The NAL-NL2 prescription procedure

runmidgeAI and Robotics

Oct 20, 2013 (3 years and 5 months ago)

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creating

sound

value
TM


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


www.hearingcrc.org



creating

sound

value
TM



creating

sound

value
TM


NAL
-
NL1

Empirical

observations

Overall approach to prescription

Theoretical

predictions

Psychoacoustics

Speech science

Assumptions,


rationale

NAL
-
NL2

Compare

Adjust


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sound

value
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Make speech intelligible


Make loudness comfortable




Prescription affected by other things


localization,


tonal quality,


detection of environmental sounds,


naturalness


Rationale


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sound

value
TM


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

value
TM


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

value
TM


A neural network

H
250

H
500

H
1000

H
2000

H
8k

SPL

G
250

G
500

G
1000

G
2000

G
8k

Multi
-
dimensional equation


creating

sound

value
TM


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

value
TM


30

Sensation level (dB)

1

m

p

SII

SII
ansi

=



A
i
.I
i
.L
i

SII

=



A
eff
.I
i
.L
i

1: Change to SII model


creating

sound

value
TM


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

0
5
10
15
20
25
30
35
40
45
100
1000
10000
Insertion gain in dB

Frequency in Hz

NL1 (50 dB)
NL1 (65 dB)
NL1 (80 dB)
NL2 (50 dB)
NL2 (65 dB)
NL2 (80 dB)

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sound

value
TM


Gain;
187 adults,
medium input
level

2: Desired gain


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sound

value
TM



Input level

Output level

Adults

Children

NAL
-
NL1

2: Desired gain

Gain;
adults
vs

children


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sound

value
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2: Desired gain

Limiting compression for severe/profound hearing loss

(Fast compression)

0
10
20
30
40
50
60
100
1000
10000
Insertion gain in dB

Frequency in Hz

Fast-acting compression
Slow-acting compression

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sound

value
TM



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

0
5
10
15
20
25
30
35
100
1000
10000
Insertion gain in dB

Frequency in Hz

Non-tonal language
Tonal language

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sound

value
TM



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

value
TM



creating

sound

value
TM


This research was financially supported by the
HEARing

CRC
established and supported under the Australian Government’s
Cooperative Research
Centres

Program

www.hearingcrc.org

www.nal.gov.au


Acknowledgements

For further information: