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Recent development in Recent development in hearing aid technologyhearing aid technology
Lena L N WongLena L N Wong
Division of Speech & Hearing Division of Speech & Hearing SciencesSciences
University of Hong KongUniversity of Hong Kong
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IntroductionIntroduction
Fixed directional microphoneFixed directional microphone How does it work?How does it work? Benefit Benefit Most preferred used environmentsMost preferred used environments LimitationsLimitations
Adaptive directional micAdaptive directional mic How does it work?How does it work? BenefitBenefit LimitationsLimitations
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Directional hearing aidsDirectional hearing aids Dual mic with signals froDual mic with signals fro
m back mic electronically m back mic electronically delayed and subtracted frdelayed and subtracted from that of front micom that of front mic
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Benefit of directional micBenefit of directional mic
1-16 dB improvement in SNR for 50% int1-16 dB improvement in SNR for 50% intelligibility elligibility (e.g., Ricketts, 2000; Valente et al., 2000)
3-5 dB improvement in real world (e.g3-5 dB improvement in real world (e.g.,., Ricketts et al., 2001)Ricketts et al., 2001)
Useful in about 1/3 of listening environmUseful in about 1/3 of listening environmentsents
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Evaluation of directional micEvaluation of directional mic
Older studies: single noise source in Older studies: single noise source in relatively non-reverberant relatively non-reverberant environments – not realistic environments – not realistic (Compton-Conley, 2004; Ricketts, 2000; Walden et al., 2000)
Real life situations: reverberation at Real life situations: reverberation at 300 to 1500 ms + varied room size, 300 to 1500 ms + varied room size, noise source and distancenoise source and distance
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Effect of various factors on benefiEffect of various factors on benefit of dir mic t of dir mic (Chung, 2004; Ricketts, 2000)
Multiple sources of noiseMultiple sources of noise
Noise from the front or aroundNoise from the front or around
Speech and noise outside critical Speech and noise outside critical distancedistance
ReverberationReverberation
minmin Vent sizeVent size
xx CompressionCompression
Switching between mic modesSwitching between mic modes
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Improvement in SNR comparing dImprovement in SNR comparing directional to omnidirectional micsirectional to omnidirectional mics
Data from Ricketts (2000)
Graph from Fabry (2004)
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How much do people use dir mic? How much do people use dir mic? (Cord et al., 2002)
Many (23% of new users) do not use dir Many (23% of new users) do not use dir modemode
Dir mode is used ¼ of the time in regular Dir mode is used ¼ of the time in regular users who switch between modes users who switch between modes
Why not use more often?Why not use more often? Can’t remember the difference between Can’t remember the difference between
programsprograms Dir mode not advantage over omniDir mode not advantage over omni Omni is the default settingOmni is the default setting
Despite differences in usage, users are just Despite differences in usage, users are just as satisfied with omni and dir modesas satisfied with omni and dir modes
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Most preferred use Most preferred use (Cord et al., 2002; Surr et al., 2002)
Directional mode if:Directional mode if: Talker is in frontTalker is in front Signal is nearSignal is near Background noise is non speechBackground noise is non speech Average size rooms, less reverberationAverage size rooms, less reverberation
Omni dir mode if:Omni dir mode if: Talker is behind or aroundTalker is behind or around No/minimum noiseNo/minimum noise Other people talking or sounds of natureOther people talking or sounds of nature Small space (e.g., cars)Small space (e.g., cars)
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Limitations of directional micLimitations of directional mic Increased internal mic noiseIncreased internal mic noise LF roll-off LF roll-off compensate to reduce tinny feeling compensate to reduce tinny feeling ( Rickett
s & Henry, 2002) more noise more noise Compensation if loss > 40 dB Compensation if loss > 40 dB (Ricketts & Henry, 2002) Provide partial compensationProvide partial compensation Use omni mic in quietUse omni mic in quiet
Wind noise (dir mic 20-30 dB more sensitive than omnWind noise (dir mic 20-30 dB more sensitive than omni)i)
Less sensitive to speech from backLess sensitive to speech from back Binaural cues may be affected Binaural cues may be affected (Kuk et al., 2002)
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Mic noise: omni vs directionalMic noise: omni vs directional
Kuk (2000)
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Limitations of dir micLimitations of dir mic Increased internal mic noiseIncreased internal mic noise LF roll-off LF roll-off compensate to reduce tinny feeling compensate to reduce tinny feeling ( Rickett
s & Henry, 2002) more noise more noise Compensation if loss > 40 dB Compensation if loss > 40 dB (Ricketts & Henry, 2002) Provide partial compensationProvide partial compensation Use omni mic in quietUse omni mic in quiet
Wind noise (dir mic 20-30 dB more sensitive than omnWind noise (dir mic 20-30 dB more sensitive than omni)i)
Less sensitive to speech from backLess sensitive to speech from back Binaural cues may be affected Binaural cues may be affected (Kuk et al., 2002)
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Low frequency roll off in dir Low frequency roll off in dir aidsaids
Thompson (2000)
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Limitations of dir micLimitations of dir mic Increase internal mic noiseIncrease internal mic noise LF roll-off LF roll-off compensate to reduce tinny feeling compensate to reduce tinny feeling ( Rick
etts & Henry, 2002) more noise more noise Compensation if loss > 40 dB Compensation if loss > 40 dB (Ricketts & Henry, 2002) Provide partial compensationProvide partial compensation Use omni mic in quietUse omni mic in quiet
Wind noise (dir mic 20-30 dB more sensitive than omWind noise (dir mic 20-30 dB more sensitive than omni) ni) (Chung, 2005)
Less sensitive to speech from backLess sensitive to speech from back Binaural cues may be affected Binaural cues may be affected (Kuk et al., 2002)
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Turbulence on the downwind Turbulence on the downwind side as wind blows past the side as wind blows past the headhead
Figure from DFigure from Dillon, Roe, anillon, Roe, and Katsch (199d Katsch (1999) as appeare9) as appeared in Thompsod in Thompson (2000)n (2000)
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Wind noise: omni vs dirWind noise: omni vs dir
Kuk (2000)
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Limitations of dir micLimitations of dir mic Increase internal mic noiseIncrease internal mic noise LF roll-off LF roll-off compensate to reduce tinny feeling compensate to reduce tinny feeling ( Rickett
s & Henry, 2002) more noise more noise Compensation if loss > 40 dB Compensation if loss > 40 dB (Ricketts & Henry, 2002) Provide partial compensationProvide partial compensation Use omni mic in quietUse omni mic in quiet
Wind noise (dir mic 20-30 dB more sensitive than omnWind noise (dir mic 20-30 dB more sensitive than omni) i) (Chung, 2005)
Less sensitive to speech from backLess sensitive to speech from back Binaural cues may be affected Binaural cues may be affected (Kuk et al., 2002)
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Front to back ratioFront to back ratio
From Phonak
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Limitations of dir micLimitations of dir mic Increase internal mic noiseIncrease internal mic noise LF roll-off LF roll-off compensate to reduce tinny feeling compensate to reduce tinny feeling ( Rickett
s & Henry, 2002) more noise more noise Compensation if loss > 40 dB Compensation if loss > 40 dB (Ricketts & Henry, 2002) Provide partial compensationProvide partial compensation Use omni mic in quietUse omni mic in quiet
Wind noise (dir mic 20-30 dB more sensitive than omnWind noise (dir mic 20-30 dB more sensitive than omni) i) (Chung, 2005)
Less sensitive to speech from backLess sensitive to speech from back Binaural cues may be affected Binaural cues may be affected (Kuk et al., 2002)
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A few caveats A few caveats (Chung, 2005)
Move away from reflective surface to reducMove away from reflective surface to reduce reverberatione reverberation
Compensate for LF gain if loss > 40 dB HL; tCompensate for LF gain if loss > 40 dB HL; turn off if needed urn off if needed (Ricketts & Henry, 2002)
Use omni in quiet, dir in noise with speech Use omni in quiet, dir in noise with speech from frontfrom front
Mic matching Mic matching to within .02 dB and 1 degreto within .02 dB and 1 degree (e ( adaptive mic matching) adaptive mic matching)
Examine mic for debrisExamine mic for debris
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Effect of Effect of microphonmicrophone mismatche mismatch
Kuk (2000)
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Adaptive dir micAdaptive dir mic
Internal delay altered Internal delay altered vary directi vary directional pattern to yield the lowest outonal pattern to yield the lowest outputput
Takes 4 - 10 sec to change from omni to Takes 4 - 10 sec to change from omni to dir, 10 msec - 5 sec to change between pdir, 10 msec - 5 sec to change between polar patternsolar patterns
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Are adaptive directional mic betteAre adaptive directional mic better than fixed direction mic?r than fixed direction mic? Not worse!Not worse! Depends on the noise condition:Depends on the noise condition:
Better when noise is on the side, from a narrBetter when noise is on the side, from a narrow spatial angle and changing direction ow spatial angle and changing direction (e.g., Valente & Mispagel, 2004; Ricketts et al., 2003)
Same when noise is from a wide spatial anglSame when noise is from a wide spatial angle or multiple noise sources e or multiple noise sources (e.g., Bentler et al., 2004)
Difficult for users to perceive a difference between fixed and adaptive dir mic modes but adaptive dir mic is described more favorably (Surr, 2002)
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SNR improvement comparing adaptivSNR improvement comparing adaptive dir, fixed dir and omni dir micse dir, fixed dir and omni dir mics
Data from Ricketts & Henry (2002)
Graph from Fabry (2004)
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Limitations with adaptive dir Limitations with adaptive dir micmic Synchronization between ears may yield Synchronization between ears may yield
the best benefit but not doing so does not the best benefit but not doing so does not degrade performancedegrade performance
Payne & Lutman (2002)
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Broadband (single polar pattern across freqBroadband (single polar pattern across frequencies) vs multiband (polar patterns at variuencies) vs multiband (polar patterns at various frequency bands varied with noise)ous frequency bands varied with noise)
Fabry (2004)
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LimitationsLimitations
When adjustment of the adaptive When adjustment of the adaptive algorithm is not fast enough algorithm is not fast enough compared to changes in direction of compared to changes in direction of noisenoise
Multiple noise sources particularly Multiple noise sources particularly when spectra & level of noise when spectra & level of noise sources are similar sources are similar (Bentler et al., 2003; Bentler et al., 2004)
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Second order dir micSecond order dir mic 3 mic3 mic Performance with 3 mic Performance with 3 mic
better but not statisticalbetter but not statistically different from 2 micly different from 2 mic (Ricketts et al., 2003)
Big LF roll-off 12 dB/octBig LF roll-off 12 dB/octave + high noiseave + high noise 2 mic < 1000 Hz, 3 mic > 12 mic < 1000 Hz, 3 mic > 1
000 Hz000 Hz
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Directional hearing aids for Directional hearing aids for children?children? Head turn to sound source (> age 4 ok)Head turn to sound source (> age 4 ok) Reduced low frequency gain in dir modeReduced low frequency gain in dir mode Incidental learning (from the back)Incidental learning (from the back) Self-monitoring of speechSelf-monitoring of speech SafetySafety Profound loss not usefulProfound loss not useful Selection of mic directivitySelection of mic directivity Accuracy of adaptive micAccuracy of adaptive mic
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Which mic system to use?Which mic system to use?
Fabry (2004)
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SummarySummary
Helps with speech in front, noise from bHelps with speech in front, noise from back with minimal reverberationack with minimal reverberation
Major limitations: mic noise, LF roll off, Major limitations: mic noise, LF roll off, wind noise, speech from backwind noise, speech from back
Adaptive mic may be preferred; useful in Adaptive mic may be preferred; useful in noise from narrow spatial ange noise from narrow spatial ange
Can be used in older childrenCan be used in older children
