SIST EN IEC 60268-16:2021

SLOVENSKI STANDARD
SIST EN IEC 60268-16:2021
01-julij-2021
Nadomešča:
SIST EN 60268-16:2011
Oprema za zvokovne sisteme - 16. del: Objektivno ocenjevanje govorne
razumljivosti z uporabo indeksa prenosa govora (IEC 60268-16:2020)
Sound system equipment - Part 16: Objective rating of speech intelligibility by speech
transmission index (IEC 60268-16:2020)
Elektroakustische Geräte - Teil 16: Objektive Bewertung der Sprachverständlichkeit
durch den Sprachübertragungsindex (IEC 60268-16:2020)
Equipements pour systèmes électroacoustiques - Partie 16: Evaluation objective de
l'intelligibilité de la parole au moyen de l'indice de transmission de la parole (IEC 60268-
16:2020)
Ta slovenski standard je istoveten z: EN IEC 60268-16:2020
ICS:
33.160.30 Avdio sistemi Audio systems
SIST EN IEC 60268-16:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 60268-16:2021

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SIST EN IEC 60268-16:2021


EUROPEAN STANDARD EN IEC 60268-16

NORME EUROPÉENNE

EUROPÄISCHE NORM
November 2020
ICS 33.160.01 Supersedes EN 60268-16:2011 and all of its
amendments and corrigenda (if any)
English Version
Sound system equipment - Part 16: Objective rating of speech
intelligibility by speech transmission index
(IEC 60268-16:2020)
Équipements pour systèmes électroacoustiques - Partie 16: Elektroakustische Geräte - Teil 16: Objektive Bewertung der
Évaluation objective de l'intelligibilité de la parole au moyen Sprachverständlichkeit durch den Sprachübertragungsindex
de l'indice de transmission de la parole (IEC 60268-16:2020)
(IEC 60268-16:2020)
This European Standard was approved by CENELEC on 2020-10-30. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.


European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN IEC 60268-16:2020 E

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SIST EN IEC 60268-16:2021
EN IEC 60268-16:2020 (E)
European foreword
The text of document 100/3202/CDV, future edition 5 of IEC 60268-16, prepared by IEC/TC 100
"Audio, video and multimedia systems and equipment" was submitted to the IEC-CENELEC parallel
vote and approved by CENELEC as EN IEC 60268-16:2020.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2021-07-30
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2023-10-30
document have to be withdrawn
This document supersedes EN 60268-16:2011 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 60268-16:2020 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 60318-1:2009 NOTE Harmonized as EN 60318-1:2009 (not modified)
IEC 61672-1 NOTE Harmonized as EN 61672-1
IEC 60118-4 NOTE Harmonized as EN 60118-4
ISO 9921:2003 NOTE Harmonized as EN ISO 9921:2003 (not modified)
ISO/TR 22411:2008 NOTE Harmonized as CEN ISO/TR 22411:2011 (not modified)
ISO 3382-1:2009 NOTE Harmonized as EN ISO 3382-1:2009 (not modified)
2

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SIST EN IEC 60268-16:2021
EN IEC 60268-16:2020 (E)
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 61260-1 2014 Electroacoustics - Octave-band and fractional- EN 61260-1 2014
octave-band filters - Part 1: Specifications

3

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SIST EN IEC 60268-16:2021




IEC 60268-16

®


Edition 5.0 2020-09




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE
colour

inside










Sound system equipment –

Part 16: Objective rating of speech intelligibility by speech transmission index



Équipements pour systèmes électroacoustiques –

Partie 16: Evaluation objective de l'intelligibilité de la parole au moyen

de l'indice de transmission de la parole















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 33.160.01 ISBN 978-2-8322-8862-7




Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 12
2 Normative references . 12
3 Terms and definitions . 12
4 Description of the STI model. 18
4.1 Overview. 18
4.2 Applicability of the STI model . 19
4.3 Theoretical details . 19
4.3.1 Envelope function and envelope spectrum . 19
4.3.2 Reduction of modulation . 20
4.3.3 Role of the octave-band noise carriers . 20
4.3.4 Theoretical overview . 20
4.4 Measurement of STI . 22
4.4.1 Direct and indirect methods . 22
4.4.2 Full STI . 23
4.4.3 STIPA . 23
4.4.4 Choice of method . 23
5 Direct method of measuring STI – User guidance . 25
5.1 Overview. 25
5.2 STIPA . 26
5.3 Application . 26
5.4 Limitations . 26
6 Indirect method of measuring STI (impulse response) – User guidance . 27
6.1 Overview. 27
6.2 Application . 27
6.3 Limitations (non-linear distortion) . 28
7 Limitations of the STI model . 29
7.1 General . 29
7.2 Frequency shifts . 30
7.3 Centre clipping . 30
7.4 Dropouts . 30
7.5 Jitter . 30
7.6 Digital voice compression systems . 30
7.7 Overestimation of STI under low background noise conditions . 31
7.8 Frequency response . 31
7.9 Echoes . 32
7.10 Fast amplitude compression and expansion . 34
7.11 Non-linear distortion. 35
7.12 Hearing impaired listeners . 35
7.13 Impulsive and fluctuating noise . 35
7.14 Conclusion . 35
8 Measurement procedures, post-processing of data and applications . 36
8.1 General . 36
8.2 Acoustical input . 36

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8.3 Acoustical output . 38
8.4 Electrical input . 38
8.5 Electrical output . 38
8.6 Examples of input/output combinations . 38
8.6.1 Acoustical input – Acoustical output . 38
8.6.2 Electrical input – Electrical output (e.g. assessment of wired and
wireless) communication systems) . 38
8.6.3 Acoustical input – Electrical output (e.g. assessment of microphones) . 38
8.6.4 Electrical input – Acoustical output (e.g. assessment of PA systems) . 39
8.7 Spatial averaging of STI measurements . 39
8.8 Post-processing of measured MTF data . 40
8.9 Issues concerning noise . 40
8.9.1 General . 40
8.9.2 Measurement of background noise . 41
8.9.3 Fluctuating noise . 41
8.10 Analysis and interpretation of the results. 41
8.11 Binaural STI measurements . 42
9 Use of the STI as a design prediction tool . 42
9.1 Overview. 42
9.2 Statistical predictions . 43
9.3 Prediction from simulated impulse response . 43
Annex A (informative) The basis of the STI concept . 44
A.1 Introduction to this annex . 44
A.1.1 Purpose . 44
A.1.2 Modulation transfer function (MTF) . 44
A.1.3 STI model . 45
A.1.4 STI modulation frequencies . 46
A.2 Calculation of the STI . 46
A.2.1 General equation for STI . 46
A.2.2 Gender-specific octave band weighting and redundancy factors . 47
A.2.3 Adjustment of the MTF for ambient noise . 48
A.2.4 Adjustment of the MTF for auditory masking and threshold effects . 48
A.3 Calculation of the modulation transfer ratio values . 49
A.3.1 Direct method: Analysis of the STI test signal . 49
A.3.2 Indirect method: Determination of the modulation transfer
function (MTF) . 50
A.4 Auditory effects on the STI . 51
A.4.1 Overview . 51
A.4.2 Level-dependent auditory masking. 51
A.4.3 Absolute speech reception threshold . 54
A.5 Generation of the STI test signal (direct method) . 54
A.5.1 Pink noise source signal . 54
A.5.2 Generating octave band carrier signals . 54
A.5.3 Intensity modulation of the carrier signals . 55
A.5.4 Applying the speech spectrum to the STI test signal . 55
A.6 Spectrum of STI test signal . 55
A.6.1 Standardized speech spectrum . 55
A.6.2 Speech-shaped noise . 55
Annex B (normative) STIPA method . 57

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B.1 Overview. 57
B.2 Test signal . 57
Annex C (normative) Verification of STI measuring devices . 59
C.1 Specification of the measuring device . 59
C.2 Signals for testing STI implementations . 59
C.3 Testing the dynamic range in the modulation domain . 59
C.3.1 General . 59
C.3.2 Modulation depth testing for STIPA direct method . 59
C.3.3 Modulation depth testing for STI indirect method . 60
C.4 Testing of cross-talk between octave-band filters . 61
C.4.1 Flank attenuation slopes . 61
C.4.2 Octave band filter testing – STIPA direct method . 61
C.4.3 Performance verification files . 62
Annex D (informative) Use of STI measuring devices . 63
D.1 Overview. 63
D.2 STIPA characterises only the speech transmission channel . 63
D.3 Examples of test scenarios for STIPA tests . 64
D.4 Equipment and resources needed for a STIPA test . 67
D.4.1 Availability of the test signal . 67
D.4.2 A source of the STIPA test signal . 67
D.4.3 A STIPA analyser . 67
D.5 Steps in the overall procedure . 67
Annex E (informative) Qualification of the STI and relationships with other speech
intelligibility measures . 68
E.1 Relationship between the STI and word/sentence scores . 68
E.2 Relationship between STI and listening difficulty . 68
Annex F (informative) Nominal qualification bands for STI . 70
Annex G (informative)  Examples of STI qualification bands and typical applications . 71
Annex H (informative) Non-native listeners . 72
Annex I (informative) Effect of age-related hearing loss and hearing impairment on
speech intelligibility . 73
Annex J (normative) Setting and adjustment of STI test signal level . 74
J.1 Overview. 74
J.2 The concept of 'speech level' and the method of measurement . 74
J.3 Real speech level . 74
J.4 Corrected speech level derived from real speech level . 75
J.5 Comparison of dynamic structures of speech and test signals . 75
Annex K (informative) Example test report sheet for STI measurements . 77
Annex L (normative) Prediction of the STI using statistical methods . 79
Annex M (informative) Adjustments to STI data to simulate alternative ambient noise
spectra and different speech levels . 81
Annex N (informative) Other methods of determining speech intelligibility . 91
N.1 Overview. 91
N.2 Word tests . 91
N.3 Modified rhyme tests . 91
N.4 Speech intelligibility index (SII) . 92
N.5 PESQ . 92
Annex O (informative) Alternative direct methods for measuring Full STI . 93

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Annex P (normative) Information to be provided by manufacturers . 94
P.1 Purpose of this annex . 94
P.2 Form in which the information is to be provided . 94
P.3 Required information . 94
P.4 Declaration . 94
Annex Q (informative) Effect of uncertainties of selected parameters on STI
uncertainty . 95
Q.1 STI calculation framework . 95
Q.1.1 Overview . 95
Q.1.2 Statistical MTF. 95
Q.1.3 Corrections . 95
Q.1.4 Effective SNR . 96
Q.1.5 Modulation transfer index (MTI) . 96
Q.1.6 Speech transmission index (STI) . 96
Q.2 The effect of RT uncertainty on STI uncertainty . 97
Q.2.1 General . 97
Q.2.2 Modulation transfer function. 97
Q.2.3 Uncertainty in the STI . 97
Q.2.4 Conclusions: . 99
Q.3 The effect of S/N uncertainty on STI uncertainty . 99
Q.3.1 General . 99
Q.3.2 Ideal transfer function . 99
Q.3.3 Reverberation . 100
Q.3.4 Conclusions: . 101
Q.4 The effect of signal level uncertainty on STI uncertainty . 101
Q.4.1 Overview . 101
Q.4.2 Auditory masking . 101
Q.4.3 Conclusions . 103
Bibliography . 104

Figure 1 – Envelope function (panel A) of a 10 s speech signal for the 250 Hz octave
band and corresponding envelope spectrum (panel B) . 20
Figure 2 – Modulation transfer function – Input/output comparison . 21
Figure 3 – Effect of a single delayed arrival on the MTF (idealised conditions) . 33
Figure 4 – Idealised STI (Male speech Spectrum) versus delay and level of secondary
arrival . 34
Figure A.1 – Theoretical expression of the MTF . 44
Figure A.2 – Measurement system and frequencies for the STI method . 46
Figure A.3 – Auditory masking of octave band (k–1) on octave band (k) . 52
Figure A.4 – Relationship between STI and speech level for different reverberation
times. 53
Figure D.1 – Schematic representation of the definition of a speech transmission
channel . 64
Figure E.1 – Relationships between some speech intelligibility measures . 68
Figure E.2 – Relationship between STI, speech intelligibility scores and listening
difficulty ratings [43], [44] . 69
Figure F.1 – STI qualification bands . 70

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Figure Q.1 – Uncertainty in absolute value of STI vs reverberation time RT with
various degrees of uncertainty in RT . 99
Figure Q.2 – Uncertainty in absolute value of STI vs reverberation time RT with 1 dB

uncertainty in SNR at various SNRs . 101
Figure Q.3 – Uncertainty in absolute value of STI versus reverberation time RT with
various degrees of masking. .
...