Post on 04-Jan-2016
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
0.2
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Adaptive Directionality
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Adaptive Directionality
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Adaptive Directionality
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Adaptive Directionality90
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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 con- ditions (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
)
60
70
80
90
100
110
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
-7
-6
-5
-4
-3
-2
-1
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
1530
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135
150165
180195
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330345
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)
125 250 500 1000 2000 4000 8000
ON
ve
rsus
OF
F(o
utpu
t ch
ange
)
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
random-85dB babble-85dB
Frequency(Hz)
125 250 500 1000 2000 4000 8000
ON
ver
sus
OF
F(o
utpu
t ch
ange
)
-10
-8
-6
-4
-2
0
2
85dB random85dB babble
Frequency(Hz)
125 250 500 1000 2000 4000 8000
DIF
FE
RE
NC
E (
dB
,1/3
octa
ve)
-40
-30
-20
-10
0
10
85dB RANDOM 85dB BABBLE
Frequency(Hz)
125 250 500 1000 2000 4000 8000
Hig
h v
ers
us
OF
F(o
utp
ut
cha
nge
)
-10
-8
-6
-4
-2
0
2
RANDOM BABBLE
Four approaches to reducing noise
Frequency(Hz)
125 250 500 1000 2000 4000 8000
ON
ve
rsu
s O
FF
(out
put
cha
nge
)
-16
-14
-12
-10
-8
-6
-4
-2
0
2
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
-30
-25
-20
-15
-10
-5
0
5
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
Will technological advances improve the outcome?
Depends on what you consider to be the advances…• Low/no distortion
• Wide bandwidth
• WDRC
• On-line fitting help
• Earmold-making techniques
Will technological advances improve the outcome?
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’