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DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer

DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer The HEARing CRC & The National Acoustic Laboratories. creating sound value TM. www.hearingcrc.org. Make speech intelligible Make loudness comfortable. Prescribe hearing aids to:.

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DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer

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  1. DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer The HEARing CRC & The National Acoustic Laboratories creatingsoundvalueTM www.hearingcrc.org

  2. Make speech intelligible Make loudness comfortable Prescribe hearing aids to: • Prescription affected by other things • localization, • tonal quality, • detection of environmental sounds, • naturalness.

  3. Loudness model Normal loudness Gain-frequency response Compare Intelligibility achieved Loudness (hearing impaired) Intelligibility model Loudness model Amplified speech spectrum Audiogram Deriving optimal gains - step 1 Speech spectrum & level

  4. The audiograms Rejection criterion : • -30<= G <=60 , where G is the slope • sum(H(f))/3 <=100 , where f is in the set {0.5, 1, 2} kHz Inverted hearing loss profiles used

  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 - step 1 200 audiograms x 6 speech levels  1200 gain–frequency responses, each at 20 frequencies from 125 Hz to 10 kHz

  6. Adjust Final formula Compare Overall prescription approach Psychoacoustics Theoretical predictions Assumptions, rationale Speech science Empirical observations

  7. Limiting compression ratio

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

  9. Loudness model Speech spectrum & level Normal loudness Gain-frequency response Compare Intelligibility achieved Loudness (hearing impaired) Intelligibility model Loudness model Amplified speech spectrum Audiogram The two key ingredients

  10. Psychoacoustics

  11. Frequency selectivity Temporal resolution Central auditory processing Other Why are hearing thresholds so useful? Speech Perception proficiency Hearing thresholds Age Cognitive ability

  12. BKB, VCV and CUNY

  13. Factors affecting prescription

  14. Gain; adults, medium input level(N = 187)

  15. Gain for adults: low & high input levels Suggest that the compression ratio should be slightly higher, at least for clients with mild and moderate hearing loss

  16. Binaural loudness correction

  17. Children Adults Empirical evidence: variations from NAL-NL1 Output level NAL-NL1 Input level

  18. Adults – congenital or acquired?

  19. 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 Effect of language

  20. Tonal versus non-tonal language

  21. 125 250 500 1k 2k 4k 8k 0 20 40 60 80 100 120 Example audiogram: moderate sloping Frequency (Hz) 50 dB 65 dB Hearing threshold (dB HL) 80 dB

  22. 125 250 500 1k 2k 4k 8k 0 20 40 60 80 100 120 Example audiogram: flat 60 Frequency (Hz) 50 dB 65 dB Hearing threshold (dB HL) 80 dB

  23. 125 250 500 1k 2k 4k 8k 0 20 40 60 80 100 120 Example audiogram: steeply sloping Frequency (Hz) 50 dB 65 dB Hearing threshold (dB HL) 80 dB

  24. 125 250 500 1k 2k 4k 8k 0 20 40 60 80 100 120 Example audiogram: extreme ski-slope Frequency (Hz) 50 dB 65 dB Hearing threshold (dB HL) 80 dB

  25. 125 250 500 1k 2k 4k 8k 0 20 40 60 80 100 120 Example audiogram: reverse sloping Frequency (Hz) 50 dB 65 dB Hearing threshold (dB HL) 80 dB

  26. Variables in NAL-NL2 Age Vent Tube Comp speed WBCT N Language Depth Gender RECD Bi-uni CR RECD BWC Experience REUG Aid type UCT I/O REDD MLE REIG REAG Transducer AC CG AC' ABG ESG BC' RESR ESCD BC SSPL2cc Blue = User i/p Grey = internal variable Red = effect of saturation Dash-dot = alternatives Green = stored data SSPLES Limiting type

  27. “A challenge for the profession is to devise fitting procedures that are scientifically defensible and the challenge for the individual audiologist is to choose the best procedures from whatever are available” Denis Byrne, 1998

  28. creatingsoundvalueTM Thanks for listening Acknowledgements 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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