michael syskind pedersen ph.d., hearing aid developer,...
TRANSCRIPT
Michael Syskind Pedersen
[Kuklasiński et al., 2016], [Kuklasiński and Jensen, 2017]
Local and binaural directicvity patterns
Michael Syskind Pedersen
Target direction = steering direction Steering direction = 0 degrees
Target direction (Azimuth angle) [degrees] Target direction (Azimuth angle) [degrees]
[Kuklasiński and Jensen, 2017]
Objective intelligibility prediction of MVDR + Single channel Post filter (MWF)
• Higher intelligibility using 4-microphone binaural MWF compared to two-microphone local MWF • 4-microphone binaural MWF has sensibility to steering vector errors (should be kept <15degrees) • High benefit of 4-microphone binaural MWF towards the sides compared to two-microphone local MWF
Local two microphone directivity
SNR improvement mainly of frontal talkers
Limited SNR improvement, when target is towards the side – especially in diffuse noise fields.
Michael Syskind Pedersen
Local directionality
Four microphone directivity
Possible to achieve a higher SNR
Possible to improve SNR for off-axis target sounds
Michael Syskind Pedersen
Binaural directionality
Four microphone directivity
Possible to achieve a higher SNR
Possible to improve SNR for off-axis target sounds
Risk of missing out target sound due to narrow beampatterns [Mejia et al. 2015]
Spatial cues affected
Off-target directions levels easily become too low – even though the SNR has been improved.
Michael Syskind Pedersen
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Binaural directionality
Michael Syskind Pedersen
Directional noise management system
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w1
w2
b
Fixed beamformers Adaptive beamformer
SNR Post filter
SNR estimate Noise removal
Example target talker direction
Front microphone
Rear microphone
Reaching the Opn directivity
• Early version • Good results in laboratory tests (ideal conditions), but…
• Beams were quite aggressive.
• Too much noise was removed also noise which did not have to be removed.
• Field test showed that end-users did not liked it.
• Possible reasons: • Insufficient loudness
• Awareness of the surroundings/Removed the ”good” noise
w1
w2
b
Fixed beamformers Adaptive beamformer
SNR Post filter
SNR estimate Noise reduction
Front microphone
Rear microphone
Problem: The omnidirectional response of a BTE
instrument tends to listen more backwards compared to the natural pinna response
Solution: Select a beamformer directivity pattern that
has similar properties as the natural pinna, i.e. a stable beampattern with a slight, frequency dependent dampening of sounds from the back.
0dB-5dB
-10dB-15dB
0dB-5dB
-10dB-15dB
0dB-5dB
-10dB-15dB
0dB-5dB
-10dB-15dB
BTE Pinna
Pinna BTE
Michael Syskind Pedersen
Directional system in easy enironments
w1
w2
b
Fixed beamformers Adaptive beamformer
SNR Post filter
SNR estimate Noise removal
Front microphone
Rear microphone
Automatic control
Reaching the Opn directivity
• We have a powerful machine which can remove a lot more noise.
• We had to turn it down. • Adapting the machinery to increase loudness and spatial awareness. • Many people preferred Pinna directionality in the majority of the time. • Noise reduction only to be applied, when it is needed. • Individual preferences. • Objective measures and models help, but cannot take us all the way. Fine tuning is subjective . • Noise management system should act as seamless as possible
Conclusions • Ability to reduce noise is important. • Even more important is knowing when to apply noise reduction
• How much noise reduction? • Individual differences
• The beamformer, which removes the most noise is not necessarily the one which people prefer • In the majority of the time, many hearing impaired prefer a stable beampattern that
do not remove too much noise.
• Binaural multi-microphone allows improves ability to remove noise • Narrow beams are not always good • The perceived sound environment will change much more aggressively the more
narrow the beam is, if the user and the environment are dynamic. • Tradeoff between SNR improvement and risk of removing target sound
References • A. Kuklasiński and J. Jensen “Multichannel Wiener Filters in Binaural and Bilateral Hearing Aids —
Speech Intelligibility Improvement and Robustness to DoA”, AES JOURNAL OF THE AUDIO ENGINEERING SOCIETY, vol. 65 no.1/2, pp. 8-16, Jan. 2017
• A. Kuklasiński, S. Doclo, S. H. Jensen, and J. Jensen, “Multichannel Wiener Filter for Speech Dereverberation in Hearing Aids—Sensitivity to DoA Errors,” presented at the AES 60th International Conference: DREAMS (Dereverberation and Reverberation of Audio, Music, and Speech), conference paper 2-2. 2016 Jan.
• Mejia et al., 2015: “Lost of speech perception in noise – cause and compensation”, Proceedings of the 5th symposium on Auditory and Audiological Research (ISAAR)