Entrainment resistant feedback cancellation

Abstract

This invention concerns a method, and a device, for feedback cancellation. This invention also concerns a computer program product comprising computer program code means to make a computer execute a procedure for feedback cancellation. The method comprises providing an adaptive feedback cancellation filter which adapts under the control of a control module, and filtering at least one input of the control module to suppress correlated signals from the input prior to the control module operating upon the input. The device comprises an adaptive feedback cancellation filter, a control module and at least one filter. The control module controls adaptation of the adaptive feedback cancellation filter. The filter suppresses correlated signals from an input to the control module prior to the control module operating upon the input.

The invention claimed is: 
     
       1. A method for feedback cancellation, the method comprising:
 providing an adaptive feedback cancellation filter which adapts under the control of a control module, wherein the control module provides updated filter taps for the adaptive feedback cancellation filter, and wherein the adaptive feedback cancellation filter produces a feedback cancellation signal; 
 filtering at least one input signal of the control module with a whitening filter to whiten the spectrum of the input signal to minimize variation in signal level across a frequency spectrum of the input signal and to produce a whitened input signal, prior to the control module operating upon the whitened input signal to generate the updated filter taps; and 
 partially whitening a forward path in respect of which the feedback cancellation is applied, with a partial whitening filter. 
 
     
     
       2. The method of  claim 1 , further comprising copying settings of the whitening filter to the partial whitening filter. 
     
     
       3. The method of  claim 1 , further comprising whitening at least two inputs of the control module by the whitening filter and the partial whitening filter, respectively; and minimizing signal path differences to the whitening filter and the partial whitening filter, by at least one delay. 
     
     
       4. The method of  claim 1  further comprising the adaptive feedback cancellation filter operating upon an un-whitened output signal to produce an un-whitened cancellation signal to be subtracted from an un-whitened input signal. 
     
     
       5. The method of  claim 4  wherein an error signal input to the control module is derived by:
 providing an offline filter having an identical response to the feedback cancellation filter; 
 inputting to the offline filter a whitened output signal; and 
 subtracting an output of the offline filter from a whitened input signal to obtain the error signal. 
 
     
     
       6. The method of  claim 1  further comprising whitening at least two inputs of the control module by the whitening filter and the partial whitening filter, respectively, wherein the whitening filter and the partial whitening filter have the same tap values. 
     
     
       7. The method of  claim 6  further comprising updating the tap values of the whitening filters only at regular intervals. 
     
     
       8. The method of  claim 1  wherein the feedback cancellation filter and one or more of the whitening filter and the partial whitening filter have the same number of filter taps and the same frequency resolution. 
     
     
       9. A device for feedback cancellation, the device comprising:
 an adaptive feedback cancellation filter; 
 a control module configured to control adaptation of the adaptive feedback cancellation filter by providing updated filter taps for the adaptive feedback cancellation filter; and 
 at least one whitening filter configured to whiten the spectrum of a signal input to the control module, to minimize variation in signal level across a frequency spectrum of the signal to produce a whitened input signal, prior to the control module operating upon the whitened input signal to generate the updated filter taps, and 
 a partial whitening filter for partially whitening a forward path in respect of which the feedback cancellation is applied. 
 
     
     
       10. The device of  claim 9  wherein settings of the whitening filter are copied to the partial whitening filter. 
     
     
       11. The device of  claim 9  wherein at least two inputs of the control module are whitened by the whitening filter and the partial whitening filter, respectively, and further comprising at least one delay to minimise signal path differences to the whitening filter and the partial whitening filter. 
     
     
       12. The device of  claim 9  wherein the adaptive feedback cancellation filter operates upon an un-whitened output signal to produce an un-whitened cancellation signal to be subtracted from an un-whitened input signal. 
     
     
       13. The device of  claim 9  further comprising an offline filter having an identical response to the feedback cancellation filter to derive an error signal input to the control module by inputting to the offline filter a whitened output signal, and subtracting an output of the offline filter from a whitened input signal to obtain the error signal. 
     
     
       14. The device of  claim 9  wherein the feedback cancellation filter and one or more of the whitening filter and the partial whitening filter have the same number of filter taps and the same frequency resolution. 
     
     
       15. A computer program product comprising a computer-readable, tangible storage device having a non-transitory computer-readable program code stored therein, said computer-readable program code containing instructions to make a computer execute a procedure for feedback cancellation, the computer program product comprising:
 computer-readable program code for providing a control module which controls an adaptive feedback cancellation filter, wherein the control module provides updated filter taps for the adaptive feedback cancellation filter, and wherein the adaptive feedback cancellation filter produces a feedback cancellation signal; 
 computer-readable program code for filtering at least one input of the control module with a whitening filter to whiten the spectrum of a signal at the input, to minimize variation in signal level across a frequency spectrum of the signal to produce a whitened input signal, prior to the control module operating upon the whitened input signal to generate the updated filter taps; and 
 computer-readable program code for partially whitening a forward path in respect of which the feedback cancellation signal is applied, with a partial whitening filter.