HEARING AID SYSTEM WITH FEEDBACK ARRANGEMENT TO PREDICT AND CANCEL ACOUSTIC FEEDBACK, METHOD AND USE

• US 20100254555A1
• Filed: 09/30/2008
• Published: 10/07/2010
• Est. Priority Date: 10/03/2007
• Status: Active Grant

• Current Assignee: Oticon A/S (William Demant Fonden)
• Original Assignee: Oticon A/S (William Demant Fonden)
• Inventors: Elmedyb, Thomas Bo, Hellgren, Johan
• Granted Patent: US 8,687,832 B2
• Time in Patent Office: Days
• US Class Current: 381/318
• CPC Class Codes: H04R 25/453 electronically

Abstract

The invention relates to a hearing aid system with an electrical feedback cancellation path, for compensating acoustic feedback between an output transducer and an input transducer by subtracting an estimate of the acoustical feedback from a signal on the input side of the amplifier part, the electrical feedback cancellation path comprising an adaptive filter for providing a variable filtering function. The invention further relates to a method of compensating acoustic feedback in a hearing aid system and to its use. The object of the present invention is to provide an alternative scheme for estimating the acoustical/mechanical feedback in a hearing aid. The problem is solved in that the hearing aid system comprises a second electrical input signal consisting essentially of the direct part of said first electrical input signal (i.e. without acoustic feedback), and wherein the second electrical input signal is used to influence, preferably enhance, the filtering function of the adaptive filter of the feedback cancellation path. Preferably, the system comprises a second input transducer for generating the second electrical input signal, the second input transducer being spatially located at a position where the amplitude of the acoustical signal from the output transducer at a given frequency is smaller than at the location of the first input transducer, and wherein the electrical signal of the second input transducer is used to adapt the filtering function of the adaptive filter. Preferably, the signal path comprises a generator of an electrical probe signal for use in characterizing the feedback path. The invention may e.g. be used in binaural hearing aid systems or in connection with other electronic devices comprising a second electrical input signal, e.g. generated by a microphone separately located from a first microphone of the hearing aid.

Claims

1. A hearing aid system comprising

a) a first input transducer for converting an acoustical signal to a first electrical input signal comprising a direct part and an acoustical feedback part,

b) an output transducer for generating an acoustical signal from an electrical output signal,

c) an electrical signal path being defined between the input transducer and the output transducer and comprising a signal processing unit including an amplifier part for enabling frequency dependent gain of an input signal, the amplifier part defining an input side of the signal path between the input transducer and the amplifier part and an output side of the signal path between the amplifier part and the output transducer,

d) an electrical feedback cancellation path between the output side and the input side of the signal path for compensating acoustic feedback between the output transducer and the input transducer by subtracting an estimate of the acoustical feedback from a signal on the input side of the amplifier part, the electrical feedback cancellation path comprising an adaptive filter for providing a variable filtering function,

the hearing aid system being

further adapted to provide a second electrical input signal essentially consisting of the direct part of said first electrical input signal, when the hearing aid system is in use, and the adaptive filter of the feedback cancellation path is adapted to use a signal derived from the second electrical input signal to influence, preferably enhance, its filtering function.

2. A hearing aid system according to claim 1 wherein the adaptive filter of the electrical feedback cancellation path comprises a variable filter part for providing a frequency dependent filtering function and a control part for controlling the characteristics of the frequency dependent filtering function.

3. A hearing aid system according to claim 1 or 2 wherein a signal based on the second electrical input signal is subtracted from the feedback corrected input signal from the first input transducer and the resulting signal is fed to the control part of the adaptive filter of the electrical feedback cancellation path and used to adapt the filtering function of the adaptive filter.

4. A hearing aid system according to claim 1, comprising a second input transducer for converting an acoustical signal to said second electrical input signal, the second input transducer being located at a position where the acoustical signal is substantially free from acoustic feedback from the output transducer.

5. A hearing aid system according to claim 1, comprising a probe signal generator for generating a probe signal for use in characterizing the acoustical feedback path.

6. A hearing aid system according to claim 5 wherein the probe signal is fed to the control part of the adaptive filter and used to adapt the filtering function of the adaptive filter.

7. A hearing aid system according to claim 4 comprising a compensation of the delay of the signal from the first to the second input transducer and from the second input transducer to the signal processing part of the hearing aid system.

8. A hearing aid system according to claim 1 comprising a feedback enhancer unit in the form of a second adaptive filter for estimating the difference in path from the source to the first and second input transducers, respectively, and from the second input transducer to the feedback enhancer.

9. A hearing aid system according to claim 4 wherein the first and second input transducers are located in two physically separate bodies.

10. A hearing aid system according to claim 1 comprising first and second hearing instruments, one for each ear of a wearer, wherein the first transducer forms part of the first hearing instrument, and the second input transducer is an input transducer of the second hearing instrument.

11. A hearing aid system according to claim 1 wherein the second input transducer is a microphone of some other apparatus with which the hearing aid can communicate.

12. A hearing aid system according to claim 1 wherein the second electrical input signal is fed to a feedback enhancer unit for preparing the derived signal from the second electrical input signal to influence, preferably enhance, the filtering function of the adaptive filter of the electrical feedback cancellation path.

19. Use a hearing aid system according to claim 1.

13. A method of compensating acoustic feedback in a hearing aid system comprising

a) providing a first input transducer for converting an acoustical signal to a first electrical input signal comprising a direct part and an acoustic feedback part,

b) providing an output transducer for generating an acoustical signal from an electrical output signal,

c) providing an electrical signal path between the input transducer and the output transducer, the signal path comprising a signal processing unit including an amplifier part for enabling frequency dependent gain of an input signal, the amplifier part defining an input side of the signal path between the input transducer and the amplifier part and an output side of the signal path between the amplifier part and the output transducer,

d) providing an electrical feedback cancellation path between the output side and the input side of the signal path for compensating acoustic feedback between the output transducer and the input transducer by subtracting an estimate of the acoustical feedback from a signal on the input side of the amplifier part, the electrical feedback cancellation path comprising an adaptive filter for providing a variable filtering function,

f) providing a second electrical input signal substantially free from acoustic feedback from the output transducer, and

g) providing that the second electrical input signal is used to influence, preferably enhance, the filtering function of the adaptive filter of the feedback cancellation path.

14. A method according to claim 13 comprising h1) providing that the second electrical input signal is generated by a second input transducer for converting an acoustical signal to an electrical signal, and providing that the second input transducer is located at a position where the amplitude of the acoustical signal from the output transducer is attenuated (preferably substantially eliminated), e.g. a factor of more than 10, such as more than 100, such as more than 1000, compared to the level at first input transducer.

15. A method according to claim 13 or 14 comprising h2) providing a generator of an electrical probe signal for use in characterizing the feedback path, wherein the probe signal is fed to the adaptive filter and used to adapt the filtering function of the adaptive filter.

16. A method according to claim 13 wherein a compensation of the delay of the signal from the first to the second input transducer and back to the signal processing part of the hearing aid system is provided.

17. A method according to claim 13 wherein a second adaptive filter for estimating the difference in path from the source to the first and second input transducers, respectively, and back to the signal processing part of the hearing aid system is provided.

18. A method according to claim 13 wherein the signal from the second input transducer wirelessly transmitted e.g. streamed, to the signal processing part of the hearing aid system.

20. A hearing aid system comprising

a) a first input transducer for converting an acoustical signal to a first electrical input signal comprising a direct or external part and an acoustical feedback part,

b) an output transducer for generating an acoustical signal from an electrical output signal,

c) an electrical signal path being defined between the input transducer and the output transducer and comprising a signal processing unit including an amplifier part for enabling frequency dependent gain of an input signal, the amplifier part defining an input side of the signal path between the input transducer and the amplifier part and an output side of the signal path between the amplifier part and the output transducer,

d) an electrical feedback cancellation path between the output side and the input side of the signal path for compensating acoustic feedback between the output transducer and the input transducer by subtracting an estimate of the acoustical feedback from a signal on the input side of the amplifier part, the electrical feedback cancellation path comprising an adaptive filter for providing a variable filtering function,

e) a feedback enhancer unit, providing an output signal for improving the estimate of the feedback cancellation path made by the adaptive filter, the output of the feedback enhancer unit constituting an estimate of the direct or external part of the first electrical input signal, the hearing aid system being further adapted to provide a second electrical input signal from which the the direct or external part of said first electrical input signal can be estimated, second electrical input signal being connected to the feedback enhancer unit.