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The NAL-NL2 prescription procedure

The NAL-NL2 prescription procedure Gitte Keidser , Harvey Dillon, Teresa Ching , Matthew Flax, Scott Brewer National Acoustic Laboratories and the HEARing CRC Adult Hearing Screening, June 2010, Lake Como. creating sound value TM. www.hearingcrc.org. NAL-NL2.

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The NAL-NL2 prescription procedure

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  1. The NAL-NL2 prescription procedure GitteKeidser, Harvey Dillon, Teresa Ching, Matthew Flax, Scott Brewer National Acoustic Laboratories and the HEARing CRC Adult Hearing Screening, June 2010, Lake Como creatingsoundvalueTM www.hearingcrc.org

  2. NAL-NL2 Overall approach to prescription Psychoacoustics NAL-NL1 Theoretical predictions Adjust Assumptions, rationale Compare Speech science Empirical observations

  3. Make speech intelligible Make loudness comfortable Rationale • Prescription affected by other things • localization, • tonal quality, • detection of environmental sounds, • naturalness

  4. Gain-frequency response Intelligibility achieved Loudness (hearing impaired) Amplified speech spectrum Intelligibility model Loudness model Audiogram Deriving optimal gains Normal loudness Loudness model Speech spectrum & level Compare

  5. Audiogram 1 Audiogram 1 Audiogram 1 Audiogram 2 Speech level 1 Speech level 2 Speech level 3 Speech level 1 Optimal gain frequency response Optimal gain frequency response Optimal gain frequency response Optimal gain frequency response Deriving optimal gains 200 audiograms x 6 speech levels  1200 gain–frequency responses, each at 20 frequencies from 125 Hz to 10 kHz 24,000 data points

  6. A neural network Multi-dimensional equation H250 H500 H1000 H2000 H8k SPL G250 G500 G1000 G2000 G8k

  7. Gain-frequency response Intelligibility achieved Loudness (hearing impaired) Amplified speech spectrum Intelligibility model Loudness model Audiogram Deriving optimal gains New Normal loudness Loudness model Speech spectrum & level Compare

  8. m p 1: Change to SII model SII SIIansi=Ai.Ii.Li 1 SII=Aeff.Ii.Li Sensation level (dB) 30

  9. 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

  10. 2: Desired gain Gain; 187 adults, medium input level

  11. Children Adults 2: Desired gain Gain; adults vs children Output level NAL-NL1 Input level

  12. 2: Desired gain Limiting compression for severe/profound hearing loss(Fast compression)

  13. 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

  14. 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

  15. creatingsoundvalueTM Acknowledgements Thanks for listening For further information: www.hearingcrc.org www.nal.gov.au This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program

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