Hearing aid

• US 20020057814A1
• Filed: 11/29/2000
• Published: 05/16/2002
• Est. Priority Date: 09/25/2000
• Status: Active Grant

• Current Assignee: Widex A/S (WS Audiology A/S)
• Original Assignee: Widex A/S (WS Audiology A/S)
• Inventors: Kaulberg, Thomas
• Granted Patent: US 6,738,486 B2
• Time in Patent Office: Days
• US Class Current: 381/312
• CPC Class Codes: H04R 25/353 Frequency, e.g. frequency shift or compression
• CPC Class Codes: H04R 25/453 electronically
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

The present invention relates to a hearing aid with an adaptive filter for suppression of acoustic feedback in the hearing aid. The hearing aid further comprises a controller that is adapted to compensate for acoustic feedback by determination of a first parameter of an acoustic feedback loop of the hearing aid and adjustment of a second parameter of the hearing aid in response to the first parameter whereby generation of undesired sounds is substantially avoided. Hereby a gain safety margin requirement is significantly reduced.

Claims

1. A hearing aid comprising

an input transducer for transforming an acoustic input signal into a first electrical signal,

a first filter bank with bandpass filters for dividing the first electrical signal into a set of bandpass filtered first electrical signals,

a processor for generation of a second electrical signal by individual processing of each of the bandpass filtered first electrical signals and adding the processed electrical signals into the second electrical signal,

an output transducer for transforming the second electrical signal into an acoustic output signal,

a second filter bank with bandpass filters for dividing the second electrical signal into a set of bandpass filtered second electrical signals,

a first set of adaptive filters with first filter coefficients for estimation of acoustic feedback by generation of third electrical signals by filtering of the bandpass filtered second electrical signals and adapting the respective third signals to respective signals on the input side of the processor with respective first convergence rates, and

a controller that is adapted to compensate for acoustic feedback by determination of a first parameter of an acoustic feedback loop of the hearing aid and adjustment of a second parameter of the hearing aid in response to the first parameter whereby generation of undesired sounds is substantially avoided.

2. A hearing aid according to claim 1, wherein at least one of the adaptive filters of the first set of adaptive filters operates on a respective decimated bandpass filtered second electrical signal.

3. A hearing aid according to claim 1, wherein the first filter bank consists of a single bandpass filter.

4. A hearing aid according to claim 1, wherein the second filter bank consists of a single bandpass filter, and the first set of adaptive filters consists of a single adaptive filter.

5. A hearing aid according to claim 1, wherein the bandpass filters of the second filter bank are substantially identical to respective bandpass filters of the first filter bank.

6. A hearing aid according to claim 4, wherein the first set of adaptive filters filters the second electrical signal and adapts to the first electrical signal.

7. A hearing aid according to claim 6, further comprising a combining node for subtraction of the third signal from the first electrical signal, and wherein the subtracted signal is fed to the processor.

8. A hearing aid according to claim 5, wherein the first set of adaptive filters filters the respective bandpass filtered second electrical signals and adapts to the respective bandpass filtered first electrical signals.

9. A hearing aid according to claim 8, further comprising a combining node for subtraction of the third signals from the respective bandpass filtered first electrical signals, and wherein the subtracted signals are fed to the processor.

10. A hearing aid according to claim 6, further comprising

a second adaptive filter with second filter coefficients for suppression of feedback in the hearing aid by filtering the second electrical signal into a fourth electrical signal,

a combining node for generation of a fifth electrical signal by subtraction of the fourth electrical signal from the first electrical signal and for feeding the fifth electrical signal to the respective bandpass filters of the first filter bank, and wherein the second filter coefficients are updated with a second convergence rate that is lower than the first convergence rate.

11. A hearing aid according to claim 8, further comprising

a set of second adaptive filters with second filter coefficients for suppression of feedback in the hearing aid by filtering the bandpass filtered second electrical signals into respective fourth electrical signals,

a combining node for generation of fifth electrical signals by subtraction of the fourth electrical signals from the respective bandpass filtered first electrical signals and for feeding the fifth electrical signals to the processor, and wherein the second filter coefficients are updated with a second convergence rate that is lower than the first convergence rate.

12. A hearing aid according to claim 1, wherein the first parameter is an operating gain of the processor.

13. A hearing aid according to claim 1, wherein the first parameter is a parameter of the first set of adaptive filters.

14. A hearing aid according to claim 13, wherein the first parameter is the ratio between the magnitude of a signal at an input of a first adaptive filter of the first set of adaptive filters and the magnitude of a signal at the corresponding output.

15. A hearing aid according to claim 1, wherein the second parameter is a gain of the processor.

16. A hearing aid according to claim 1, wherein the second parameter is the first convergence rate of the first filter coefficients.

17. A hearing aid according to claim 10, wherein the second parameter is the second convergence rate of the second filter coefficients.

18. A hearing aid according to claim 1, further comprising means for updating filter coefficients according to a leaky least mean square algorithm:

c_i(n+1)=λ

(c_i(n)−

c_i(0))+c_i(0)+μ

u_i(n)e(n)

where c_i(n+1) is the updated value of i'"'"'th filter coefficient, c_i(n) is the current value of the i'"'"'th filter coefficient, c_i(0) is the initial value of the i'"'"'th filter coefficient, u_i(n) is the (n-i)'"'"'th sample of the processor output signal, e(n) is the current sample of the second electrical signal, λ

is the leakage, and μ

is the convergence, λ and

μ

determining the first convergence rate.

19. A hearing aid according to claim 1, further comprising means for updating filter coefficients according to a normalized Least Mean Square:

c(n+1)=λ

(c(n)−

c(0))+c(0)+$\underset{\_}{c}<br><br>\left(n+1\right)=\mathrm{\lambda <br><br>}<br><br>\left(\underset{\_}{c}<br><br>\left(n\right)-\underset{\_}{c}<br><br>\left(0\right)\right)+\underset{\_}{c}<br><br>\left(0\right)+\mathrm{\mu <br><br>}<br><br>\frac{\underset{\_}{u}<br><br>\left(n\right)}{\underset{\_}{u}<br><br>\left(n\right)·<br><br>\underset{\_}{u}<br><br>\left(n\right)}<br><br>e<br><br>\left(n\right)$

where u(n) is an N dimensional vector containing the latest N samples of the signal u, c(n) is a vector containing the current values of the N filter coefficients, c(0) is a vector containing the initial values of the N filter coefficients, c(n+1) is the updated values of the N filter coefficients, and e(n) is the current sample of the second electrical signal.

20. A hearing aid according to claim 1, further comprising means for updating filter coefficients according to a power normalized Least Mean Square algorithm.

P_u(t+T)=α

P_u(t)+(1−

α

)u²(t)

where α

is a predetermined constant that determines the rate with which the P_u estimate changes.

21. A hearing aid according to claim 1, further comprising means for updating filter coefficients according to a leaky sign least mean square algorithm:

c_l(n+1)=λ

(c_i(n)−

c_l(0))+c_i(0)+μ

_su_i(n)

where c_l(n+1) is the updated value of i'"'"'th filter coefficient, c_i(n) is the current value of the i'"'"'th filter coefficient, c_l(0) is the initial value of the i'"'"'th filter coefficient, u_i(n) is the (n-i)'"'"'th sample of the processor output signal, e(n) is the current sample of the second electrical signal, λ

is the leakage, and μ

is the convergence, and μ

_s is the sign of the e(n) signal multiplied by μ

, λ and

μ

determining the first convergence rate.

22. A hearing aid according to claim 1, further comprising means for updating filter coefficients according to a leaky sign-sign least mean square algorithm:

c_i(n+1)=λ

(c_i(n)−

c_i(0))+c_i(0)+μ

_ssgn(u_i(n))

where c_i(n+1) is the updated value of i'"'"'th filter coefficient, c_i(n) is the current value of the i'"'"'th filter coefficient, c_i(0) is the initial value of the i'"'"'th filter coefficient, u_i(n) is the (n-i)'"'"'th sample of the processor output signal, e(n) is the current sample of the second electrical signal, λ

is the leakage, and μ

is the convergence factor, and sgn(u_l(n)) is the sign of u_i(n), λ and

μ

determining the first convergence rate.

23. A hearing aid according to claim 1, wherein at least one of the first and second sets of adaptive filters comprises a finite impulse response filter.

24. A hearing aid according to claim 1, wherein at least one of the first and second sets of adaptive filters comprises a warped finite impulse response filter.

25. A hearing aid according to claim 1, wherein the controller is adapted to adjust a second parameter of the hearing aid in response to the first parameter and in response to the actual acoustic environment.

27. A hearing aid according to claim 26, wherein the warped filter is a warped FIR filter.

26. A hearing aid comprising

an input transducer for transforming an acoustic input signal into a first electrical signal,

a processor for generation of a second electrical signal by processing of the first electrical signals into the second electrical signal,

an output transducer for transforming the second electrical signal into an acoustic output signal,

an adaptive filter with filter coefficients for estimation of acoustic feedback by generation of third electrical signals by filtering of the second electrical signal and adapting the respective third signals to respective signals on the input side of the processor,

characterised in that

the adaptive filter is a warped adaptive filter.

28. A method of suppressing acoustic feedback in a hearing aid, comprising the steps of:

transforming an acoustic input signal into a first electrical signal,

dividing the first electrical signal into a set of bandpass filtered first electrical signals,

processing each of the bandpass filtered first electrical signals individually,

adding the processed electrical signals into a second electrical signal,

transforming the second electrical signal into an acoustic output signal,

dividing the second electrical signal into a set of bandpass filtered second electrical signals,

estimating acoustic feedback by generation of third electrical signals by adaptive filtering of the bandpass filtered second electrical signals and adapting the filtered signals to respective signals on the input side of the processor with respective first convergence rates, and

compensating for acoustic feedback by

determining a first parameter of an acoustic feedback loop of the hearing aid, and

adjusting a second parameter of the hearing aid in response to the first parameter

whereby generation of undesired sounds is substantially avoided.