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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
020406080
100
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
-15-10
-50
0 5 10 15
Band number
Diff
eren
ce re
lativ
e to
sin
e (d
B)
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)
-15
-10
-5
0
5
10
15
20
100 1000 10000
Frequency (Hz)
Des
ired
extr
a ga
in (d
B)
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.
-15
-10
-5
0
5
10
15
20
100 1000 10000
Frequency (Hz)
Des
ired
extr
a ga
in (d
B)
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
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100 120
Hearing loss (dB HL)
Extr
a ga
in (d
B)
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
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100 120
Hearing loss (dB HL)
Extr
a ga
in (d
B)
G(80)G(50)Linear (G(50))Linear (G(80))
0
10
20
30
40
50
60
70
80
90
100
100 1000 10000
0
5
10
15
20
25
30
35
40
100 1000 10000
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.