standardization of the speech transmission index

Acousteen Herman J.M. Steeneken

Standardization of theSpeech 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

• Conclusions


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)


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)


Criteria for Speech Communication Quality

Measures:Speech IntelligibilityVocal 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 areasfair normal Personal comm. systems fair normal


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)


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


Qualification and relation between subjective measures and STI


Common Intelligibility Scale, CISBarnett 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


Relation STI versus SII

0

0,2

0,4

0,6

0,8

1

0 0,2 0,4 0,6 0,8 1

STI

SII

r = 0.93


Relation SIL versus STI/SII

0

0,2

0,4

0,6

0,8

1

-10 -5 0 5 10 15 20 25 30 35

LSA-LLN

STI

/ S

II

STI

SII

r = 0.97 (STI)r = 0.95 (SII)


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


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)


Calibration (Proposed)

• Reference speech signals at well definedconditions (through internet)

• Standardized spread sheets to calculate objective measures

• Specific software to process digital speech

samples for listening tests


Conclusions

• Increasing interest in verbal warning systems

• Revised standards on “ergonomic assessmentof speech communication”, alarm and warning

systems, all STI methods

• To be used by decision makers and designers

• Criteria, Assessment methods, and Predictionmethods included

standardization of the speech transmission index

Documents