Will technological advances improve the outcome?

Will technological advances improve the outcome?

Ruth Bentler

University of iowa

What is new?

Choices re feedback control Options re directional microphones Digital noise reduction

Directional microphones

OmnidirectionalOmnidirectional CardioidCardioid

Hypercardioid Hypercardioid Supercardioid Supercardioid

Polar Response PatternFree field characteristics of different types of microphones (Knowles TB 21)

Quick Tutorial

Ways to build directivity into a hearing aid case:• Single mic with two ports

• Two omni mics

• Combination of a & b (DMic, eg)

• Three mics (Siemens Triano)

• Mic array (Etymotic Link-It, e.g.)

Quick tutorial cont

Ways to implement directionality in the hearing aid case:• Fixed polar pattern

• Program different polar patterns in different memories

• Automatic directional mode

• Dynamic/Adaptive directional mode

Adaptive Directionality

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Adaptive Directionality90

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Adaptive Directionality

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In a diffuse field….

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Ricketts & others (1999-02)

Two mics capable of providing same advantage to user as one mic design;

Digital implementation not necessary; Cannot predict who will benefit based on

audiogram; …benefit decreases as reverberation

increases, etc; LF compensation for losses> 40 dB

Pumford et al., 2000

Compared ITE and BTE performance Complex sound field (5 speakers) Improvement of 5.8 dB in SNR from omni

to directional for BTE Improvement of 3.3 dB in SNR from omni

to directional for ITE … but BTE had poorer omni performnace

to start with...

Novick et al, 2001

The signal processing scheme has no measurable impact of the directional mic benefit

Trade-off from two hearing aids (omni) to one hearing aid (directional)

Walter Reed group (JAAA)

Directional mode useful about 25% of the time (with experience);

User is capable of identifying environments where directional/ omnidirectional works best;

Report same level of satisfaction with either type of mic.

What’s going on in my lab?

North American Project

10 sites across the country 3 “subjects” at each site wearing a

single-mic design on one ear and a two-mic design on the other ear

dsp versus analog transparent to user Recheck of polars at 6, 12, 18 months (if

we get that far...)

Optimal pattern? (IJA)

Is one polar pattern superior either by group analysis or individual analysis?

25 subjects fit with each of five mic conditions (omni, cardioid, hyper, super, & “monofit”)

Field data thrown out Four directional conditions equal...

Results CST means and standard deviations for all subjects across

microphone conditions measured in the anechoic chamber with an 8-speaker “diffuse” field noise source.

Microphone Condition

Omni Monofit Cardioid Supercard Hypercard

Me

an

CS

T S

co

re (

rau

)

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Results HINT means and standard deviations for all subjects across

microphone condition measured in the anechoic chamber with an 8-speaker “diffuse” field noise source.

Microphone Condition

Omni Monofit Cardioid Supercard Hypercard

S/N

fo

r 5

0%

pe

rfo

rma

nce

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0

Adaptive Mic Effective?(JASA)

Is the dynamic mic design (as implemented in the ClaroTM) effective?

Ten subjects tested with BTEs in anechoic and reverb environments• noise only in rear plane

• overall 65 dBA but 2 second modulation (randomly) across five speakers

Configuration 10

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180195

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Results

Same performance with fixed as with dynamic mode

Yet, each subject wore HAs for 3-4 weeks in home environments

They noted the “directional benefit” just not a difference in benefit in the dynamic mode; validation of lab data

Digital noise reduction

Frequency(Hz)

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ON

ve

rsus

OF

F(o

utpu

t ch

ange

)

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random-85dB babble-85dB

Frequency(Hz)

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ON

ver

sus

OF

F(o

utpu

t ch

ange

)

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85dB random85dB babble

Frequency(Hz)

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DIF

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RE

NC

E (

dB

,1/3

octa

ve)

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85dB RANDOM 85dB BABBLE

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h v

ers

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utp

ut

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RANDOM BABBLE

Four approaches to reducing noise

Frequency(Hz)

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ve

rsu

s O

FF

(out

put

cha

nge

)

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SNR00 SNR05 SNR10 SNR15

85 dB

85 dB

Frequency(Hz)

125 250 500 1000 2000 4000 8000

DIF

FE

RE

NC

E (

dB

,1/3

octa

ve)

-35

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SNR0 SNR05 SNR10 SNR15

85 dB

Sonic RE#_100101842

/ Flat 50 dB Loss/ NR High/ Expansion OFF/85dB FONIX

Sonic RE#_100101842

/ Flat 50 dB Loss/ NR High/ Expansion OFF/85dB RANDOM

Sonic RE#_100101842

/ Flat 50 dB Loss/ NR High/ Expansion OFF/85dB BABBLE

WIDEX DIVA#_018524

/ Flat 50 dB Loss/ NR ON/ FEEDBACK CONTROL OFF/85dB FONIX

WIDEX DIVA#_018524

/ Flat 50 dB Loss/ NR ON/ FEEDBACK CONTROL OFF/85dB RANDOM

WIDEX DIVA#_018524

/ Flat 50 dB Loss/ NR ON/ FEEDBACK CONTROL OFF/85dB BABBLE

Total RMS power = -18.89

Total RMS = -26.29

Total RMS = -16.49


Depends on what you consider to be the advances…• Low/no distortion

• Wide bandwidth

• WDRC

• On-line fitting help

• Earmold-making techniques


Feedback supression• Yes, in many cases

Directional microphones• With training/practice

• Never as good as FM/ALD options Digital noise reduction

• For listening ease or comfort

• I’m still hopin’

Will technological advances improve the outcome?

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