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.<\/p>\n
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| 2<\/td>\n | undefined <\/td>\n<\/tr>\n | ||||||
| 5<\/td>\n | Annex ZA(normative)Normative references to international publicationswith their corresponding European publications <\/td>\n<\/tr>\n | ||||||
| 7<\/td>\n | English CONTENTS <\/td>\n<\/tr>\n | ||||||
| 12<\/td>\n | FOREWORD <\/td>\n<\/tr>\n | ||||||
| 14<\/td>\n | INTRODUCTION <\/td>\n<\/tr>\n | ||||||
| 15<\/td>\n | Tables Table 1 \u2013 How to use this document <\/td>\n<\/tr>\n | ||||||
| 17<\/td>\n | 1 Scope 2 Normative references 3 Terms and definitions <\/td>\n<\/tr>\n | ||||||
| 23<\/td>\n | 4 Description of the STI model 4.1 Overview <\/td>\n<\/tr>\n | ||||||
| 24<\/td>\n | 4.2 Applicability of the STI model 4.3 Theoretical details 4.3.1 Envelope function and envelope spectrum <\/td>\n<\/tr>\n | ||||||
| 25<\/td>\n | 4.3.2 Reduction of modulation 4.3.3 Role of the octave-band noise carriers 4.3.4 Theoretical overview Figures Figure 1 \u2013 Envelope function (panel A) of a 10 s speech signal for the 250 Hz octave band and corresponding envelope spectrum (panel B) <\/td>\n<\/tr>\n | ||||||
| 26<\/td>\n | Figure 2 \u2013 Modulation transfer function \u2013 Input\/output comparison <\/td>\n<\/tr>\n | ||||||
| 27<\/td>\n | 4.4 Measurement of STI 4.4.1 Direct and indirect methods Table 2 \u2013 Comparison of direct and indirect methods <\/td>\n<\/tr>\n | ||||||
| 28<\/td>\n | 4.4.2 Full STI 4.4.3 STIPA 4.4.4 Choice of method <\/td>\n<\/tr>\n | ||||||
| 29<\/td>\n | Table 3 \u2013 Suitability of STI test methods for different types of distortion Table 4 \u2013 Test-method suitability <\/td>\n<\/tr>\n | ||||||
| 30<\/td>\n | 5 Direct method of measuring STI \u2013 User guidance 5.1 Overview Table 5 \u2013 Measurement applications <\/td>\n<\/tr>\n | ||||||
| 31<\/td>\n | 5.2 STIPA 5.3 Application 5.4 Limitations <\/td>\n<\/tr>\n | ||||||
| 32<\/td>\n | 6 Indirect method of measuring STI (impulse response) \u2013 User guidance 6.1 Overview 6.2 Application <\/td>\n<\/tr>\n | ||||||
| 33<\/td>\n | 6.3 Limitations (non-linear distortion) <\/td>\n<\/tr>\n | ||||||
| 34<\/td>\n | 7 Limitations of the STI model 7.1 General <\/td>\n<\/tr>\n | ||||||
| 35<\/td>\n | 7.2 Frequency shifts 7.3 Centre clipping 7.4 Dropouts 7.5 Jitter 7.6 Digital voice compression systems <\/td>\n<\/tr>\n | ||||||
| 36<\/td>\n | 7.7 Overestimation of STI under low background noise conditions 7.8 Frequency response <\/td>\n<\/tr>\n | ||||||
| 37<\/td>\n | 7.9 Echoes <\/td>\n<\/tr>\n | ||||||
| 38<\/td>\n | Figure 3 \u2013 Effect of a single delayed arrival on the MTF (idealised conditions) <\/td>\n<\/tr>\n | ||||||
| 39<\/td>\n | 7.10 Fast amplitude compression and expansion Figure 4 \u2013 Idealised STI (Male speech Spectrum) versus delay and level of secondary arrival <\/td>\n<\/tr>\n | ||||||
| 40<\/td>\n | 7.11 Non-linear distortion 7.12 Hearing impaired listeners 7.13 Impulsive and fluctuating noise 7.14 Conclusion <\/td>\n<\/tr>\n | ||||||
| 41<\/td>\n | 8 Measurement procedures, post-processing of data and applications 8.1 General 8.2 Acoustical input <\/td>\n<\/tr>\n | ||||||
| 43<\/td>\n | 8.3 Acoustical output 8.4 Electrical input 8.5 Electrical output 8.6 Examples of input\/output combinations 8.6.1 Acoustical input \u2013 Acoustical output 8.6.2 Electrical input \u2013 Electrical output (e.g. assessment of wired and wireless) communication systems) 8.6.3 Acoustical input \u2013 Electrical output (e.g. assessment of microphones) <\/td>\n<\/tr>\n | ||||||
| 44<\/td>\n | 8.6.4 Electrical input \u2013 Acoustical output (e.g. assessment of PA systems) 8.7 Spatial averaging of STI measurements <\/td>\n<\/tr>\n | ||||||
| 45<\/td>\n | 8.8 Post-processing of measured MTF data 8.9 Issues concerning noise 8.9.1 General <\/td>\n<\/tr>\n | ||||||
| 46<\/td>\n | 8.9.2 Measurement of background noise 8.9.3 Fluctuating noise 8.10 Analysis and interpretation of the results <\/td>\n<\/tr>\n | ||||||
| 47<\/td>\n | 8.11 Binaural STI measurements 9 Use of the STI as a design prediction tool 9.1 Overview <\/td>\n<\/tr>\n | ||||||
| 48<\/td>\n | 9.2 Statistical predictions 9.3 Prediction from simulated impulse response <\/td>\n<\/tr>\n | ||||||
| 49<\/td>\n | 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 \u2013 Theoretical expression of the MTF <\/td>\n<\/tr>\n | ||||||
| 50<\/td>\n | A.1.3 STI model <\/td>\n<\/tr>\n | ||||||
| 51<\/td>\n | A.1.4 STI modulation frequencies A.2 Calculation of the STI A.2.1 General equation for STI Figure A.2 \u2013 Measurement system and frequencies for the STI method <\/td>\n<\/tr>\n | ||||||
| 52<\/td>\n | A.2.2 Gender-specific octave band weighting and redundancy factors <\/td>\n<\/tr>\n | ||||||
| 53<\/td>\n | 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 \u2013 MTI octave band weighting factors <\/td>\n<\/tr>\n | ||||||
| 54<\/td>\n | A.3 Calculation of the modulation transfer ratio values A.3.1 Direct method: Analysis of the STI test signal <\/td>\n<\/tr>\n | ||||||
| 55<\/td>\n | A.3.2 Indirect method: Determination of the modulation transfer function (MTF) <\/td>\n<\/tr>\n | ||||||
| 56<\/td>\n | A.4 Auditory effects on the STI A.4.1 Overview A.4.2 Level-dependent auditory masking <\/td>\n<\/tr>\n | ||||||
| 57<\/td>\n | Figure A.3 \u2013 Auditory masking of octave band (k \u2013 1) on octave band (k) <\/td>\n<\/tr>\n | ||||||
| 58<\/td>\n | Figure A.4 \u2013 Relationship between STI and speech level for different reverberation times. Table A.2 \u2013 Auditory masking as a function of the octave band level <\/td>\n<\/tr>\n | ||||||
| 59<\/td>\n | 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 \u2013 Absolute speech reception threshold level in octave bands <\/td>\n<\/tr>\n | ||||||
| 60<\/td>\n | 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 \u2013 Octave band levels (dB) relative to the A-weighted speech level <\/td>\n<\/tr>\n | ||||||
| 61<\/td>\n | Table A.5 \u2013 Filter parameters and s-plane polynomials that produce speech-shaped pink noise. <\/td>\n<\/tr>\n | ||||||
| 62<\/td>\n | Annex B (normative)STIPA method B.1 Overview B.2 Test signal Table B.1 \u2013 Modulation frequencies for the STIPA method <\/td>\n<\/tr>\n | ||||||
| 64<\/td>\n | 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 \u2013 Specification of an STI measuring device <\/td>\n<\/tr>\n | ||||||
| 65<\/td>\n | C.3.3 Modulation depth testing for STI indirect method <\/td>\n<\/tr>\n | ||||||
| 66<\/td>\n | C.4 Testing of cross-talk between octave-band filters C.4.1 Flank attenuation slopes C.4.2 Octave band filter testing \u2013 STIPA direct method <\/td>\n<\/tr>\n | ||||||
| 67<\/td>\n | C.4.3 Performance verification files <\/td>\n<\/tr>\n | ||||||
| 68<\/td>\n | Annex D (informative)Use of STI measuring devices D.1 Overview D.2 STIPA characterises only the speech transmission channel <\/td>\n<\/tr>\n | ||||||
| 69<\/td>\n | D.3 Examples of test scenarios for STIPA tests Figure D.1 \u2013 Schematic representation of the definition of a speech transmission channel <\/td>\n<\/tr>\n | ||||||
| 70<\/td>\n | Table D.1 \u2013 Scenario 1, PA with “live” announcer Table D.2 \u2013 Scenario 2, PA with pre-recorded announcements <\/td>\n<\/tr>\n | ||||||
| 71<\/td>\n | Table D.3 \u2013 Scenario 3, “live” meetings and conversations Table D.4 \u2013 Scenario 4, lecture <\/td>\n<\/tr>\n | ||||||
| 72<\/td>\n | 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 <\/td>\n<\/tr>\n | ||||||
| 73<\/td>\n | 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 \u2013 Relationships between some speech intelligibility measures <\/td>\n<\/tr>\n | ||||||
| 74<\/td>\n | Figure E.2 \u2013 Relationship between STI, speech intelligibility scores and listening difficulty ratings [43], [44] Table E.1 \u2013 Categories for listening difficulty <\/td>\n<\/tr>\n | ||||||
| 75<\/td>\n | Annex F (informative)Nominal qualification bands for STI Figure F.1 \u2013 STI qualification bands <\/td>\n<\/tr>\n | ||||||
| 76<\/td>\n | Annex G (informative) Examples of STI qualification bands and typical applications Table G.1 \u2013 Examples between STI qualification bands and typical applications <\/td>\n<\/tr>\n | ||||||
| 77<\/td>\n | Annex H (informative)Non-native listeners Table H.1 \u2013 Adjusted intelligibility qualification tables for non-native listeners <\/td>\n<\/tr>\n | ||||||
| 78<\/td>\n | Annex I (informative)Effect of age-related hearing loss and hearing impairment on speech intelligibility Table I.1 \u2013 Adjusted intelligibility qualification tables for normal listeners and people over 60 years old with hearing loss <\/td>\n<\/tr>\n | ||||||
| 79<\/td>\n | 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 <\/td>\n<\/tr>\n | ||||||
| 80<\/td>\n | J.4 Corrected speech level derived from real speech level J.5 Comparison of dynamic structures of speech and test signals Table J.1 \u2013 Typical speech and test signal dynamics <\/td>\n<\/tr>\n | ||||||
| 81<\/td>\n | Table J.2 \u2013 Comparison of speech and the test signal <\/td>\n<\/tr>\n | ||||||
| 82<\/td>\n | Annex K (informative)Example test report sheet for STI measurements Table K.1 \u2013 Example test report sheet <\/td>\n<\/tr>\n | ||||||
| 83<\/td>\n | Table K.2 \u2013 Measurement data record sheet <\/td>\n<\/tr>\n | ||||||
| 84<\/td>\n | Annex L (normative)Prediction of the STI using statistical methods <\/td>\n<\/tr>\n | ||||||
| 86<\/td>\n | Annex M (informative)Adjustments to STI data to simulate alternative ambient noise spectra and different speech levels <\/td>\n<\/tr>\n | ||||||
| 87<\/td>\n | Table M.1 \u2013 Flow chart of post-processing adjustment steps <\/td>\n<\/tr>\n | ||||||
| 92<\/td>\n | Table M.2 \u2013 Example calculation <\/td>\n<\/tr>\n | ||||||
| 96<\/td>\n | Annex N (informative)Other methods of determining speech intelligibility N.1 Overview N.2 Word tests N.3 Modified rhyme tests <\/td>\n<\/tr>\n | ||||||
| 97<\/td>\n | N.4 Speech intelligibility index (SII) N.5 PESQ <\/td>\n<\/tr>\n | ||||||
| 98<\/td>\n | Annex O (informative)Alternative direct methods for measuring Full STI <\/td>\n<\/tr>\n | ||||||
| 99<\/td>\n | 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 <\/td>\n<\/tr>\n | ||||||
| 100<\/td>\n | 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 <\/td>\n<\/tr>\n | ||||||
| 101<\/td>\n | Q.1.4 Effective SNR Q.1.5 Modulation transfer index (MTI) Q.1.6 Speech transmission index (STI) <\/td>\n<\/tr>\n | ||||||
| 102<\/td>\n | 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 <\/td>\n<\/tr>\n | ||||||
| 104<\/td>\n | 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 \u2013 Uncertainty in absolute value of STI vs reverberation time RT with various degrees of uncertainty in RT <\/td>\n<\/tr>\n | ||||||
| 105<\/td>\n | Q.3.3 Reverberation <\/td>\n<\/tr>\n | ||||||
| 106<\/td>\n | 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 \u2013 Uncertainty in absolute value of STI vs reverberation time RT with 1 dB uncertainty in SNR at various SNRs <\/td>\n<\/tr>\n | ||||||
| 108<\/td>\n | Q.4.3 Conclusions Figure Q.3 \u2013 Uncertainty in absolute value of STI versus reverberation time RT with various degrees of masking. <\/td>\n<\/tr>\n | ||||||
| 109<\/td>\n | Bibliography <\/td>\n<\/tr>\n<\/table>\n","protected":false},"excerpt":{"rendered":" Sound system equipment – Objective rating of speech intelligibility by speech transmission index<\/b><\/p>\n |