Table Of ContentASSESSMENT AND PREDICTION
OF SPEECH QUALITY IN
TELECOMMUNICATIONS
Assessment and Prediction
of Speech Quality in
Telecommunications
by
Sebastian Möller
Institut für Kommunikationsakustik (IKA)
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
A c.I.P. Catalogue record for this book is available from the Library ofCongress.
ISBN 978-1-4419-4989-9 ISBN 978-1-4757-3117-0 (eBook)
DOI 10.1007/978-1-4757-3117-0
Printed on acid-free paper
All Rights Reserved
© 2000 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 2000
Softcover reprint ofthe hardcover 1st edition 2000
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
DES MENSCHEN AUGE HAT NIE GEHÖRT,
DES MENSCHEN OHR NIE GESEHEN;
DES MENSCHEN HAND KANN NICHT SCHMECKEN;
SEINE ZUNGE NICHT BEGREJFEN
NOCH SEIN HERZ BERICHTEN,
WAS MEIN TRAUM WAR.
Ein Sommemach,.'raum. IV. I
Contents
Definitions and Abbreviations Xl
Acknowledgements XVll
Summary XIX
1. INTRODUCTION
2. CONSIDERATIONS ON QUALITY 7
1. Speech Quality 7
2. Quality in the Context of Telecommunications 11
3. FACTORS INFLUENCING THE QUALITY OF SERVICE 17
1. Perceptive Factors 18
1.1 Loudness 19
1.2 Articulation 26
1.3 Effects of Bandwidth Restr. and Frequency Distortion 27
1.4 Perception of Sidetone 28
1.5 Perception of Echo 30
1.6 Perception of Circuit Noise 32
1.7 Perception of Ambient Noise 33
1.8 Effects of Transmission Delay 34
2. Configuration of a Telephone Connection 35
3. Simulation of a Telephone Connection for Quality Assessment
Purposes 38
4. Classification of Transmission and Service Parameters 43
5. Summary 45
4. QUALITY ASSESSMENT IN TELECOMMUNICATIONS 47
1. Choice of Test Subjects 50
2. Articulation and Intelligibility Tests 51
3. Listening-Only and Conversation Opinion Tests 51
3.1 Listening-Only Tests Using Absolute Category Rating 52
3.2 Listening-Only Tests Using Paired Comparison Techn. 54
3.3 Multidimensional Analysis 56
3.4 Talking and Listening Tests 58
vii
viii ASSESSMENT AND PREDICTION OF TELEPHONE-SPEECH QUALITY
3.5 Conversation Tests 59
4. Performance Tests 60
5. User Surveys 61
6. Usability Evaluation 63
7. Assessment of Cost-Related Factors 65
8. Scaling 66
8.1 Ratio Scaling 68
8.2 Absolute Category Scaling 68
8.3 Category-Ratio Scaling 72
9. Development of Conversation Test Scenarios 75
9.1 Requirements for Conversation Test Scenarios 75
9.2 Experiences with two Different Types of Scenario 78
9.3 Scenarios for Special Applications 81
10. Classification of Assessment Methods 85
11. Summary 85
5. MODELS FOR PREDICTING SPEECH COMM. QUALITY AND
SERVICE-RELATED MODELS 89
1. Mouth-to-Ear Models U sing Parameters in the Frequ. Domain 91
2. Mouth-to-Ear Models Using Scalar Parameters 94
2.1 The Additivity Property of the E-Model 96
2.2 Description of the E-Model 99
3. Instrumental Models for Single Transmission Aspects 102
4. Call Set-Up and Call Completion Models 104
5. Customer Behavior Models 108
6. Application and Classification of Prediction Models 109
7. Summary 111
6. RELATIONS BETWEEN FACTORS GOVERNING THE QUALITY
OF SERVICE 115
1. 'Relative' Quality versus 'Absolute' Quality 116
2. References and Normalization 121
3. Assessment in Listening-Only and Conversation Tests 129
4. Expectation 133
5. Influence of the Cost Factor 141
6. Multidimensional Assessment of Voice Transmission Quality 145
7. Existence of an Integral "Psychological Quality Scale" 147
8. Summary 155
7. QUALITY OF PREDICTION MODELS 159
1. Prediction for Single Perceptive Types of Impairment 160
2. Prediction for Combinations of Different Types of Impairment 167
3. Impairment Factor Principle for Low-Bitrate Codecs 172
4. Prediction of Frequency Characteristics 176
5. Measurement of the Input Parameters 184
Contents ix
6. Accuracy of Quality Predictions, Limitations 185
7. Summary 186
8. FINAL DISCUSSION AND CONCLUSIONS 189
Appendices 197
A- Glossary 197
B- Perceptive Characteristics 199
Resulting from New Technologies
1. Impact of New Technologies and Equipment 199
2. Classification for Modeling Purposes 201
C- Discussion of Articulation and Intelligibility Test 205
Methodologies
D- Graeco-Latin-Square Test Design 207
E- SCT Scenarios 209
I. Examples of SCT Scenarios 209
2. Explanations of the SCT Dialog Structure Given to the Test
Subjects 213
F- Closing Questionnaire Given after Laboratory Tests 215
G- E-Model Algorithm 217
H- Test Conditions and Results 221
1. Test Conditions of the Isopreference Test 221
2. Relation between E-Model Predictions and Test Results 222
3. Comparison of SUBMOD Model Predictions and Test Results 225
Bibliography 227
Index
241
Definitions and Abbreviations
Definitions
expectation factor
factor for calculating LOI, depending on the loudness of re
ceived speech
Aw warping amplitude
a,b constants of the 'power law'
B' frequency weighting function related to loudness
B~ frequency weighting function related to articulation
B~E frequency weighting function related to listening-effort
bo description of an auditory event
ßo pure tone threshold ofhearing in quiet [dB rel. 20 J.LPaoHz-1/2]
ß's spectrum density of speech at MRP [dB Tel. 20 J.LPaoHz-1/2]
D frequency-weighted version of DELSM
factor for ca1culating LOI, depending on the level of circuit
DLOI
noise
d magnitude of a stimulus
dM magnitude of a stimulus at the midopinion value of the scale
DELSM frequency--dependent difference in sensitivity between the di
rected and diffuse sound [dB]
%Diff percentage of users experiencing difficulty in talking or listen
ing over a connection
J, fk frequency [Hz]
F sampling frequency [Hz]
s
Fw warping frequency [Hz]
(f).f)c bandwidth of critical band [Hz]
G signal-to-equivalent-continuous-circuit-noise ratio [dB]
9 exponent of the logistic psychometric function
GL frequency weighting function for the ca1culation of loudness
ratings
%GoB percentage of users rating a connection good or better
ho auditory event
I,Itot impairment factor
Id impairment factor for delayed impairments related to the
speech signal
Ie equipment impairment factor
Iq impairment factor for quantizing distortion
18 impairment factor for impairments occurring simultaneously
with the speech signal
Xl
XlI ASSESSMENT AND PREDICTION OF TELEPHONE-SPEECH QUALITY
IQoS GSM quality of service index
K factor for calculating Yc from YLE
k exponent of the relation between subjective rating and
apparent magnitude
Kc allowance to the threshold of hearing of complex tones in
quiet [dB]
frequency weighting function for alternatively calculating
loudness ratings
point of maximum excitation on the basilar membrane
measured from the helicotrema due to atone at fk [mm]
totallength of the basilar membrane [mm]
lmax
Le frequency-dependent loss of the talker echo path [dB]
Lst frequency-dependent loss of the sidetone path [dB]
LME, LRME, air-to-air transmission loss from mouth reference point
to ear reference point [dB]
LUME
L RME, LUME weighted average mouth-to-ear loss [dB]
A, AR, AU impression of loudness
LOI listening opinion index
LSTR listener sidetone rating [dB]
Lo constant factor for calculating loudness ratings
(ßl)c criticallength [mm]
M shift in hearing threshold attributable to the presence of
noise [dB]
m exponent of the growth function Q(Z)
mse mean squared error
n(k) sampled noise signal
N total number of frequency bands for calculating loudness
ratings
Ne circuit noise level [dBmOp]
Nfor noise floOf level [dBmp]
Np perceptual magnitude
No total equivalent circuit noise level [dBmOp]
OLR overallloudness rating between MRP and ERP [dB]
P,Pr, Ps mean normalized opinion for an impairment
P(Z) growth function of Z related to listening-effort
Pa(Z) growth function of Z related to articulation
Pr A-weighted sound pressure level of room noise at receive
side [dB(A)]
Ps A-weighted sound press ure level of room noise at send
side [dB(A)]
%PoW percentage of users rating a connection poor or worse
Q signal-to-quantizing-noise ratio [dB]
Definitions and Abbreviations X111
Q(Z) growth function of Z related to loudness
qdu quantizing distortion unit
r Pearson correlation coefficient
R transmission rating
Ree transmission rating taking into account call-completion im
pairments
Res transmission rating taking into account call-setup impair
ments
transmission rating taking into account loss, noise and talker
echo
R' weighted sound reduction index [dB]
w
Ro basic signal-to-noise transmission rating factor
RLR receive loudness rating between the 0 dBr point in the network
and the ERP [dB]
RLRset receive loudness rating of the telephone handset [dB]
So sound event
electro-acoustic receiving sensitivity from junction to ERP
SJE
[dB]
acousto-electric sending sensitivity from MRP to junction
[dB]
air-to-air sensitivity ofthe electric sidetone path for directed
SmeST
(speech) sound, as defined in ITU-T Rec. P.64 (1997) [dB]
air-to-air sensitivity of the electric sidetone path for diffuse
SRNST
(room noise) sound, as defined in ITU-T Rec. P.64 (1997)
[dB]
SLR send loudness rating between the MRP and the 0 dBr point in
the network [dB]
SLRset send loudness rating of the telephone handset [dB]
STMR sidetone masking rating [dB]
t level of sensation on a continuous finite rating scale
T mean one-way talker echo path delay [ms]
Ta overall delay between MRP of the talker and ERP of the Iis
tener [ms]
Tr round-trip delay for listener echo [ms]
TELR talker echo loudness rating [dB]
%TME percentage of users terminating a call early
Ve, VL active speech level in conversation or Iistening-only situa
tions [dBV]
Wi frequency weighting function for calculating loudness ratings
WEPL weighted echo path 10ss for Iistener echo [dB]
x(k) sampled input signal
