SIST EN 60268-16:2011
(Main)Sound system equipment - Part 16: Objective rating of speech intelligibility by speech transmission index (IEC 60268-16:2011)
Sound system equipment - Part 16: Objective rating of speech intelligibility by speech transmission index (IEC 60268-16:2011)
This part of IEC 60268 specifies objective methods for rating the transmission quality of
speech with respect to intelligibility.
The objective of this standard is to provide a comprehensive manual for all types of users of
the STI method in the fields of audio, communications and acoustics.
This standard does not provide STI criteria for certification of transmission channels (e.g.
criteria for a voice-alarm system).
Three methods are presented, which are closely related and are referred to as STI, STIPA,
and STITEL. The first two methods are intended for rating speech transmission performance
with or without sound systems. The STITEL method has more restricted uses.
NOTE None of the methods are suitable for the measurement and assessment of speech privacy and speech
masking systems, as STI has not been validated for conditions that represent speech privacy applications [1]1.
The following information is included:
• measurement techniques;
• prediction techniques.
Elektroakustische Geräte - Teil 16: Objektive Bewertung der Sprachverständlichkeit durch den Sprachübertragungsindex (IEC 60268-16:2011)
Equipements pour systèmes électroacoustiques - Partie 16: Evaluation objective de l'intelligibilité de la parole au moyen de l'indice de transmission de la parole (CEI 60268-16:2011)
La CEI 60268-16:2011 spécifie des méthodes objectives d'évaluation de la qualité de transmission de la parole sous l'angle de l'intelligibilité. Elle met un manuel complet à la disposition de tous les types d'utilisateurs de la méthode STI dans les domaines de l'audio, des communications et de l'acoustique. Trois méthodes, étroitement liées, sont présentées sous le nom de STI, STIPA, et STITEL. Les deux premières méthodes sont destinées à l'évaluation des performances de la transmission de la parole avec ou sans systèmes électroacoustiques. La méthode STITEL a des utilisations plus restreintes. Cette quatrième édition annule et remplace la troisième édition parue en 2003, et constitue une révision technique. Elle inclut les modifications techniques importantes suivantes par rapport à l'édition précédente:
- Le développement d'une normalisation plus aboutie, plus complète et moins ambiguë de la méthodologie STI;
- le terme STIr n'est plus utilisé. Une nouvelle fonction pour la prédiction des effets du masquage auditif est introduite;
- le concept de "niveau de parole" et le réglage du niveau du signal d'essai ont été introduits;
- des informations supplémentaires relatives aux modes opératoires de prédiction et de mesures ont été incluses. La version française de cette norme n'a pas été soumise au vote.
Oprema za zvokovne sisteme - 16. del: Objektivno ocenjevanje govorne razumljivosti z uporabo indeksa prenosa govora (IEC 60268-16:2011)
Ta del IEC 60268 določa objektivne metode za ocenjevanje kakovosti prenosa govora z zvezi z razumljivostjo.
Cilj tega standarda je zagotoviti celosten priročnik za vse vrste uporabnikov
metode STI pri slušnosti komunikaciji in akustiki.
Ta standard ne zagotavlja kriterijev STI za certifikacijo kanalov prenosa (npr. kriterijev za sistem glas-alarm).
Predstavljene so tri metode, ki so tesno povezane in so omenjene kot STI, STIPA in STITEL. Prvi dve metodi sta namenjeni ocenjevanju delovanja prenosa govora
z zvokovnimi sistemi ali brez njih.
Uporabe metode STITEL so bolj omejene.
OPOMBA: Nobena izmed teh metod ni primerna za merjenje in ocenitev zasebnosti govora in sistemov za maskiranje govora, ker STI ni bil potrjen za zahteve, ki predstavljajo uporabe za zasebnost govora [1]1.
Vključene so naslednje informacije:
• tehnike merjenja;
• tehnike napovedovanja.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 60268-16:2011
01-november-2011
1DGRPHãþD
SIST EN 60268-16:2003
Oprema za zvokovne sisteme - 16. del: Objektivno ocenjevanje govorne
razumljivosti z uporabo indeksa prenosa govora (IEC 60268-16:2011)
Sound system equipment - Part 16: Objective rating of speech intelligibility by speech
transmission index (IEC 60268-16:2011)
Elektroakustische Geräte - Teil 16: Objektive Bewertung der Sprachverständlichkeit
durch den Sprachübertragungsindex (IEC 60268-16:2011)
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Ta slovenski standard je istoveten z: EN 60268-16:2011
ICS:
33.160.30 Avdio sistemi Audio systems
SIST EN 60268-16:2011 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 60268-16:2011
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SIST EN 60268-16:2011
EUROPEAN STANDARD
EN 60268-16
NORME EUROPÉENNE
August 2011
EUROPÄISCHE NORM
ICS 33.160.01 Supersedes EN 60268-16:2003
English version
Sound system equipment -
Part 16: Objective rating of speech intelligibility by speech transmission
index
(IEC 60268-16:2011)
Equipements pour systèmes Elektroakustische Geräte -
électroacoustiques - Teil 16: Objektive Bewertung der
Partie 16: Evaluation objective de Sprachverständlichkeit durch den
l'intelligibilité de la parole au moyen de Sprachübertragungsindex
l'indice de transmission de la parole (IEC 60268-16:2011)
(CEI 60268-16:2011)
This European Standard was approved by CENELEC on 2011-08-02. 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 Central Secretariat 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 Central Secretariat 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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60268-16:2011 E
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SIST EN 60268-16:2011
EN 60268-16:2011 - 2 -
Foreword
The text of document 100/1812/FDIS, future edition 4 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 was
approved by CENELEC as EN 60268-16 on 2011-08-02.
This European Standard supersedes EN 60268-16:2003.
EN 60268-16:2011 includes the following technical changes with respect to EN 60268-16:2003:
— development of more comprehensive, complete and unambiguous standardization of the STI
methodology;
— the term STI is discontinued. A new function for the prediction of auditory masking effects is
r
introduced;
— the concept of 'speech level' and the setting of the level of the test signal have been introduced;
— additional information has been included on prediction and measurement procedures.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2012-05-02
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2014-08-02
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60268-16:2011 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:
[2] IEC 60318-1:2009 NOTE Harmonized as EN 60318-1:2009 (not modified).
[3] IEC 61672 series NOTE Harmonized in EN 61672 series.
[37] ISO 7029:2000 NOTE Harmonized as EN ISO 7029:2000.
[44] ISO 3382-1:2009 NOTE Harmonized as EN ISO 3382-1:2009.
__________
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SIST EN 60268-16:2011
- 3 - EN 60268-16:2011
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application 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 When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year
IEC 61260 1995 Electroacoustics - Octave-band EN 61260 1995
+ A1 2001 and fractional-octave-band filters + A1 2001
ISO 18233 2006 Acoustics - Application of new EN ISO 18233 2006
measurement methods in building and room
acoustics
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SIST EN 60268-16:2011
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SIST EN 60268-16:2011
IEC 60268-16
®
Edition 4.0 2011-06
INTERNATIONAL
STANDARD
Sound system equipment –
Part 16: Objective rating of speech intelligibility by speech transmission index
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 33.160.01 ISBN 978-2-88912-522-7
® Registered trademark of the International Electrotechnical Commission
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SIST EN 60268-16:2011
– 2 – 60268-16 IEC:2011(E)
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Description of the STI method . 15
4.1 General . 15
4.1.1 Rationale for the STI method . 15
4.1.2 Applicability of the STI method . 15
4.2 Background of the STI method . 16
4.2.1 General . 16
4.2.2 Theoretical overview . 17
4.2.3 Measurement of STI . 18
4.3 Applicability of STI test methods . 19
4.4 Use of direct and indirect methods . 20
4.5 Limitations of the STI method . 21
4.5.1 General . 21
4.5.2 Frequency shifts . 21
4.5.3 Centre clipping . 22
4.5.4 Drop outs . 22
4.5.5 Jitter . 22
4.5.6 Vocoders . 22
4.5.7 Overestimation of STI under low background noise conditions . 22
4.5.8 Frequency response . 22
4.5.9 Echoes . 23
4.5.10 Fast amplitude compression and expansion . 23
4.5.11 Non-linear distortion . 24
4.5.12 Impulsive and fluctuating noise . 24
4.5.13 Hearing impaired listeners . 24
4.6 Conclusion . 24
5 Direct method of measuring STI . 24
5.1 Overview . 24
5.2 STIPA . 25
5.3 Application . 26
5.4 Limitations . 26
6 Indirect method of measuring STI using the impulse response . 26
6.1 Overview . 26
6.2 Application . 27
6.3 Limitations (non-linear distortion) . 28
7 Measurement procedures, post-processing of data and applications . 28
7.1 General . 28
7.2 Acoustical input . 28
7.3 Acoustical output . 30
7.4 Electrical input . 30
7.5 Electrical output . 30
7.6 Examples of input/output combinations. 30
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SIST EN 60268-16:2011
60268-16 IEC:2011(E) – 3 –
7.6.1 Acoustical input – Acoustical output . 30
7.6.2 Electrical input – Electrical output (e.g. assessment of wired and
wireless) communication systems) . 30
7.6.3 Acoustical input – Electrical output (e.g. assessment of microphones) . 31
7.6.4 Electrical input – Acoustical output (e.g. assessment of PA systems) . 31
7.7 Post-processing of measured MTF data . 31
7.8 Issues concerning noise . 31
7.8.1 General . 31
7.8.2 Measurement of background noise . 32
7.8.3 Fluctuating noise . 32
7.9 Analysis and interpretation of the results . 32
7.10 Binaural STI measurements . 33
8 Use of STI as a design prediction tool . 33
8.1 Overview . 33
8.2 Statistical predictions . 33
8.3 Prediction from simulated impulse response . 34
Annex A (normative) Speech transmission index (STI) and revised STI methods . 35
Annex B (normative) STIPA method . 47
Annex C (normative) STITEL method . 48
Annex D (informative) RASTI method (obsolete) . 49
Annex E (informative) Qualification of the STI and relationships with other speech
intelligibility measures. 51
Annex F (informative) Nominal qualification bands for STI . 53
Annex G (informative) Examples of STI qualification bands and typical applications . 54
Annex H (informative) Non-native listeners . 55
Annex I (informative) Effect of age-related hearing loss and hearing impairment on
speech intelligibility. 56
Annex J (normative) Calibration of STI test signal level . 57
Annex K (informative) Example test report sheet for STI measurements . 59
Annex L (normative) Prediction of STI using statistical methods . 61
Annex M (informative) Adjustments to measured STI and STIPA results for simulation
of occupancy noise and different speech levels . 63
Annex N (informative) Other methods of determining speech intelligibility . 67
Bibliography . 69
Figure 1 – Concept of the reduction in modulation due to a transmission channel . 16
Figure 2 – Modulation transfer function – Input/output comparison . 17
Figure A.1 – Envelope function (panel A) of a 10 s speech signal for the 250 Hz
octave band and corresponding envelope spectrum (panel B) . 35
Figure A.2 – Theoretical expression of the MTF . 36
Figure A.3 – Measurement system and frequencies for the STI method . 38
Figure A.4 – Auditory masking of octave band (k – 1) on octave band (k) . 39
Figure D.1 – Illustration of a practical RASTI test signal . 50
Figure E.1 – Relationships between some speech intelligibility measures . 51
Figure E.2 – Relationship between STI, speech intelligibility scores and listening
difficulty ratings [34], [35] . 52
Figure F.1 – STI qualification bands . 53
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SIST EN 60268-16:2011
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Table 1 – Comparison of STI test methods for different types of distortion . 19
Table 2 – Applicability of test . 20
Table 3 – Choice of method . 21
Table A.1 – Auditory masking as a function of the octave band level. 40
Table A.2 – Absolute speech reception threshold level in octave bands . 41
Table A.3 – MTI octave band weighting factors . 41
Table A.4 – Octave band levels (dB) relative to the A-weighted speech level . 42
Table B.1 – Modulation frequencies for the STIPA method . 47
Table C.1 – Modulation frequencies for the STITEL method . 48
Table D.1 – Modulation frequencies for the RASTI method . 49
Table E.1 – Categories for listening difficulty . 52
Table G.1 – Examples between STI qualification bands and typical applications . 54
Table H.1 – Adjusted intelligibility qualification tables for non-native listeners . 55
Table I.1 – Adjusted intelligibility qualification tables for normal listeners and people
over 60 years old with hearing loss . 56
Table M.1 – Example calculation . 63
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SIST EN 60268-16:2011
60268-16 IEC:2011(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SOUND SYSTEM EQUIPMENT –
Part 16: Objective rating of speech intelligibility
by speech transmission index
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60268-16 has been prepared by IEC technical committee 100:
Multimedia equipment and systems.
This fourth edition cancels and replaces the third edition, published in 2003, and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• development of more comprehensive, complete and unambiguous standardization of the
STI methodology;
• the term STI is discontinued. A new function for the prediction of auditory masking effects
r
is introduced;
• the concept of ‘speech level’ and the setting of the level of the test signal have been
introduced;
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SIST EN 60268-16:2011
– 6 – 60268-16 IEC:2011(E)
• additional information has been included on prediction and measurement procedures.
NOTE See Introduction for a historical summary referring to the various changes from the first to the fourth
edition (current edition).
The text of this standard is based on the following documents:
FDIS Report on voting
100/1812/FDIS 100/1849/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60268 series, published under the general title Sound system
equipment can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
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SIST EN 60268-16:2011
60268-16 IEC:2011(E) – 7 –
INTRODUCTION
The Speech Transmission Index (STI) is an objective measure to predict the intelligibility of
speech transmitted from talker to listener by a transmission channel. The STI method has
been the subject of ongoing development and refinement since its introduction in the 1970s.
Major improvements of the STI have been consolidated by incorporating them in successive
revisions of IEC 60268-16.
The history of revisions is as follows.
• Revision 1: 1988. In the first version of the STI standard, a gender-independent test
signal spectrum was used.
• Revision 2: 1998. Gender specific test signals were introduced, for male and female
talkers, each gender relating to a specific set of weighting factors. In addition, weightings
were introduced for redundancy factors. The term STI was introduced to signify the use of
r
these redundancy factors.
• Revision 3: 2003. Important differences between Revision 2 and Revision 3 are the
introduction of
− level dependent masking functions,
− the STI derivative STIPA.
STIPA was specially developed as a fast measurement method that could deal with
electro-acoustic and acoustic effects while determining the speech transmission quality of
PA systems.
• Revision 4: 2010. The aim of Revision 4 (this revision) is to provide a more
comprehensive, complete and unambiguous standardization of the STI methodology. The
term STI is now discontinued. A new function for the prediction of auditory masking
r
effects is introduced.
Speech is considered to be the major method of communication between humans. In many
situations the speech signal is degraded by the signal path or the transmission channel
between talker and listener, resulting in a reduction of the intelligibility of the speech at the
listener’s location.
To quantify the deterioration of the speech intelligibility induced by the transmission channel,
a fast and objective measuring method was developed; the Speech Transmission Index (STI).
The STI method applies a specific test signal to the transmission channel and by analysing
the received test signal; the speech transmission quality of the channel is derived and
expressed in a value between 0 and 1, as the Speech Transmission Index (STI). Using the
obtained STI-value, the potential speech intelligibility can be determined.
Although there are limitations to the STI method, the use of STI has proved useful in many
situations and has gained international acceptance.
Items that have changed in this revision
Specific changes that have been incorporated in this revision are:
• refinement of the STI model with respect to the level dependent masking function;
• Room Acoustic Speech Transmission Index (RASTI) has become obsolete and should not
be used;
• calculations to add or remove the effects of background noise and to change the speech
level and a worked example;
• notes regarding limitations of the STI method;
• methods to predict the STI performance of transmission channels based on the predicted
(as distinct from measured) performance of parts or all of the transmission channel;
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SIST EN 60268-16:2011
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• introduction of STI corrections for non-native language listeners;
• introduction of STI corrections for listeners with some specific forms of hearing loss;
• relationships between STI and ‘Listening Difficulty’ scale.
Potential applications of STI
STI may be used to measure the potential intelligibility of a wide range of electronic systems
and acoustic environments. Typical applications include:
• measurement of Public Address and Sound Reinforcement Systems;
• measurement and Certification of Voice Alarm and emergency sound systems;
• measurement of communication channels / systems such as intercoms and wireless
communication;
• measurement of potential speech intelligibility and communication in rooms and auditoria;
• evaluation of direct speech communication (situations without electronic amplification) in
rooms or acoustic spaces including vehicles;
• evaluation of the potential intelligibility of Assistive Hearing Systems;
NOTE The STI method is not validated for the measurement and evaluation of speech privacy or speech masking
systems.
Potential users of STI
The range of users of STI measurements is diverse. Among the users who may apply this
method are:
• certifiers of voice alarm and other types of emergency systems;
• certifiers of sound reinforcement and audio systems;
• audio and telecommunication equipment manufacturers;
• audio and communication engineers;
• acoustical and electro-acoustical engineers;
• sound system installers;
• researchers into STI methods and developers of instruments to measure STI.
To avoid misinterpretation of STI results, it is important that all users have an understanding
of the basic principles, the application domain and its limitations.
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