Directivity for real world benefit

Michael Syskind Pedersen Ph.D., Hearing aid developer, Oticon

Michael Syskind Pedersen

Front microphone

Rear microphone

Available microphones for directionality

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

8

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)