Method for feedback cancelling in a hearing device and a hearing device

1. A method for cancelling or preventing feedback in a hearing device comprising a microphone ( 1 ), a transfer function ( 2 ) and a receiver ( 3 ), wherein the transfer function ( 2 ) defines relation between an input signal ( 12 ) of the hearing device and an output signal ( 13 , 13 ′) of the hearing device, the method comprising the steps of:

estimating an external transfer function ( 21 ) of an external feedback path ( 11 ) defined by sound traveling from the receiver ( 3 ) to the microphone ( 1 ),

characterized by comprising the steps of

estimating the input signal ( 12 ′) having no feedback components of the external feedback path ( 11 ) using an auxiliary signal ( 15 ) comprising no feedback components of the external feedback path ( 11 ), and

using the estimated input signal ( 14 ) for estimating the external transfer function ( 21 ) of the external feedback path ( 11 ).

2. The method of claim 1 , characterized in that an adaptive filter (AF) using a Least-Mean-Square algorithm is implemented for estimating the external transfer function ( 21 ).

3. The method of claim 1 , characterized by further comprising the steps of

calculating an estimated feedback signal ( 22 ) using the estimated external transfer function ( 7 ) and the output signal ( 13 ) of the hearing device, and

subtracting the estimated feedback signal ( 22 ) from an output signal of the microphone ( 1 ), the result of subtracting the estimated feedback signal ( 22 ) from the output signal of the microphone ( 1 ) being used to adjust the estimated external transfer function ( 7 ).

4. The method of claim 1 , characterized in that one of the following signals is used as auxiliary signal ( 15 ):

an output signal of a microphone of a contra-lateral hearing device;

a combination of output signals of a contra-lateral or a remote microphone;

a signal picked-up by a remote microphone.

5. The method of claim 1 , characterized in that a further adaptive filter ( 20 ) preferably using a Least-Mean-Square algorithm is implemented for estimating the input signal ( 12 ′) having no feedback components.

6. The method of claim 1 , characterized by further comprising the step of using the input signal ( 12 ) of the hearing device for estimating the input signal ( 12 ′) having no feedback components.

7. The method of claim 3 , characterized by further comprising the step of subtracting the estimated input signal ( 14 ) weighted by a first factor (k 1 ) from the result of subtracting the estimated feedback signal ( 22 ) from the output signal ( 12 ) of the microphone ( 1 ), the first factor (k 1 ) having a value between 0 and 1, preferably a value of 0.9.

8. The method of claim 3 , characterized by further comprising the step of subtracting the estimated input signal ( 14 ) or a processed estimated input signal ( 14 ) from the output signal ( 13 ), the estimated input signal ( 14 ) or the processed estimated input signal ( 14 ) being weighted by a second factor (k 2 ) that has a value between 0 and 1, preferably a value of 0.1.

9. The method of claim 7 , characterized by involving the transfer function ( 2 ) in the processing of the estimated input signal ( 14 ).

10. A hearing device comprising

a microphone ( 1 ),

a transfer function unit ( 2 ) having a transfer function,

a receiver ( 3 ),

means for estimating an external transfer function ( 21 ) of an external feedback path ( 11 ) defined by sound traveling from the receiver ( 3 ) to the microphone ( 1 ),

wherein the transfer function defines relation between an input signal ( 12 ) of the hearing device and an output signal ( 13 , 13 ′) of the hearing device, characterized by further comprising

means for estimating the input signal ( 12 ′) having no feedback components of the external feedback path ( 11 ) using an auxiliary signal ( 15 ) comprising no feedback components of the external feedback path ( 11 ), and

operationally connecting the estimated input signal ( 14 ) to the means for estimating the external transfer function ( 21 ) of the external feedback path ( 11 ).

11. The hearing device of claim 10 , characterized by further comprising

means for calculating an estimated feedback signal ( 22 ) using the estimated external transfer function ( 7 ) and the output signal ( 13 ) of the hearing device, and

means for subtracting the estimated feedback signal ( 22 ) from an output signal of the microphone ( 1 ), the result of subtracting the estimated feedback signal ( 22 ) from the output signal of the microphone ( 1 ) being used to adjust the estimated external transfer function ( 7 ).

12. The hearing device of claim 10 , characterized in that the auxiliary signal ( 15 ) is one of the following signals:

an output signal of a microphone of a contra-lateral hearing device;

a combination of output signals of a contra-lateral or remote microphone;

a signal picked-up by a remote microphone.

13. The hearing device of claim 10 , characterized in that the means for estimating the input signal ( 12 ′) is a further adaptive filter ( 20 ).

14. The hearing device of claim 13 , characterized in that the input signal ( 12 ) is operationally connected to the further adaptive filter ( 20 ).

15. The hearing device of claim 11 , characterized by further comprising means for subtracting the estimated input signal ( 14 ) weighted by a first factor (k 1 ) from the result of subtracting the estimated feedback signal ( 22 ) from the output signal ( 12 ) of the microphone ( 1 ), the first factor (k 1 ) having a value between 0 and 1, preferably a value of 0.9.

16. The hearing device of claim 11 , characterized by further comprising means for subtracting the estimated input signal ( 14 ) or a processed estimated input signal ( 14 ) from the output signal ( 13 ), the estimated input signal ( 14 ) or the processed estimated input signal ( 14 ) being weighted by a second factor (k 2 ) that has a value between 0 and 1, preferably a value of 0.1.

17. The hearing device of claim 15 , characterized in that the estimated input signal ( 14 ) is fed to the transfer function unit ( 2 ′) for processing the estimated input signal ( 14 ).

18. The method of claim 8 , characterized by involving the transfer function ( 2 ) in the processing of the estimated input signal ( 14 ).

19. The hearing device of claim 16 , characterized in that the estimated input signal ( 14 ) is fed to the transfer function unit ( 2 ′) for processing the estimated input signal ( 14 ).