Creating sound value TM DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt...

creating sound valueTM

DEVELOPMENT OF NAL-NL2

Harvey Dillon, Gitte Keidser, Teresa Ching,

Matt Flax, Scott Brewer

The HEARing CRC & The National Acoustic Laboratories

www.hearingcrc.org creating sound valueTM


Prescribe hearing aids to:

• Make speech intelligible

• Make loudness comfortable

• Prescription affected by other things – localization, – tonal quality, – detection of environmental sounds, – naturalness.


Compare

Deriving optimal gains - step 1

Speech spectrum & level

Gain-frequency response

Amplified speech spectrum

Loudness model

Normal loudness

Loudness model

Loudness (hearing impaired)

Audiogram

Intelligibility model

Intelligibility achieved


Inverted hearing loss profiles used

Rejection criterion :-30<= G <=60 , where G is the slopesum(H(f))/3 <=100 , where f is in the set {0.5, 1, 2} kHz

The audiograms


Audiogram 1 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

Deriving optimal gains - step 1


Overall prescription approach

Theoretical predictions

Empirical observations

Psychoacoustics

Speech science

Assumptions, rationale

Final formula

Compare

Adjust


Limiting compression ratio


Multi-dimensional equation

A neural network

H250 H500 H1000 H2000 H8k SPL

G250 G500 G1000 G2000 G8k


The two key ingredients

Compare

Speech spectrum & level

Gain-frequency response

Amplified speech spectrum

Loudness model

Normal loudness

Loudness model

Loudness (hearing impaired)

Audiogram

Intelligibility model

Intelligibility achieved


Psychoacoustics


Why are hearing thresholds so useful?

Hearing thresholds

Speech Perception proficiency

Frequency selectivity

Temporal resolution

Central auditory processing

OtherAge

Cognitive ability


BKB, VCV and CUNY


Factors affecting prescription


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


-2

-1.5

-1

-0.5

0

0.5

1

1.5

Pre

ferr

ed

ga

in d

ev

iati

on

fro

m

NA

L-N

L1

re

ga

in p

refe

rre

d a

t 6

5

dB

SP

L in

dB

50 80

Input level in dB SPL

Smeds et al. 2006 Zakis et al. 2007

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


Binaural loudness correction

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120

Input level (dB)

Ga

in v

ari

ati

on

(d

B)


Empirical evidence: variations from NAL-NL1

Input level

Output level

AdultsChildren

NAL-NL1


Adults – congenital or acquired?

-14

-12

-10

-8

-6

-4

-2

0P

refe

rred

gai

n d

evia

tio

n

fro

m N

AL

-RP

(d

B)

LFA HFA

Congenital(N=15)

Acquired(N=28)


Effect of language

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


0

5

10

15

20

25

30

35

40

100 1000 10000

Frequency in Hz

Inse

rtion

gai

n in

dB

NAL-NL1

Male, exp, non-tonal

Male, exp, tonal

Tonal versus non-tonal language


Example audiogram: moderate sloping

05

10

15202530

3540

100 1000 10000

Frequency (Hz)

Inse

rtio

n G

ain

(dB

)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

He

arin

g t

hre

sho

ld (

dB

HL

) 50 dB

65 dB

80 dB


05

10

15202530

3540

100 1000 10000

Frequency (Hz)

Inse

rtio

n G

ain

(dB

)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

He

arin

g t

hre

sho

ld (

dB

HL

)

50 dB

65 dB

80 dB

Example audiogram: flat 60


05

10

15202530

3540

100 1000 10000

Frequency (Hz)

Inse

rtio

n G

ain

(dB

)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

He

arin

g t

hre

sho

ld (

dB

HL

) 50 dB

65 dB

80 dB

Example audiogram: steeply sloping


0

5

10

15

20

25

30

35

100 1000 10000

Frequency (Hz)

Inse

rtio

n G

ain

(dB

)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

He

arin

g t

hre

sho

ld (

dB

HL

) 50 dB

65 dB

80 dB

Example audiogram: extreme ski-slope


0

5

10

15

20

25

30

100 1000 10000

Frequency (Hz)

Inse

rtio

n G

ain

(dB

)

250125 500 1k 2k 4k 8k

0

20

40

60

80

100

120

Frequency (Hz)

He

arin

g t

hre

sho

ld (

dB

HL

)

50 dB65 dB

80 dB

Example audiogram: reverse sloping


Variables in NAL-NL2

AC

BC'

REDD

ABG

BC

REIG

N

BWC

WBCT

REAG

REUG

Bi-uni Gender

Age

Experience

RESR

CG

RECD

MLE

SSPL2cc

Limiting type

SSPLES

ESCD

Aid type

I/O

Vent Tube

UCT

Blue = User i/p

Grey = internal variable

Red = effect of saturation

Dash-dot = alternatives

Green = stored data

CR

Comp speed

Language

AC'

ESG

DepthRECD

Transducer


“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


Acknowledgements


This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program

Thanks for listening

www.hearingcrc.org

www.nal.gov.au

Creating sound value TM DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt...

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Transcript of Creating sound value TM DEVELOPMENT OF NAL-NL2 Harvey Dillon, Gitte Keidser, Teresa Ching, Matt...