Systems and methods for adapting estimated secondary path

1. A noise-cancellation system with secondary path adaptation, comprising:

a noise-cancellation filter configured to receive a reference signal representative of a source of noise within a predefined volume and generating, based at least in part on the reference signal, a noise-cancellation signal that, when transduced by a speaker, produces a noise-cancellation acoustic signal that reduces noise in a cancellation zone within the predefined volume;

a secondary path estimation filter configured to receive an input signal and to implement an estimate of secondary path transfer function, the secondary path transfer function being a transfer function between the speaker and a cancellation zone, the secondary path estimation filter outputting an output signal based, at least in part, on the estimate of the secondary path transfer function and the input signal;

an adaptive module configured to adjust coefficients of the noise-cancellation filter according to a first adaptive algorithm, based, at least in part, on the estimated output signal; and

an secondary path adaptive module configured to adjust coefficients of the secondary path estimation filter according to a second adaptive algorithm, wherein a rate of adaptation of the second adaptive algorithm is based, at least in part, on a coherence between the reference signal and an error signal representative of residual noise within the cancellation zone.

2. The noise-cancellation system of claim 1 , wherein the input signal is the error signal, wherein the output signal is an estimated error that is phase-shifted with respect to the error signal to remove a delay between the speaker and the cancellation zone, wherein the delay is determined according to the estimate of the secondary path transfer function.

3. The noise-cancellation system of claim 1 , wherein the input signal is the reference signal, wherein the output signal is an estimated reference signal that is phase-shifted with respect to the error signal to introduce a delay between the speaker and the cancellation zone, the delay being estimated according to the estimate of the secondary path transfer function.

4. The noise-cancellation system of claim 1 , wherein the rate of adaptation is monotonically related to the coherence between the reference signal and the error signal.

5. The noise-cancellation system of claim 1 , wherein the coherence between the reference signal and the error signal is determined by a coherence between the noise-cancellation signal and the error signal or by a coherence between the error signal and an estimate of the noise-cancellation signal at the cancellation zone, the estimate of the noise-cancellation signal at the cancellation zone being determined according to the estimate of the secondary path transfer function.

6. The noise-cancellation system of claim 1 , wherein the error signal comprises the output of a projection filter receiving an input from an error sensor disposed at a position outside the cancellation zone and configured to estimate the residual noise within the cancellation zone.

7. The noise-cancellation system of claim 1 , wherein the first adaptive algorithm and the second adaptive algorithm are each least mean squares algorithms.

8. The noise-cancellation system of claim 1 , wherein the error signal comprises the output of an echo canceler receiving an input from an error sensor and cancelling a component of the input attributable to the output of the speaker or at least a second speaker in the predefined volume.

9. The noise-cancellation system of claim 1 , further comprising an echo canceler receiving a program content signal, the program content signal being transduced by the speaker into a program content acoustic signal, the echo canceler comprising an echo canceler filter implementing the estimate of the secondary path transfer function such that the echo canceler filter outputs an estimated program content signal that estimates the program content signal acoustic signal at the cancellation zone, the estimated program content signal being subtracted from an input received from an error sensor to cancel a component of the input attributable to the program content acoustic signal.

10. A non-transitory storage medium comprising program code that, when executed by a processor, implements the steps of:

receiving a reference signal representative of a source of noise within a predefined volume and generating with a noise-cancellation filter, based at least in part on the reference signal, a noise-cancellation signal that, when transduced by a speaker, produces a noise-cancellation acoustic signal that reduces noise in a cancellation zone within the predefined volume;

outputting, with a secondary path estimation filter, an estimated output according to an estimate of a secondary path transfer function, the secondary path transfer function being a transfer function between the speaker and a cancellation zone, and an input signal;

adjusting coefficients of the noise-cancellation filter according to a first adaptive algorithm, based, at least in part, on the estimated output signal; and

adjusting coefficients of the secondary path estimation filter according to a second adaptive algorithm, wherein a rate of adaptation of the second adaptive algorithm is based, at least in part, on a coherence between the reference signal and an error signal representative of residual noise within the cancellation zone.

11. The non-transitory storage medium of claim 10 , wherein the input signal is the error signal, wherein the output signal is an estimated error that is phase-shifted with respect to the error signal to remove a delay between the speaker and the cancellation zone, wherein the delay is determined according to the estimate of the secondary path transfer function.

12. The non-transitory storage medium of claim 10 , wherein the input signal is the reference signal, wherein the output signal is an estimated reference signal that is phase-shifted with respect to the error signal to introduce a delay between the speaker and the cancellation zone, the delay being estimated according to the estimate of the secondary path transfer function.

13. The non-transitory storage medium of claim 10 , the rate of adaptation is monotonically related to the coherence between the reference signal and the error signal.

14. The non-transitory storage medium of claim 10 , wherein the coherence between the reference signal and the error signal is determined by a coherence between the noise-cancellation signal and the error signal or by a coherence between the error signal and an estimate of the noise-cancellation signal at the cancellation zone, the estimate of the noise-cancellation signal at the cancellation zone being determined according to the estimate of the secondary path transfer function.

15. The non-transitory storage medium of claim 10 , wherein the error signal comprises the output of a projection filter receiving an input from an error sensor disposed at a position outside the cancellation zone and configured to estimate the residual noise within the cancellation zone.

16. The non-transitory storage medium of claim 10 , wherein the first adaptive algorithm and the second adaptive algorithm are least means squares algorithms.

17. A noise-cancellation system with secondary path adaptation, comprising:

a noise-cancellation filter configured to receive a reference signal representative of a source of noise within a predefined volume and generating, based at least in part on the reference signal, a noise-cancellation signal that, when transduced by a speaker, produces a noise-cancellation acoustic signal that reduces noise in a cancellation zone within the predefined volume;

a secondary path estimation filter configured to calculate an estimate of secondary path transfer function, the secondary path transfer function being a transfer function between the speaker and a cancellation zone,

an secondary path adaptive module configured to adjust coefficients of the secondary path estimation filter according to a second adaptive algorithm, wherein a rate of adaptation of the second adaptive algorithm is based, at least in part, on a coherence between the reference signal and an error signal representative of residual noise within the cancellation zone, and

an echo canceler receiving a program content signal, the program content signal being transduced by the speaker into a program content acoustic signal, the echo canceler comprising an echo canceler filter implementing the estimate of the secondary path transfer function such that the echo canceler filter outputs an estimated program content signal that estimates the program content signal acoustic signal at the cancellation zone, the estimated program content signal being subtracted from the error signal to cancel a component of the input attributable to the program content acoustic signal.

18. The noise-cancellation system of claim 17 , wherein the rate of adaptation is monotonically related to the coherence between the reference signal and the error signal.

19. The noise-cancellation system of claim 17 , wherein the coherence between the reference signal and the error signal is determined by a coherence between the noise-cancellation signal and the error signal or by a coherence between the error signal and an estimate of the noise-cancellation signal at the cancellation zone, the estimate of the noise-cancellation signal at the cancellation zone being determined according to the estimate of the secondary path transfer function.

20. The noise-cancellation system of claim 17 , wherein the error signal comprises the output of a projection filter receiving an input from an error sensor disposed at a position outside the cancellation zone and configured to estimate the residual noise within the cancellation zone.