Auditory model for the speech audiogramfrom audibility to intelligibility for words

(work in progress)

Johannes Lyzenga1

Koenraad S. Rhebergen2

1 VUmc, Amsterdam

2 AMC, Amsterdam

Introduction

- History:

- Standard model for sentence intelligibility: SII

- Modified model for sentence intelligibility: SIIcmp

- Comparison of SII and SIIcmp for SRTn and SRTq

- Relation Audibility vs. Intelligibility for sentences

- ? Relationship Audibility and Intelligibility for words ?

- Database of speech audiograms: word scores

- Audibility from modified model for words in quiet

- Relationship Audibility and Intelligibility for words

- Discussion

Speech Intelligibility Index: SII

Assumptions:

- Speech dynamic range of 30 dB, RMS in the middle

- Intensity Importance Function: linear from –15 to +15 dB

RMS

30 dB Dynamic range

Frequency

15 dB “Effective” speech peaks

Level

- SNR calculations executed in frequency bands

- Only the proportion of speech (orange) above the

noise and absolute threshold contributes to the SII

- So: it is basically an Audibility measure!

Calculation of the SII

Frequency

Lev

el (

dB

) 30 dB

Absolute threshold Noise level

Audible speech (orange)

Novel SI model with compression

Introducing compression in the SI model:

- (1) At normal speech levels (ca 65 dB SPL), hearing

in NH listeners is highly compressive

- (2) At very low levels, and for HI listeners, it is not

The SII was designed for NH at normal speech levels (1)

We introduced compression in the calculations (1),

as function of presentation level and hearing loss (2)

And we tried various speech-dynamic ranges

The compression function

Lev

el (

dB

)

After Oxenham, 1995 (PhD thesis)

Schematic diagram of the model(Rhebergen, Lyzenga, Dreschler & Festen, in press)

SI model with compression

Fixed filter:

free field

to eardrum

Fixed filter:

middle ear

Spectrum to

excitation

pattern

Excitation to

specific loudness

(incl compression)

Compress

excitation

pattern

Compressed

excitation pattern

to SIIcmp

FFT-based

Stimulus

Spectrum

Audibility is calculated from the excitation differences for noise and speech: still an Audibility measure

Standard SII predictions

Data set of factory workers:

- Maintenance

work shop for

aircrafts.

- 323 NH: blue

- 65 NIHL: green

- 14 HI: gray

- SIIs in quiet

decrease with

hearing loss !quiet 35dBA 50dBA 65dBA 80dBA

NH

NIHL

HI

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SII

-∞ 35 50 65 80

Level (dBA)

ANSI S3.5, 1997

-∞∞∞∞ 35 50 65 80

Level (dBA)

SI predictions with compression (1)

quiet 35dBA 50dBA 65dBA 80dBAquiet 35dBA 50dBA 65dBA 80dBA

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

quiet 35dBA 50dBA 65dBA 80dBA

NH

NIHL

HI

Range: 30 dB Range: 35 dB Range: 40 dB0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SIIcm

p

-∞ 35 50 65 80

Level (dBA)

-∞ 35 50 65 80

Level (dBA)

-∞ 35 50 65 80

Level (dBA)

SI predictions with compression (2)

quiet 35dBA 50dBA 65dBA 80dBA

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

quiet 35dBA 50dBA 65dBA 80dBA

NH

NIHL

HI

quiet 35dBA 50dBA 65dBA 80dBA

Range: 45 dB Range: 50 dB Range: 55 dB0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

SIIcm

p

-∞ 35 50 65 80

Level (dBA)

-∞ 35 50 65 80

Level (dBA)

-∞ 35 50 65 80

Level (dBA)

PTA

-10 0 10 20 30 40 50 60 70

SII

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

SRTq spread of the SII and SIIcmp values

PTA

-10 0 10 20 30 40 50 60 70

SII

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

ANSI

SIIcmp 45dB

SII

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Pe

rcen

t S

en

ten

ce C

orr

ect

(%)

0

10

20

30

40

50

60

70

80

90

100

Relationship Audibility and Intelligibility

SRTs: short, meaningful, sentences in stat. noise

45-dB speech dynamic range optimal for SIIcmp

50% sentences correct gives an SII of appr. 0.22

SRT

Relationship Audibility and Intelligibility

First for words?

Why words…

- Few data sets of psychometric functions for sentences

- From sentence audibility to intelligibility: very complex

- Physical cues, syntax, semantics, prosody, grammar, etc

- From word audibility to intelligibility: less complex

- A lot of data available for words as function of level

- Database: years of clinical measurements at the AMC

- Both speech and pure-tone audiograms available

- Diverse population: NH, M-HI, S-HI, and intermediates

Available data set

Speech audiogram: word scores for at least 3 levels

Pure-tone audiogram: normal audiometric frequencies

Data from 4 years of clinical measurements

NH: 1479

- Age range [18 – 80(!)]

- Avg: 51, SD: 15 years

Not used today:

M-HI: 1967

S-HI: 1314

Inter: 128210

210

310

4−80

−70

−60

−50

−40

−30

−20

−10

0

dB

HL

Hz

average audiogram nrml, interm, imprd, sevr

Results for 30-dB speech dynamic range

Intelligibility and Audibility for Presentation Level

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Bosman words clinic: P(c) (bl) and Audibility (rd)

Level (dB SPL)

P(c

) &

Au

dib

ility

Intelligibility vs. Audibility: 30-dB dyn.

50% Intelligibility for Audibility of approximately 0.65

0 0.2 0.4 0.6 0.8 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Bosman words clinic: intelligibility

Audibility

P(c

)

Results for 45-dB speech dynamic range

Intelligibility and Audibility for Presentation Level

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Bosman words clinic: P(c) (bl) and Audibility (rd)

Level (dB SPL)

P(c

) &

Au

dib

ility

Intelligibility vs. Audibility: 45-dB dyn.

50% Intelligibility for Audibility of approximately 0.35

0 0.2 0.4 0.6 0.8 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Bosman words clinic: intelligibility

Audibility

P(c

)

Bosman: Intelligibility vs. Audibility in NH

Dyn Range Intelligibility Audibility

30 dB 50% ~0.65

45 dB 50% ~0.35

Sentences 50% ~0.23

Thesis Bosman for NH listeners:

Stimuli Intelligibility Level

Sentences 50% ~20.5

Words 50% ~27.5

Bosman: Word Level for 50% correct is a bit higher ����

Word Audibility needs to be a bit higher: 45 dB Dyn. R.

Discussion

Relationship Audibility and Intelligibility for words:

- Model: plausible relationships for 45-dB speech dyn. range

- The data set shows somewhat different relations than the

data from the thesis of A. Bosman (not shown):

- Refinements needed:

- Separate age groups for NH

- Speech dynamic ranges

- Look at relationship: Sentence Audibility and Intelligibility

Future:

- Maybe we can unearth Intensity Importance functions

- Aim: predict word scores from the audiogram: clinic

Fin

End

Ende

Einde