4 Handling of sub
38、jective test results . 167 E.4.1 Analysis of results 167 E.4.2 Formats for the presentation of results 168 E.4.3 Comparison of MOS values. obtained from different test occasions or from model computations. by means of linear transformations 168 Annex F: Some examples of voice transmission quality ev
39、aluations by the ETSI model 169 F.l General 169 F.2 Loudness Ratings and electric circuit noise at the O dBr reference point . 170 F.3 Influence of room noise at the send and receive sides . 171 F.4 Listener echo. talker echo and long absolute delay 173 F.5 DCME using ADPCM 32. 24 and 16 kbis 176 F.
40、6 Some examples of connection configurations 176 F.6.1 . Fully analogue connection . 176 F.6.1 . 1 Normal . 176 F.6.1.2 Limiting loss . 177 Digital . analogue connections . 177 F.6.2.1 A fully digital connection with no special impairments . 177 F.6.2.2 A digitaanalogue connection with limiting dela
41、y 178 F.6.2.3 A digital ATM connection . 178 F.6.2 ETSI ETR1250 96 3400855 0330bY 7T0 Page 8 ETR 250: July 1996 F.6.2.4 A mobile (GSM) telephone connected to the PSTN . 178 F.6.2.5 A mobile (GSM) telephone connected to the PSTN via a satellite link . 179 F.6.2.6 F.6.2.7 DECT in a private network 179
42、 F.6.2.8 Private network . 180 DECT intemal system . 179 Annex G: Consideration of low bit-rate codecs in transmission planning . 181 G.l G . 2 G.3 G.4 G.5 G.6 G . 7 G . 8 Introduction . 181 Subjective tests, Mean Opinion Scores (MOS) evaluations . 181 Derivation of the equipment impairment factors
43、/e, general principles . 182 Derivation of the equipment impairment factors /e from the subjective test data . 184 Some comparisons between measured and predicted MOS values 185 Comparison between the “quantizing distortion unit“ qdu and the “equipment impairment factor le . 188 Equipment impairment
44、 factors le to be used in transmission planning 189 Conclusions 189 Annex H: Transmission Quality of Digital Circuit Multiplication Equipment (DCME) 190 H.l Introduction . 190 H.2 Factors affecting transmission quality 190 H.2.1 H.2.2 Encoding process impaimients . 191 H.2.3 Transmission quality ass
45、essment . 191 Interpolation process impairments 190 H.3 Effects of interpolation process 192 Annex J: Usability of telecommunication services; price and quality considerations 193 J.l Some definitions . 193 IS0 Draft document CD 9241-1 1 “Guidance on usability specification and measures“ (2 May 1992
46、) . 193 ETSI enhancements of the definitions 193 J.l.l J.1.2 . J.2 Price and quality considerations . 194 Annex K: Some notes on the verification of the ETSI computation model 195 K.l General . 195 K.2 Formal subjective tests . 196 K.3 Analysis of customer surveys . 196 K.4 Experiences from the use
47、of the model in transmission planning 196 Annex L: Propagation delay and echo control procedures 197 L.l Propagation delay determination in the switching network . 197 L.l.l Availability of propagation delay determination procedures 197 L.1.2 Propagation delay detemination signalling protocol descri
48、ption 197 L.2 Need for a propagation delay determination procedure in the transmission (transport) network . 198 L.3 ETSI ETR*:250 lb 3400855 OL309b5 b37 W Page 9 ETR 250 July 1996 Echo control procedure . 198 L.3.1 . Echo control requirements . 198 L.3.2 Bearer service dependency . 198 L.3.3 End-to
49、-end transmission quality requirements 199 L.3.4 Determination of need for echo cancellers 199 L.3.5 Location of echo control devices . 200 L.3.6 Echo control signalling protocol aspects 200 Annex M: Aspects of voice transmission quality which need further studies 201 M.l M.2 M.3 M.4 M.5 M.6 M.7 Treatment of multiple echoes 201 M.l.l Background 201 M.1.2 Required investigation . 201 Weighting algorithm for acoustic echo paths 201 M.2.1 Background 201 M.2.2 Required investigation . 202 Echo cancellers in conjunction with non-linear echo paths . 202 M.3.1 Backgroun
