creating sound valueTM

The NAL-NL2 prescription procedureGitte Keidser, Harvey Dillon, Teresa Ching, Matthew Flax, Scott Brewer

National Acoustic Laboratories and the HEARing CRCAdult Hearing Screening, June 2010, Lake Como

www.hearingcrc.org creating sound valueTM

creating sound valueTM

NAL-NL1

Empirical observations

Overall approach to prescription

Theoretical predictions

Psychoacoustics

Speech science

Assumptions, rationale NAL-NL2

Compare

Adjust

creating sound valueTM

• Make speech intelligible• Make loudness comfortable

Prescription affected by other things – localization, – tonal quality, – detection of environmental sounds, – naturalness

Rationale

creating sound valueTM

Compare

Speech spectrum & level

Gain-frequency response

Amplified speech spectrum

Loudness model

Normal loudness

Loudness model

Loudness (hearing impaired)

Audiogram

Intelligibility model

Intelligibility achieved

Deriving optimal gains

creating sound valueTM

Audiogram 1 Speech level 1 Optimal gain frequency response

Audiogram 1 Speech level 2 Optimal gain frequency response

Audiogram 1 Speech level 3 Optimal gain frequency response

Audiogram 2 Speech level 1 Optimal gain frequency response

200 audiograms x 6 speech levels 1200 gain–frequency responses, each at 20 frequencies from 125 Hz to 10 kHz

24,000 data points

Deriving optimal gains

creating sound valueTM

A neural networkH250 H500 H1000 H2000 H8k SPL

G250 G500 G1000 G2000 G8k

Multi-dimensional equation

creating sound valueTM

Compare

Speech spectrum & level

Gain-frequency response

Amplified speech spectrum

Loudness model

Normal loudness

Loudness model

Loudness (hearing impaired)

Audiogram

Intelligibility model

Intelligibility achieved

Deriving optimal gains

New

creating sound valueTM

30 Sensation level (dB)

1

m

p

SIISIIansi = Ai.Ii.Li

SII = Aeff.Ii.Li

1: Change to SII model

creating sound valueTM

1: Change to SII model

• Speech recognition data collected on 75 adults with varied degree of hearing loss– new effective audibility

factor in SII model– Different gain-

frequency response shape

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45NL1 (50 dB)NL1 (65 dB)NL1 (80 dB)

Frequency in Hz

Inse

rtion

gai

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creating sound valueTM

Gain; 187 adults, medium input level

2: Desired gain

creating sound valueTM

Input level

Output level

AdultsChildren

NAL-NL1

2: Desired gain

Gain; adults vs children

creating sound valueTM

2: Desired gain

Limiting compression for severe/profound hearing loss(Fast compression)

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Fast-acting compressionSlow-acting compression

Frequency in Hz

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gai

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creating sound valueTM

• Gain at each frequency depends on importance of each frequency

• Low frequencies more important in tonal languages

• Two versions of NAL-NL2– Tonal languages– Non-tonal languages

3: Effect of language

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Non-tonal language

Tonal language

Frequency in Hz

Inse

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creating sound valueTM

• New features in NAL-NL2– Different gain-frequency response shape and

higher compression ratios– Different compression ratios for fast and slow

compressors (severe/profound hearing loss)– Gender dependent gain– Age dependent gain– Language dependent gain (tonal vs non-tonal)– Gain adaptation for new hearing aid users

Summary

creating sound valueTM creating sound valueTM

This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program

Thanks for listening

www.hearingcrc.org www.nal.gov.au

Acknowledgements

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