Systems, methods, apparatus, and computer-readable media for adaptive active noise cancellation

1. An apparatus for active noise cancellation, said apparatus comprising:

a reference microphone configured to produce a reference microphone signal in response to a first acoustic signal;

a first analog-to-digital converter (ADC) that is coupled to the reference microphone and configured to produce an output signal that is based on the reference microphone signal;

an error microphone configured to produce an error microphone signal in response to a second acoustic signal;

a second ADC that is coupled to the error microphone and configured to produce an output signal that is based on the error microphone signal;

a processor (A) having a first input coupled to the first ADC, a second input coupled to the second ADC, and a third input configured to receive a desired sound signal at a first sampling rate and (B) configured to provide updates based on the first, second, and third inputs; and

a digital filter that is coupled to the first ADC, arranged to receive the updates from the processor, and configured to filter a reference noise signal that is based on the output signal of the first ADC, at a second sampling rate that is higher than the first sampling rate, to produce an anti-noise signal.

2. The apparatus according to claim 1 , wherein at least one among said first ADC and said second ADC includes a sigma-delta modulator.

3. The apparatus according to claim 1 , wherein said apparatus includes:

a mixer that is coupled to the digital filter and configured to produce an output signal that is based on the anti-noise signal and on the desired sound signal, and

a loudspeaker that is coupled to the mixer and arranged to produce an acoustic signal that is based on the output signal of the mixer.

4. The apparatus according to claim 3 , wherein said error microphone is arranged to be disposed within an acoustic field generated by the loudspeaker.

5. The apparatus according to claim 3 , wherein said apparatus includes a codec configured to produce a far-end communications signal, and

wherein said processor is coupled to said codec and configured to receive, as said desired sound signal, a signal based on the far-end communications signal, and

wherein said digital filter includes a path estimate filter configured to estimate a path that includes an acoustic path between the loudspeaker and the error microphone, and

wherein said path estimate filter is configured to filter the desired sound signal at the second sampling rate, and

wherein said second input of the processor is coupled to an output of the path estimate filter.

6. The apparatus according to claim 5 , wherein said first input is coupled to the first ADC via a first decimator and said second input is coupled to said output of the path estimate filter via a second decimator.

7. The apparatus according to claim 5 , wherein the first input is coupled to the first ADC via a copy of the path estimate filter.

8. The apparatus according to claim 3 , wherein said mixer is configured to mix the anti-noise signal and the desired sound signal to produce said output signal of the mixer, and

wherein said apparatus includes:

a codec configured to produce a far-end communications signal;

a voice microphone configured to produce a voice signal in response to a voice of a user of the apparatus; and

a second mixer coupled to said codec and said voice microphone and configured to produce the desired sound signal based on the far-end communications signal and on the voice signal.

9. The apparatus according to claim 1 , wherein said apparatus includes a codec configured to produce a far-end communications signal, and

wherein said processor is coupled to said codec and configured to receive, as said desired sound signal, a signal based on the far-end communications signal.

10. The apparatus according to claim 1 , wherein said desired sound signal includes a multimedia signal.

11. The apparatus according to claim 1 , wherein said apparatus includes a voice microphone configured to produce a voice signal in response to a voice of a user of the apparatus, and

wherein said processor is coupled to said voice microphone and configured to receive, as said desired sound signal, a sidetone signal that is based on said voice signal.

12. The apparatus according to claim 1 , wherein said apparatus includes:

a second reference microphone configured to produce a second reference microphone signal in response to a corresponding acoustic signal;

a third ADC that is coupled to the second reference microphone and configured to produce an output signal that is based on the second reference microphone signal; and

a spatially selective filter coupled to the first ADC and to the third ADC and configured to perform a spatially selective processing operation to produce the reference noise signal.

13. A method for active noise cancellation, said method comprising:

applying a digital filter to a reference noise signal at a first sampling rate to produce an anti-noise signal; and

during said applying the digital filter, updating the digital filter based on a first input signal at a second sampling rate that is lower than the first sampling rate, a second input signal at the second sampling rate, and a third input signal at the second sampling rate,

wherein the reference noise signal is based on a signal produced by a reference microphone, and

wherein the first input signal is based on first information from a desired sound signal, and

wherein the second input signal is based on second information from the desired sound signal and on information from a signal produced by an error microphone, and

wherein the third input signal is based on information from the signal produced by the reference microphone.

14. The method according to claim 13 , wherein method comprises using sigma-delta modulation to produce the reference noise signal.

15. The method according to claim 13 , wherein said method includes driving a loudspeaker to produce an acoustic signal that is based on the anti-noise signal and on the desired sound signal.

16. The method according to claim 15 , wherein said error microphone is disposed within an acoustic field generated by the loudspeaker.

17. The method according to claim 15 , wherein said method includes producing a far-end communications signal based on received data, and

wherein said desired sound signal is based on the far-end communications signal, and

wherein said method includes applying a path estimate filter to the desired sound signal at the first sampling rate to produce a filtered desired sound signal,

wherein said path estimate filter estimates a path that includes an acoustic path between the loudspeaker and the error microphone, and

wherein said second information from the desired sound signal is from the filtered desired sound signal.

18. The method according to claim 17 , wherein said method comprises applying a copy of the path estimate filter to a signal that is based on the signal produced by the reference microphone, and

wherein the third input signal is based on an output of said copy of the path estimate filter.

19. The method according to claim 15 , wherein said method includes mixing the anti-noise signal and the desired sound signal to produce a mixed signal for driving the loudspeaker, and

wherein said method includes:

producing a far-end communications signal based on received data;

producing a digital voice signal in response to an acoustic voice signal; and

mixing a signal based on the far-end communications signal with a signal based on the digital voice signal to produce the desired sound signal.

20. The method according to claim 13 , wherein said method includes producing a far-end communications signal based on received data, and

wherein said desired sound signal is based on the far-end communications signal.

21. The method according to claim 13 , wherein said method includes decoding a stored file to produce a multimedia signal, and

wherein said desired sound signal is based on the multimedia signal.

22. The method according to claim 13 , wherein said method includes producing a digital voice signal in response to an acoustic voice signal sensed by a voice microphone of a device that also includes the reference microphone, and

wherein said desired sound signal is a sidetone signal that is based on said digital voice signal.

23. The method according to claim 13 , wherein said method includes performing a spatially selective processing operation on at least (A) the signal produced by the reference microphone and (B) a signal produced by a second reference microphone to produce a spatially processed signal,

wherein the reference noise signal is based on the spatially processed signal.