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BS EN IEC 60268-16:2020

BS EN IEC 60268-16:2020

$215.11

Sound system equipment – Objective rating of speech intelligibility by speech transmission index

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BSI 2020 114
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IEC 60268-16:2020 defines the STI model, test signals, measurement and prediction methods. The objective of this document is to provide a comprehensive manual for all types of users of the STI model in the fields of audio, communications and acoustics. This document does not provide STI criteria for certification of transmission channels (e.g. criteria for a voice-alarm system), but some typical application values are provided in Annex G. Every measurement method has limitations, and the reader is referred to clauses relating to limitations such as speech privacy, echo and systems using digital voice compression (vocoders).This document does not cover the case of fluctuating noise on the STI, although some general comments on dealing with this complex issue are provided in 7.13 and 8.9.3. IEC 60268-16:2020 cancels and replaces the fourth edition published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) the spectrum of the male speech test signal has been changed, with significant reductions in the 125 Hz and 250 Hz bands being implemented; b) some corrections to formulae have been made; c) additional information has been included on prediction and measurement procedures; d) spectrum and weighting factors for female speech have been removed; e) verification information for STI measurement devices added; f) the relationships between STI and number of other speech intelligibility measures have been updated in Annex E;g) greater information is given in Annex M about adjustments to the measured STI results to simulate effects of alternative ambient noise and speech levels.

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PDF Pages PDF Title
2 undefined
5 Annex ZA(normative)Normative references to international publicationswith their corresponding European publications
7 English
CONTENTS
12 FOREWORD
14 INTRODUCTION
15 Tables
Table 1 – How to use this document
17 1 Scope
2 Normative references
3 Terms and definitions
23 4 Description of the STI model
4.1 Overview
24 4.2 Applicability of the STI model
4.3 Theoretical details
4.3.1 Envelope function and envelope spectrum
25 4.3.2 Reduction of modulation
4.3.3 Role of the octave-band noise carriers
4.3.4 Theoretical overview
Figures
Figure 1 – Envelope function (panel A) of a 10 s speech signal for the 250 Hz octave band and corresponding envelope spectrum (panel B)
26 Figure 2 – Modulation transfer function – Input/output comparison
27 4.4 Measurement of STI
4.4.1 Direct and indirect methods
Table 2 – Comparison of direct and indirect methods
28 4.4.2 Full STI
4.4.3 STIPA
4.4.4 Choice of method
29 Table 3 – Suitability of STI test methods for different types of distortion
Table 4 – Test-method suitability
30 5 Direct method of measuring STI – User guidance
5.1 Overview
Table 5 – Measurement applications
31 5.2 STIPA
5.3 Application
5.4 Limitations
32 6 Indirect method of measuring STI (impulse response) – User guidance
6.1 Overview
6.2 Application
33 6.3 Limitations (non-linear distortion)
34 7 Limitations of the STI model
7.1 General
35 7.2 Frequency shifts
7.3 Centre clipping
7.4 Dropouts
7.5 Jitter
7.6 Digital voice compression systems
36 7.7 Overestimation of STI under low background noise conditions
7.8 Frequency response
37 7.9 Echoes
38 Figure 3 – Effect of a single delayed arrival on the MTF (idealised conditions)
39 7.10 Fast amplitude compression and expansion
Figure 4 – Idealised STI (Male speech Spectrum) versus delay and level of secondary arrival
40 7.11 Non-linear distortion
7.12 Hearing impaired listeners
7.13 Impulsive and fluctuating noise
7.14 Conclusion
41 8 Measurement procedures, post-processing of data and applications
8.1 General
8.2 Acoustical input
43 8.3 Acoustical output
8.4 Electrical input
8.5 Electrical output
8.6 Examples of input/output combinations
8.6.1 Acoustical input – Acoustical output
8.6.2 Electrical input – Electrical output (e.g. assessment of wired and wireless) communication systems)
8.6.3 Acoustical input – Electrical output (e.g. assessment of microphones)
44 8.6.4 Electrical input – Acoustical output (e.g. assessment of PA systems)
8.7 Spatial averaging of STI measurements
45 8.8 Post-processing of measured MTF data
8.9 Issues concerning noise
8.9.1 General
46 8.9.2 Measurement of background noise
8.9.3 Fluctuating noise
8.10 Analysis and interpretation of the results
47 8.11 Binaural STI measurements
9 Use of the STI as a design prediction tool
9.1 Overview
48 9.2 Statistical predictions
9.3 Prediction from simulated impulse response
49 Annexes
Annex A (informative)The basis of the STI concept
A.1 Introduction to this annex
A.1.1 Purpose
A.1.2 Modulation transfer function (MTF)
Figure A.1 – Theoretical expression of the MTF
50 A.1.3 STI model
51 A.1.4 STI modulation frequencies
A.2 Calculation of the STI
A.2.1 General equation for STI
Figure A.2 – Measurement system and frequencies for the STI method
52 A.2.2 Gender-specific octave band weighting and redundancy factors
53 A.2.3 Adjustment of the MTF for ambient noise
A.2.4 Adjustment of the MTF for auditory masking and threshold effects
Table A.1 – MTI octave band weighting factors
54 A.3 Calculation of the modulation transfer ratio values
A.3.1 Direct method: Analysis of the STI test signal
55 A.3.2 Indirect method: Determination of the modulation transfer function (MTF)
56 A.4 Auditory effects on the STI
A.4.1 Overview
A.4.2 Level-dependent auditory masking
57 Figure A.3 – Auditory masking of octave band (k – 1) on octave band (k)
58 Figure A.4 – Relationship between STI and speech level for different reverberation times.
Table A.2 – Auditory masking as a function of the octave band level
59 A.4.3 Absolute speech reception threshold
A.5 Generation of the STI test signal (direct method)
A.5.1 Pink noise source signal
A.5.2 Generating octave band carrier signals
Table A.3 – Absolute speech reception threshold level in octave bands
60 A.5.3 Intensity modulation of the carrier signals
A.5.4 Applying the speech spectrum to the STI test signal
A.6 Spectrum of STI test signal
A.6.1 Standardized speech spectrum
A.6.2 Speech-shaped noise
Table A.4 – Octave band levels (dB) relative to the A-weighted speech level
61 Table A.5 – Filter parameters and s-plane polynomials that produce speech-shaped pink noise.
62 Annex B (normative)STIPA method
B.1 Overview
B.2 Test signal
Table B.1 – Modulation frequencies for the STIPA method
64 Annex C (normative)Verification of STI measuring devices
C.1 Specification of the measuring device
C.2 Signals for testing STI implementations
C.3 Testing the dynamic range in the modulation domain
C.3.1 General
C.3.2 Modulation depth testing for STIPA direct method
Table C.1 – Specification of an STI measuring device
65 C.3.3 Modulation depth testing for STI indirect method
66 C.4 Testing of cross-talk between octave-band filters
C.4.1 Flank attenuation slopes
C.4.2 Octave band filter testing – STIPA direct method
67 C.4.3 Performance verification files
68 Annex D (informative)Use of STI measuring devices
D.1 Overview
D.2 STIPA characterises only the speech transmission channel
69 D.3 Examples of test scenarios for STIPA tests
Figure D.1 – Schematic representation of the definition of a speech transmission channel
70 Table D.1 – Scenario 1, PA with “live” announcer
Table D.2 – Scenario 2, PA with pre-recorded announcements
71 Table D.3 – Scenario 3, “live” meetings and conversations
Table D.4 – Scenario 4, lecture
72 D.4 Equipment and resources needed for a STIPA test
D.4.1 Availability of the test signal
D.4.2 A source of the STIPA test signal
D.4.3 A STIPA analyser
D.5 Steps in the overall procedure
73 Annex E (informative)Qualification of the STI and relationships with other speech intelligibility measures
E.1 Relationship between the STI and word/sentence scores
E.2 Relationship between STI and listening difficulty
Figure E.1 – Relationships between some speech intelligibility measures
74 Figure E.2 – Relationship between STI, speech intelligibility scores and listening difficulty ratings [43], [44]
Table E.1 – Categories for listening difficulty
75 Annex F (informative)Nominal qualification bands for STI
Figure F.1 – STI qualification bands
76 Annex G (informative) Examples of STI qualification bands and typical applications
Table G.1 – Examples between STI qualification bands and typical applications
77 Annex H (informative)Non-native listeners
Table H.1 – Adjusted intelligibility qualification tables for non-native listeners
78 Annex I (informative)Effect of age-related hearing loss and hearing impairment on speech intelligibility
Table I.1 – Adjusted intelligibility qualification tables for normal listeners and people over 60 years old with hearing loss
79 Annex J (normative)Setting and adjustment of STI test signal level
J.1 Overview
J.2 The concept of ‘speech level’ and the method of measurement
J.3 Real speech level
80 J.4 Corrected speech level derived from real speech level
J.5 Comparison of dynamic structures of speech and test signals
Table J.1 – Typical speech and test signal dynamics
81 Table J.2 – Comparison of speech and the test signal
82 Annex K (informative)Example test report sheet for STI measurements
Table K.1 – Example test report sheet
83 Table K.2 – Measurement data record sheet
84 Annex L (normative)Prediction of the STI using statistical methods
86 Annex M (informative)Adjustments to STI data to simulate alternative ambient noise spectra and different speech levels
87 Table M.1 – Flow chart of post-processing adjustment steps
92 Table M.2 – Example calculation
96 Annex N (informative)Other methods of determining speech intelligibility
N.1 Overview
N.2 Word tests
N.3 Modified rhyme tests
97 N.4 Speech intelligibility index (SII)
N.5 PESQ
98 Annex O (informative)Alternative direct methods for measuring Full STI
99 Annex P (normative)Information to be provided by manufacturers
P.1 Purpose of this annex
P.2 Form in which the information is to be provided
P.3 Required information
P.4 Declaration
100 Annex Q (informative)Effect of uncertainties of selected parameters on STI uncertainty
Q.1 STI calculation framework
Q.1.1 Overview
Q.1.2 Statistical MTF
Q.1.3 Corrections
101 Q.1.4 Effective SNR
Q.1.5 Modulation transfer index (MTI)
Q.1.6 Speech transmission index (STI)
102 Q.2 The effect of RT uncertainty on STI uncertainty
Q.2.1 General
Q.2.2 Modulation transfer function
Q.2.3 Uncertainty in the STI
104 Q.2.4 Conclusions:
Q.3 The effect of S/N uncertainty on STI uncertainty
Q.3.1 General
Q.3.2 Ideal transfer function
Figure Q.1 – Uncertainty in absolute value of STI vs reverberation time RT with various degrees of uncertainty in RT
105 Q.3.3 Reverberation
106 Q.3.4 Conclusions:
Q.4 The effect of signal level uncertainty on STI uncertainty
Q.4.1 Overview
Q.4.2 Auditory masking
Figure Q.2 – Uncertainty in absolute value of STI vs reverberation time RT with 1 dB uncertainty in SNR at various SNRs
108 Q.4.3 Conclusions
Figure Q.3 – Uncertainty in absolute value of STI versus reverberation time RT with various degrees of masking.
109 Bibliography

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BS EN IEC 60268-16:2020
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