Audiogram+:GN Resound proprietary fitting rule

Ole Dyrlund

GN ReSound Audiological Research Copenhagen

Loudness normalization - Principle

Background for Audiogram+

! Audiogram+ is a loudness normalization rule adapted to the 14 band compression system in Canta based on clinical trials. � Allen J.B., Hall J.L., Jeng P.S. (1990)

! Audiogram+ calculates gain targets at the 11 audiometric frequencies for 50 and 80 dB SPL inputs based on air conduction thresholds and a number of additional factors.

! Gain targets provide an optimal trade-off between speech perception and listening comfort

Speech perception with Audiogram+

Speech-in-Noise Test Results

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CIC (n=18) ITE/BTE (n=33) PBTE (n=21)

Model

Perc

ent

Cor

rect

UnaidedOwnCanta-P1Canta-P2

�Own� aids are a selection of digital and programmable instruments

14 Band Compression system

Effect of input signal for 14 band system

Broadband vs. sine input for same overall level

-25-20

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Band number

Diff

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ce re

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sin

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White noise vs. sineinputSpeech shaped vs. Sine input

At 1kHz broadband input is 9 dB lower than sine input

Broad band vs. sine band input

Insertion gain dB

Frequency

50 dB Input80 dB Input

Broad band InputSine Input

Audiogram+: Additional factors taken into account

! Severe Hearing Losses! Ski-slope Hearing losses! First Time Users! Air-Bone Gap! UCL! Age! Previous type of amplification

Accuracy of Audiogram+

�Very accurate prediction of average desiredamplification for mild, moderate and severelosses

�Standard deviation twice as high for severehearing losses, meaning more fine-tuning isneeded for these losses.

Prescribed versus fine-tuned gain (mild to moderate HL)

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Frequency (Hz)

Des

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extr

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Mean differences and standard deviation (SD) between Audiogram+ prescribed gain targets and the final gain setting preferred by test subjects. Blue line: 80 dB inputs, blue dotted line: corresponding Standard Deviation. Black line: 50 dB inputs, black dotted line: corresponding Standard Deviation.

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Frequency (Hz)

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Prescribed versus fine-tuned gain (severe HL)

Mean differences and standard deviation (SD) between Audiogram+ prescribed gain targets and the final gain setting preferred by test subjects. Blue line: 80 dB inputs, blue dotted line: corresponding Standard Deviation. Black line: 50 dB inputs, black dotted line: corresponding Standard Deviation.

Can prescription accuracy be increased for severe and profound losses?

Design

! Fitting data from several test sites were divided in two groups according to previous use of linear amplification or fast acting WDRC

! Target prescriptions calculated by the original Audiogram+ algorithm were compared with the gain preferred by the users

! Comparison was carried out at 0.25, 0.5, 1, 2, 4 and 6 kHz.

Test subjects

! 59 users of fast acting WRDC! 36 users of linear hearing aids! All users binaurally fitted! All experienced users of hearing aids

Previous nonlinear users, 0.5 kHz

y = 0.0749x - 0.1417

y = 0.0932x - 1.4607

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Hearing loss (dB HL)

Extr

a ga

in (d

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G(80)G(50)Linear (G(50))Linear (G(80))

Previous linear users, 0.5 kHz

y = 0.2034x - 4.2815

y = 0.2929x - 7.5298

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Hearing loss (dB HL)

Extr

a ga

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G(80)G(50)Linear (G(50))Linear (G(80))

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T80 (Lin)T50 (Lin)T80 (Nonlin)T50 (Nonlin)

New rule: Example

Accuracy of improved fitting rule

G(80) G(50)HTL 250 500 1 2 4 6 All 250 500 1 2 4 6 All

Linear <65 Diff. -1 -2 -1 0 1 1 -1 -1 -1 -1 0 1 2 -1SD 6 3 4 4 5 3 4 4 4 4 4 5 6 5

>65 Diff. 1 2 0 -1 0 0 0 1 1 -2 -2 -1 -2 -1SD 11 9 7 8 9 9 9 11 6 4 5 6 7 6

Nonlinear <65 Diff. 0 0 0 0 1 0 0 1 0 0 0 0 -1 0SD 4 4 4 5 4 3 4 4 4 4 5 4 4 4

>65 Diff. 2 1 0 0 1 0 0 -1 1 -1 0 0 -1 0SD 7 6 6 6 6 6 6 7 7 5 6 6 6 6

Previous <65 Diff. -1 0 0 0 -2 -2 -1 -1 0 1 1 -1 -1 0combined SD 4 4 4 5 5 4 4 5 4 4 4 5 5 4rue >65 Diff. 1 0 1 2 4 4 2 0 0 0 0 1 2 1

SD 11 9 8 10 10 10 10 9 8 5 7 9 9 8

Mean difference and SD between preferred fitting and prescription:

Accuracy of improved fitting rule

0123456789

10

SD dB

80 dB Input 50 dB Input

>65 Linear >65 Non-Linear >65 Combined <65 All

Conclusion

! Audiogram+ is tailored to the Resound compression system (channels, time constants)

! Audiogram+ gives an optimal trade-off between speech perception and listening comfort and a high prescription accuracy.

! Tested in a large number of clinical trials ! For severe hearing losses use of separate

prescriptions for previous users of linear and nonlinear amplification improves the prescription accuracy.