Auditory model for the speech audiogram from audibility to intelligibility for words (work in progress)

Transcription

1 Auditory model for the speech audiogram from audibility to intelligibility for words (work in progress) Johannes Lyzenga 1 Koenraad S. Rhebergen 2 1 VUmc, Amsterdam 2 AMC, Amsterdam

2 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

3 Speech Intelligibility Index: SII Level 3 db Dynamic range RMS 15 db Effective speech peaks Frequency Assumptions: - Speech dynamic range of 3 db, RMS in the middle - Intensity Importance Function: linear from 15 to +15 db

4 Calculation of the SII Audible speech (orange) Level (db) 3 db Absolute threshold Noise 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! Frequency

5 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

6 The compression function Level (db) After Oxenham, 1995 (PhD thesis)

7 Schematic diagram of the model (Rhebergen, Lyzenga, Dreschler & Festen, in press) SI model with compression Compress excitation pattern Compressed excitation pattern to SIIcmp FFT-based Stimulus Spectrum Fixed filter: free field to eardrum Fixed filter: middle ear Spectrum to excitation pattern Audibility is calculated from the excitation differences for noise and speech: still an Audibility measure Excitation to specific loudness (incl compression)

8 Standard SII predictions Data set of factory workers: - Maintenance work shop for aircrafts NH: blue - 65 NIHL: green - 14 HI: gray SII ANSI S3.5, 1997 NH NIHL HI - SIIs in quiet decrease with hearing loss! quiet 35dBA 5dBA 65dBA 8dBA Level (dba) Level (dba)

9 SI predictions with compression (1).7.6 Range: 3 db Range: 35 db Range: 4 db NH NIHL HI.5 SIIcmp quiet 35dBA 5dBA 65dBA 8dBA Level (dba) quiet 35dBA 5dBA 65dBA 8dBA Level (dba) quiet 35dBA 5dBA 65dBA 8dBA Level (dba)

10 SI predictions with compression (2).7.6 Range: 45 db Range: 5 db Range: 55 db 7 6 NH NIHL HI.5 5 SIIcmp quiet 35dBA 5dBA 65dBA 8dBA Level (dba) quiet 35dBA 5dBA 65dBA 8dBA Level (dba) quiet 35dBA 5dBA 65dBA 8dBA Level (dba)

11 SRTq spread of the SII and SIIcmp values,8,7,6,8,7,6 ANSI SIIcmp 45dB,5,5 SII,4 SII,4,3,3,2,2,1,1, , PTA PTA

12 Relationship Audibility and Intelligibility SRTs: short, meaningful, sentences in stat. noise 1 9 Percent Sentence Correct (%) SRT SII 45-dB speech dynamic range optimal for SIIcmp 5% sentences correct gives an SII of appr..22

13 Relationship Audibility and Intelligibility Why words First for 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

14 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: Age range [18 8(!)] - Avg: 51, SD: 15 years average audiogram nrml, interm, imprd, sevr Not used today: M-HI: 1967 S-HI: 1314 Inter: 1282 db HL Hz

15 Results for 3-dB speech dynamic range 1 Bosman words clinic: P(c) (bl) and Audibility (rd) P(c) & Audibility Level (db SPL) Intelligibility and Audibility for Presentation Level

16 Intelligibility vs. Audibility: 3-dB dyn. 1 Bosman words clinic: intelligibility P(c) Audibility 5% Intelligibility for Audibility of approximately.65

17 Results for 45-dB speech dynamic range 1 Bosman words clinic: P(c) (bl) and Audibility (rd) P(c) & Audibility Level (db SPL) Intelligibility and Audibility for Presentation Level

18 Intelligibility vs. Audibility: 45-dB dyn. 1 Bosman words clinic: intelligibility P(c) Audibility 5% Intelligibility for Audibility of approximately.35

19 Bosman: Intelligibility vs. Audibility in NH Dyn Range Intelligibility Audibility 3 db 5% ~ db 5% ~.35 Sentences 5% ~.23 Thesis Bosman for NH listeners: Stimuli Intelligibility Level Sentences 5% ~2.5 Words 5% ~27.5 Bosman: Word Level for 5% correct is a bit higher Word Audibility needs to be a bit higher: 45 db Dyn. R.

20 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

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