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Standardization of the Speech Transmission Index

Standardization of the Speech Transmission Index. Herman J.M. Steeneken Former convenor: ISO TC159/SC5/WG3, CEN TC 122/WG8. Overview. Workgroup Activities Scope and Field of Application of “ISO-9921” Criteria for Speech Communication Quality Assessment Methods Prediction methods

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Standardization of the Speech Transmission Index

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  1. Standardization of theSpeech Transmission Index Herman J.M. Steeneken Former convenor: ISO TC159/SC5/WG3, CEN TC 122/WG8

  2. Overview • Workgroup Activities • Scope and Field of Application of “ISO-9921” • Criteria for Speech Communication Quality • Assessment Methods • Prediction methods • Conclusions

  3. Workgroup activities (ISO, IEC) • Standardisation of acoustical warning signals, (review ISO-7731, FDIS 2002, CEN standard next) • Standardisation of Speech Transmission Quality, (review ISO-9921, FDIS 2002, CEN standard next) • Standardisation of Speech Transmission Index, (review IEC-60268-16, CDV 2002) • Standardisation of Sound systems for emergency purposes (review IEC 60849, CDV 2002)

  4. Scope and Field of Applications of ISO-9921 Criteria for speech communication quality - to be understood by designers and responsible people - sub-divided into representative groups of applications Assessment methods (simple and advanced) Prediction methods (related to assessment)

  5. Criteria for Speech Communication Quality Measures: Speech Intelligibility Vocal effort of speaker Applications: Alert and warning poor loud Person-to-person (critical) fair loud Person-to-person (relaxed) good normal Public address in public areas fair normal Personal comm. systems fair normal

  6. Assessment Methods Subjective Assessment • Mean Opinion Scores simple • Sentence Intelligibility simple • (embedded) Word lists advanced Objective Assessment • Speech Interference Level (SIL) simple • Speech Transmission Index (STI) advanced • Speech Intelligibility Index (SII)

  7. Relation between subj. and obj. intelligibility measures Qualif. Sent. % CVC % PB % STI LSA – LLN SII nonsense meaning dB Excellent 100 >81 > 98 >0.75 >21 >0.75 Good 100 70-81 93-98 0.60-0.75 15 - 21 Fair 100 53-70 80-93 0.45-0.60 10 - 15 Poor 70-100 31-53 60-80 0.30-0.45 3 - 10 <0.45 Bad <70 <31 <60 < 0.30 < 3

  8. Qualification and relation between subjective measures and STI

  9. Common Intelligibility Scale, CIS Barnett and Knight, IOA 1994 CIS not linear with SNR  = STI  = 100 - ALcons x = AI  = PB words (256 words)  = Short Sentences  = PB words (1000 words)  = 1000 syllables

  10. Relation STI versus SII r = 0.93

  11. Relation SIL versus STI/SII r = 0.97 (STI) r = 0.95 (SII)

  12. Criteria in ISO-9921and IEC 60849 Application Intell. SIL STI (CIS) Vocal dB effort Alert and warning (simple) poor 8 0.40 0.6 Loud Alert and warning (critical) fair 11 0.50 0.7 Loud Person-to-person (critical) fair 11 0.50 0.7 Loud Person-to-person (relaxed) good 15 0.60 0.8 Normal Public address in public areas fair 11 0.50 0.7 Normal Personal communication fair 11 0.50 0.7 Normal

  13. Prediction Methods SIL, vocal effort, noise (ISO-9921) STI, vocal effort, gender speaker,noise, band-pass limiting, masking, reverberation, echoes, non-linearity, (IEC 60268-16) SII, vocal effort, noise, band-pass limiting, masking, (ANSI 3 5.2)

  14. Calibration (Proposed) • Reference speech signals at well defined conditions (through internet) • Standardized spread sheets to calculate objective measures • Specific software to process digital speech samples for listening tests

  15. Conclusions • Increasing interest in verbal warning systems • Revised standards on “ergonomic assessment of speech communication”, alarm and warning systems, all STI methods • To be used by decision makers and designers • Criteria, Assessment methods, and Prediction methods included

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