FILTER ARCHITECTURE FOR AN ADAPTIVE NOISE CANCELER IN A PERSONAL AUDIO DEVICE

• US 20120308026A1
• Filed: 03/30/2012
• Published: 12/06/2012
• Est. Priority Date: 06/03/2011
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Kamath, Gautham Devendra, Hendrix, Jon D.
• Granted Patent: US 9,076,431 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: G10K 2210/3017 Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/30391 Resetting of the filter parameters or changing the algorithm according to prevailing conditions
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe

Abstract

A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cancel ambient audio sounds. A processing circuit implements one or more adaptive filters that control the generation of the anti-noise signal. At least one of the adaptive filters is partitioned into a first portion having a fixed frequency response and a second portion having a variable frequency response. The partitioned filter may be an adaptive filter that generates the anti-noise signal directly from the reference microphone signal. An error microphone may be provided to measure the ambient sounds and transducer output near the transducer, and a secondary path adaptive filter included to generate an error signal from the error microphone signal, which may be partitioned, alone or in combination.

Claims

1. A personal audio device, comprising:

a personal audio device housing;

a transducer mounted on the housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

a reference microphone mounted on the housing for providing a reference microphone signal indicative of the ambient audio sounds; and

a processing circuit that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a partitioned filter that controls the generation of the anti-noise signal, wherein the filter is partitioned into a first filter portion having a fixed frequency response that is combined with a variable frequency response of a second filter portion, wherein the processing circuit shapes the spectrum of the anti-noise signal in conformity with the reference microphone signal to minimize the ambient audio sounds heard by the listener.

2. The personal audio device of claim 1, wherein the partitioned filter receives the reference microphone signal and generates the anti-noise signal by filtering the reference microphone signal.

3. The personal audio device of claim 1, further comprising an error microphone mounted on the housing in proximity to the transducer for providing an error microphone signal indicative of the acoustic output of the transducer and the ambient audio sounds at the transducer, and wherein the processing circuit implements an adaptive filter that generates the anti-noise signal in conformity with the error microphone signal and the reference microphone signal by adapting the variable frequency response of the second filter portion to minimize the ambient audio sounds at the error microphone, and wherein the partitioned filter is a secondary path filter having a secondary path response that shapes the source audio and a combiner that removes the source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit adapts the variable response of the second filter to minimize components of the error signal that are correlated with an output of another filter that applies a copy of the secondary path response to the reference microphone signal.

4. The personal audio device of claim 3, wherein the processing circuit further implements a third filter that receives the reference microphone signal and generates the anti-noise signal by filtering the reference microphone signal, wherein the third filter is partitioned into a third filter portion having another fixed frequency response that is combined with another variable frequency response of a fourth filter portion.

5. The personal audio device of claim 1, wherein the first filter portion and the second filter portion are coupled in parallel.

6. The personal audio device of claim 1, wherein the first filter portion and the second filter portion are coupled in series.

7. The personal audio device of claim 1, wherein an adaptive control of the variable frequency response of the second filter portion has a leakage characteristic that restores the response of the partitioned filter to a predetermined response at a particular rate of change.

8. The personal audio device of claim 7, wherein the leakage characteristic restores the response of the partitioned filter to the fixed frequency response of the first filter portion .

9. The personal audio device of claim 1, wherein the fixed frequency response of the first filter portion is selectable from among multiple predetermined frequency responses.

10. The personal audio device of claim 9, wherein at least one of the multiple predetermined frequency responses is an historic frequency response of the partitioned filter representing a combination of the fixed frequency response of the first filter portion and a historic frequency response of the second filter portion, wherein the processing circuit selects the at least one of the multiple predetermined frequency responses to initialize the combined response of the partitioned filter to a previously adapted-to state.

11. The personal audio device of claim 9, wherein the processing circuit selects the fixed frequency response of the first filter in conformity with a heuristic or a detected environmental condition.

12. The personal audio device of claim 1, wherein an initial value of the variable frequency response of the second filter portion is selectable from among multiple predetermined frequency responses.

13. The personal audio device of claim 12, wherein at least one of the multiple predetermined frequency responses is an historic frequency response of the second filter portion, wherein the processing circuit selects the at least one of the multiple predetermined frequency responses to initialize the variable frequency response of the second filter portion to a previously adapted-to state.

14. The personal audio device of claim 12, wherein the processing circuit selects the initial value of the variable frequency response of the second filter portion in conformity with a heuristic or a detected environmental condition.

15. A method of canceling ambient audio sounds in the proximity of a transducer of a personal audio device, the method comprising:

first measuring ambient audio sounds with a reference microphone to produce a reference microphone signal;

adaptively generating an anti-noise signal for countering the effects of ambient audio sounds at an acoustic output of the transducer, to shape the spectrum of the anti-noise signal in conformity with the reference microphone signal to minimize the ambient audio sounds heard by the listener, wherein the adaptively generating controls the generation of the anti-noise signal using a combined response of a first fixed filter response and a second variable filter response; and

combining the anti-noise signal with a source audio signal to generate an audio signal provided to the transducer.

16. The method of claim 15, wherein the first fixed filter response and the second fixed filter response receive the reference microphone signal and generate the anti-noise signal by filtering the reference microphone signal.

17. The method of claim 15, further comprising second measuring an output of the transducer and the ambient audio sounds at the transducer with an error microphone to produce an error microphone signal, wherein the adaptively generating adjusts the second variable filter response in conformity with the error microphone signal and the reference microphone signal by adapting the variable response to minimize the ambient audio sounds at the error microphone, and wherein the combined response of the first fixed filter response and the second adaptive filter response implements a secondary path response that shapes the source audio to generate shaped source audio, and wherein the method further comprises:

removing the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener; and

filtering the reference microphone signal with a copy of the secondary path response to generate a shaped reference microphone signal, and wherein the adaptively generating adjusts the second variable filter response to minimize components of the error signal that are correlated with the shaped reference microphone signal.

18. The method of claim 17, wherein the adaptively generating generates the anti-noise signal by:

first filtering the reference microphone signal with a third fixed filter response;

second filtering the reference microphone signal with a fourth variable filter response; and

combining a result of the first filtering and a result of the second filtering to generate the anti-noise signal, wherein the adaptively generating further adjusts the fourth variable filter response to minimize the ambient audio sounds at the error microphone.

19. The method of claim 15, wherein the adaptively generating comprises combining an output of the first fixed filter response and an output of the second variable filter response to yield a combined output.

20. The method of claim 15, wherein the adaptively generating comprises cascading the first fixed filter response and the second variable filter response to yield a combined output.

21. The method of claim 15, wherein the adaptively generating controls the variable response of the second filter portion with a leakage characteristic that restores the response of the partitioned filter to a predetermined response at a particular rate of change.

22. The method of claim 21, wherein the leakage characteristic restores the response of the partitioned filter to the first fixed filter response.

23. The method of claim 15, further comprising selecting the first fixed filter response from among multiple predetermined frequency responses.

24. The method of claim 23, wherein at least one of the multiple predetermined frequency responses is an historic frequency response of the partitioned filter representing a combination of the first fixed filter response and an historic of the second variable filter response, wherein the selecting selects the at least one of the multiple predetermined frequency responses to initialize a frequency response of the combined filter response to a previously adapted-to state.

25. The method of claim 23, wherein the processing circuit selects the fixed frequency response of the first filter in conformity with a heuristic or a detected environmental condition.

26. The method of claim 15, further comprising selecting an initial value of the second variable filter response from among multiple predetermined frequency responses.

27. The method of claim 26, wherein at least one of the multiple predetermined frequency responses is an historic value of the second variable filter response, wherein the selecting selects the at least one of the multiple predetermined frequency responses to initialize the second variable filter response to a previously adapted-to state.

28. The method of claim 26, wherein the selecting selects the initial value of the second variable filter response in conformity with a heuristic or a detected environmental condition.

29. An integrated circuit for implementing at least a portion of a personal audio device, comprising:

an output for providing a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

a reference microphone input for receiving a reference microphone signal indicative of the ambient audio sounds; and

a processing circuit that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a partitioned filter that controls the generation of the anti-noise signal, wherein the filter is partitioned into a first filter portion having a fixed frequency response that is combined with a variable frequency response of a second filter portion, wherein the processing circuit shapes the spectrum of the anti-noise signal in conformity with the reference microphone signal to minimize the ambient audio sounds heard by the listener.

30. The integrated circuit of claim 29, wherein the partitioned filter receives the reference microphone signal and generates the anti-noise signal by filtering the reference microphone signal.

31. The integrated circuit of claim 29, further comprising an error microphone input for receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer, and wherein the processing circuit implements an adaptive filter that generates the anti-noise signal in conformity with the error microphone signal and the reference microphone signal by adapting the variable frequency response of the second filter portion to minimize the ambient audio sounds at the error microphone, and wherein the partitioned filter is a secondary path filter having a secondary path response that shapes the source audio and a combiner that removes the source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit adapts the variable response of the second filter to minimize components of the error signal that are correlated with an output of another filter that applies a copy of the secondary path response to the reference microphone signal.

32. The integrated circuit of claim 31, wherein the processing circuit further implements a third filter that receives the reference microphone signal and generates the anti-noise signal by filtering the reference microphone signal , wherein the third filter is partitioned into a third filter portion having another fixed frequency response that is combined with another variable frequency response of a fourth filter portion.

33. The integrated circuit of claim 29, wherein the first filter portion and the second filter portion are coupled in parallel.

34. The integrated circuit of claim 29, wherein the first filter portion and the second filter portion are coupled in series.

35. The integrated circuit of claim 29, wherein an adaptive control of the variable frequency response of the second filter portion has a leakage characteristic that restores the response of the partitioned filter to a predetermined response at a particular rate of change.

36. The integrated circuit of claim 35, wherein the leakage characteristic restores the response of the partitioned filter to the fixed frequency response of the first filter portion.

37. The integrated circuit of claim 29, wherein the fixed frequency response of the first filter portion is selectable from among multiple predetermined frequency responses.

38. The integrated circuit of claim 37, wherein at least one of the multiple predetermined frequency responses is an historic frequency response of the partitioned filter representing a combination of the fixed frequency response of the first filter portion and a historic frequency response of the second filter portion, wherein the processing circuit selects the at least one of the multiple predetermined frequency responses to initialize the combined response of the partitioned filter to a previously adapted-to state.

39. The integrated circuit of claim 37, wherein the processing circuit selects the fixed frequency response of the first filter in conformity with a heuristic or a detected environmental condition.

40. The integrated circuit of claim 29, wherein an initial value of the variable frequency response of the second filter portion is selectable from among multiple predetermined frequency responses.

41. The integrated circuit of claim 40, wherein at least one of the multiple predetermined frequency responses is an historic frequency response of the second filter portion, wherein the processing circuit selects the at least one of the multiple predetermined frequency responses to initialize the variable frequency response of the second filter portion to a previously adapted-to state.

42. The integrated circuit of claim 40, wherein the processing circuit selects the initial value of the variable frequency response of the second filter portion in conformity with a heuristic or a detected environmental condition.