US 6,480,610 B1Granted

Subband acoustic feedback cancellation in hearing aids

AssigneeSonic Innovations, Inc.

InventorsXiaoling Fang, Gerald Wilson, Brad Giles

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Abstract

A new subband feedback cancellation scheme is proposed, capable of providing additional stable gain without introducing audible artifacts. The subband feedback cancellation scheme employs a cascade of two narrow-band filters Ai(Z) and Bi(Z) along with a fixed delay, instead of a single filter Wi(Z) and a delay to represent the feedback path in each subband. The first filter, Ai(Z), is called the training filter, and models the static portion of the feedback path in ith subband, including microphone, receiver, ear canal resonance, and other relatively static parameters. The training filter can be implemented as a FIR filter or as an IIR filter. The second filter, BI(Z), is called a tracking filter and is typically implemented as a FIR filter with fewer taps than the training filter. This second filter tracks the variations of the feedback path in the ith subband caused by jaw movement or objects close to the ears of the user.

Claims24

Dependent claims

A method for canceling acoustic feedback in hearing aids, comprising the steps of:

digitizing an input audio signal into a sequence of digital audio samples;
splitting said sequence of digital audio samples into a plurality of subband signals;
processing each of said plurality of subband signals separately with a noise reduction and hearing loss compensation algorithm into a plurality of processed digital subband audio signals;
combining said plurality of processed digital subband audio signals into a processed wideband digital audio signal;
converting said processed wideband digital audio signal into an output audio signal;
splitting said processed wideband digital audio signal into a plurality of subband feedback signals;
filtering each of said plurality of subband feedback signals with a narrow-band training filter that models the static portion of the feedback path in each of said subbands and provides an output thereof;
filtering each said output of said narrow-band training filter with a narrow-band tracking filter that tracks the variations of the feedback path in each of said subbands, and provides an output thereof, and
subtracting said output of each of said narrow-band tracking filters from the corresponding subband signal of said plurality of subband signals.

6 more elements

An apparatus for canceling acoustic feedback in hearing aids, comprising:

an analog to digital converter for digitizing an input audio signal into a sequence of digital audio samples;
a first analysis filter bank for splitting said sequence of digital audio samples into a plurality of subbands, wherein each of said subbands outputs a corresponding subband signal;
a subtractor in each of said subbands that subtracts the output of each of a plurality of narrow-band tracking filters from a corresponding subband signal at the output of said first analysis filter bank;
a digital signal processor in each of said subbands that processes the output of said subtractor with a noise reduction and hearing loss compensation algorithm into a plurality of processed digital subband audio signals;
a synthesis filter bank for combining said plurality of processed digital subband audio signals into a processed wideband digital audio signal;
a digital to analog converter for converting said processed wideband digital audio signal into an output audio signal;
a second analysis filter bank for splitting said processed wideband digital audio signal into said plurality of subbands, wherein each of said subbands outputs a corresponding subband feedback signal;
a narrow-band training filter coupled to each of said plurality of subband feedback signals that models the static portion of the feedback path in each of said subbands and provides an output thereof;
and
a narrow-band tracking filter coupled to the output of each of said narrow-band training filters that tracks the variations of the feedback path in each of said subbands and provides an output to said subtractor.

7 more elements

An apparatus for canceling acoustic feedback in hearing aids, comprising:

an analog to digital converter for digitizing an input audio signal into a sequence of digital audio samples;
a first analysis filter bank for splitting said sequence of digital audio samples into a plurality of subbands, wherein each of said subbands outputs a corresponding subband signal;
a subtractor in each of said subbands that subtracts the output of each of a plurality of narrow-band tracking filters from a corresponding subband signal at the output of said first analysis filter bank;
a digital signal processor in each subband that processes output of said subtractor with a noise reduction and hearing loss compensation algorithm into a plurality of processed digital subband audio signals;
a plurality of noise matching filters, wherein each said noise matching filter is associated with one of said processed digital subband audio signals, and wherein said plurality of noise matching filters are stimulated by a noise generator;
a synthesis filter bank having a multiplexing switch coupled to the input of said synthesis filter bank, wherein said multiplexing switch selectively couples either one of said processed digital subband audio signals or the output of the corresponding noise matching filter to the input of said synthesis filter bank, and wherein said synthesis filter bank combines either said processed digital subband audio signals into a processed wideband digital audio signal or the outputs of said noise matching filters into a processed wideband digital audio signal;
a digital to analog converter for converting said processed wideband digital audio signal into an output audio signal;
a second analysis filter bank for splitting said processed wideband digital audio signal into said plurality of subbands, wherein each of said subbands outputs a corresponding subband feedback signal;
a narrow-band training filter coupled to each of said plurality of subband feedback signals that models the static portion of the feedback path in each of said subbands and provides an output thereof;
and
a narrow-band tracking filter coupled to the output of each of said narrow-band training filters that tracks the variations of the feedback path in each of said subbands and provides an output to said subtractor.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/399,483Filed 21 Sep 1999
Granted: 12 Nov 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

H04R 25/453
Prevention of acoustic reaction, i.e. acoustic oscillatory feedback: electronically
H04R 25/505
Customised settings for obtaining desired overall acoustical characteristics: using digital signal processing
H04R 2430/03
Signal processing covered by H04R, not provided for in its groups: synergistic effects of band splitting and sub-band processing
H04R
Loudspeakers, microphones, gramophone pick-ups or like acoustic electromechanical transducers