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IEC 60268-16 Edition 4.0 2011-06 INTERNATIONAL STANDARD NORME INTERNATIONALE So

IEC 60268-16 Edition 4.0 2011-06 INTERNATIONAL STANDARD NORME INTERNATIONALE Sound system equipment – Part 16: Objective rating of speech intelligibility by speech transmission index Equipements 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 XB ICS 33.160.01 PRICE CODE CODE PRIX ISBN 978-2-88912-672-9 ® Registered trademark of the International Electrotechnical Commission Marque déposée de la Commission Electrotechnique Internationale ® This is a preview - click here to buy the full publication – 2 – 60268-16  IEC:2011 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 This is a preview - click here to buy the full publication 60268-16  IEC:2011 – 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 ..................................................................................... 48 Annex C (normative) STITEL method ................................................................................... 49 Annex D (informative) RASTI method (obsolete) .................................................................. 50 Annex E (informative) Qualification of the STI and relationships with other speech intelligibility measures........................................................................................................... 52 Annex F (informative) Nominal qualification bands for STI ................................................... 54 Annex G (informative) Examples of STI qualification bands and typical applications ........... 55 Annex H (informative) Non-native listeners .......................................................................... 56 Annex I (informative) Effect of age-related hearing loss and hearing impairment on speech intelligibility............................................................................................................... 57 Annex J (normative) Calibration of STI test signal level ....................................................... 58 Annex K (informative) Example test report sheet for STI measurements .............................. 60 Annex L (normative) Prediction of STI using statistical methods .......................................... 62 Annex M (informative) Adjustments to measured STI and STIPA results for simulation of occupancy noise and different speech levels .................................................................... 64 Annex N (informative) Other methods of determining speech intelligibility ............................ 68 Bibliography .......................................................................................................................... 70 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) ............................................... 36 Figure A.2 – Theoretical expression of the MTF .................................................................... 37 Figure A.3 – Measurement system and frequencies for the STI method ................................ 39 Figure A.4 – Auditory masking of octave band (k – 1) on octave band (k) ............................. 40 Figure D.1 – Illustration of a practical RASTI test signal ....................................................... 51 Figure E.1 – Relationships between some speech intelligibility measures ............................ 52 Figure E.2 – Relationship between STI, speech intelligibility scores and listening difficulty ratings [34], [35] ...................................................................................................... 53 Figure F.1 – STI qualification bands ...................................................................................... 54 This is a preview - click here to buy the full publication – 4 – 60268-16  IEC:2011 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..................................... 41 Table A.2 – Absolute speech reception threshold level in octave bands ................................ 42 Table A.3 – MTI octave band weighting factors ..................................................................... 42 Table A.4 – Octave band levels (dB) relative to the A-weighted speech level ........................ 43 Table B.1 – Modulation frequencies for the STIPA method .................................................... 48 Table C.1 – Modulation frequencies for the STITEL method .................................................. 49 Table D.1 – Modulation frequencies for the RASTI method ................................................... 50 Table E.1 – Categories for listening difficulty ........................................................................ 53 Table G.1 – Examples between STI qualification bands and typical applications ................... 55 Table H.1 – Adjusted intelligibility qualification tables for non-native listeners ....................... 56 Table I.1 – Adjusted intelligibility qualification tables for normal listeners and people over 60 years old with hearing loss ....................................................................................... 57 Table M.1 – Example calculation .......................................................................................... 64 This is a preview - click here to buy the full publication 60268-16  IEC:2011 – 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. 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