Active Noise Reduction Adaptive Filter Leakage Adjusting

• US 20080095383A1
• Filed: 06/26/2006
• Published: 04/24/2008
• Est. Priority Date: 06/26/2006
• Status: Active Grant

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Salvador, Eduardo, Pan, Davis, Cheng, Christopher J.
• Granted Patent: US 8,194,873 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17883 the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• 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: H03H 21/0067 Means or methods for compensation of undesirable effects

Abstract

An active noise reduction system using adaptive filters. A method of operation the active noise reduction system includes smoothing a stream of leakage factors. The frequency of a noise reduction signal may be related to the engine speed of an engine associated with the system within which the active noise reduction system is operated. The engine speed signal may be a high latency signal and may be obtained by the active noise reduction system over audio entertainment circuitry.

Claims

1. A method for operating an active noise reduction system comprising:

providing filter coefficients for an adaptive filter in response to a noise signal;

determining leakage factors;

smoothing the leakage factors to provide smoothed leakage factors; and

applying the smoothed leakage factors to the filter coefficients to provide modified filter coefficients.

2. A method in accordance with claim 1, further comprising:

responsive to the modified filter coefficients, providing an active noise reduction signal characterized by a magnitude.

3. A method in accordance with claim 2, further comprising combining the active noise reduction signal with an audio entertainment signal.

4. A method in accordance with claim 3, wherein the audio entertainment signal is associated with a vehicle audio system.

5. A method in accordance with claim 1, wherein the determining is responsive to a triggering condition.

6. A method in accordance with claim 5, wherein the triggering condition comprises the result of comparing the magnitude of the active noise reduction signal in a first spectral band with a first threshold.

7. A method in accordance with claim 6 wherein the triggering condition comprises the result of comparing the magnitude of the active noise reduction signal in a second spectral band with a second threshold.

8. A method in accordance with claim 7 wherein the second threshold has a predetermined relationship to the first threshold.

9. A method in accordance with claim 6, wherein the first threshold is related to causing a device to operate non-linearly.

10. A method in accordance with claim 5, wherein the triggering condition comprises the result of monitoring the active noise reduction system to determine if a predefined event has occurred.

11. A method in accordance with claim 10 wherein the predefined event is that an entertainment signal magnitude is within a predetermined range of a magnitude that causes a device to operate non-linearly.

12. A method in accordance with claim 10 wherein the predefined event occurs in an audio entertainment system.

13. A method in accordance with claim 12, wherein the audio entertainment system is associated with a vehicle.

14. A method in accordance with claim 10, wherein the predefined event is the deactivation of the active noise reduction system.

15. A method in accordance with claim 10, wherein the predefined event is that a noise signal is above a threshold associated with non-linear operation of an input transducer.

16. A method in accordance with claim 1, wherein the smoothing comprises low pass filtering.

17. A method in accordance with claim 1, wherein prior to the smoothing, the determining comprises selecting one of a discrete number of predetermined values for the leakage factor.

18. A method in accordance with claim 17, wherein the discrete number is two.

19. A method in accordance with claim 17, wherein the discrete number is greater than two.

20. A method in accordance with claim 1, wherein the noise reduction system is configured to be installed in a vehicle.

21. A method in accordance with claim 1, wherein the determining is responsive to a plurality of triggering conditions.

22. A method in accordance with claim 21, wherein the leakage factor determining comprises

determining which of the plurality of triggering conditions exist;

responsive to a determining that a first triggering condition exists, selecting a first leakage factor value; and

responsive to a determining that a second triggering condition exists, selecting a second leakage factor value.

23. An active noise reduction system comprising:

an adaptive filter, for providing an active noise reduction signal;

a coefficient calculator, for providing filter coefficients for the adaptive filter; and

a leakage adjuster comprising a data smoother to provide smoothed leakage factors to apply to the filter coefficients.

24. Apparatus in accordance with claim 23, further comprising:

circuitry for comparing the active noise reduction signal magnitude to a threshold.

25. Apparatus in accordance with claim 24, further comprising:

monitoring circuitry for monitoring the active noise reduction system to determine if a predefined event has occurred, wherein the leakage adjuster is responsive to the monitoring circuitry.

26. Apparatus in accordance with claim 25, further comprising an audio entertainment system wherein the monitoring circuitry comprises circuitry for monitoring the audio entertainment system to determine if an entertainment audio signal magnitude is within a predetermined range of a magnitude that causes a device to operate non-linearly.

27. Apparatus in accordance with claim 25, wherein the monitoring circuitry comprises circuitry for determining if the active noise reduction system has been deactivated.

28. Apparatus in accordance with claim 25, further comprising an input transducer for transducing periodic vibrational energy to a noise signal, wherein the monitoring circuitry comprises circuitry for determining if the magnitude of the noise signal is above a threshold associated with non-linear operation of the input transducer.

29. Apparatus in accordance with claim 23, wherein the data smoother comprises a low pass filter.

30. Apparatus in accordance with claim 23, wherein the leakage adjuster is constructed and arranged to select one of a discrete number of values for the leakage factor.

31. Apparatus in accordance with claim 23 further comprising:

an audio entertainment system for providing an audio entertainment audio signal; and

a combiner for combining the noise reduction signal.

32. A method for operating an noise reduction system comprising:

providing a stream of leakage factor values; and

smoothing the stream of leakage factor values to provide a smoothed stream of leakage factor values.

33. A method in accordance with claim 32, wherein the value of each of the stream of leakage valued is selected from a discrete number of predefined values.

34. A method in accordance with claim 32, wherein the providing of each of the stream of leakage values in responsive to a detectible condition of the active noise reduction system.

35. A method in accordance with claim 34, wherein the detectible condition is that the active noise reduction system has been deactivated.

36. A method in accordance with claim 34, wherein the detectible condition is that the active noise reduction system has generated an audio signal having a magnitude greater than a threshold magnitude.

37. A method in accordance with claim 34, wherein the detectible condition is that the magnitude of a noise signal is above a threshold associated with non-linear operation of an input transducer.

38. A method in accordance with claim 32, wherein the providing of each of the stream of leakage values comprises selecting a leakage factor value from a plurality of predetermined leakage factor values.

39. A method in accordance with claim 32, further comprising

applying the smoothed stream of leakage factor values to coefficients of an adaptive filter of an active noise reduction system.

40. A method for operating an adaptive filter of an active noise reduction system, the adaptive filter characterized by coefficients, the method comprising:

smoothing the steam of leakage factor values to provide smoothed leakage factor values; and

applying the smoothed leakage factor values to the coefficients to provide modified coefficient values.

41. A method in accordance with claim 40, wherein the stream of leakage factor values comprises values selected from a discrete number of predetermined leakage factor values.

42. A method in accordance with claim 41, wherein the discrete number is two.

43. A method in accordance with claim 40, wherein the providing the stream of leakage factors comprises calculating leakage factor values.

44. A method for operating an active noise reduction system comprising:

providing a first threshold amplitude for a noise reduction signal corresponding to a first noise amplitude limit for a first frequency;

providing a second threshold amplitude for noise reduction signal corresponding to a second noise amplitude limit for a second frequency, wherein the second noise amplitude limit has a predetermined relationship to the first noise amplitude limit;

calculating filter coefficients associated with adaptive filters associated with the noise reduction system to provide a noise reduction signal characterized by a magnitude; and

determining, responsive to a comparing of the magnitude of the noise reduction signal to the first threshold amplitude at the first frequency and to the second threshold amplitude of the second frequency, leakage factors of modifying the filter coefficients.

45. A method in accordance with claim 44, herein the second frequency is a predetermined multiple of the first frequency.

46. A method in accordance with claim 45, wherein the second noise amplitude limit is non-zero.

47. A method in accordance with claim 45, wherein the active noise reduction system is associated with sinusoidal noise source and wherein the first frequency is related to the frequency of the sinusoidal noise source.

48. A method in accordance with claim 47, wherein the sinusoidal noise source is an engine.

49. A method in accordance with claim 48, wherein the engine is associated with a vehicle.

50. A method in accordance with claim 44, wherein the active noise reduction system is associated with a sinusoidal noise source and wherein the first frequency is related to the frequency of the sinusoidal noise source.

51. A method for operating an active noise reduction system, comprising:

determining an amplitude of a first noise reduction signal characterized by a first frequency; and

providing a non-zero noise reduction amplitude limit for a second frequency, wherein the second frequency has a predetermined relationship to the first frequency and wherein the noise reduction amplitude limit has a predetermined relationship to the first amplitude.

52. A method in accordance with claim 51, further comprising

in response to a noise signal characterized by the second frequency and by an amplitude, providing filter coefficients of an adaptive filter to reduce the noise signal amplitude;

in the event that the noise signal amplitude is greater than the noise reduction amplitude limit, applying a first leakage factor to the filter coefficients; and

in the event that the noise signal amplitude is equal to or greater than the noise reduction amplitude limit, applying a second leakage factor to the filter coefficients.

54. A method in accordance with claim 51, wherein the active noise reduction system is associated with a sinusoidal noise source and wherein the first frequency is related to the frequency of the sinusoidal noise source.

55. A method in accordance with claim 54, wherein the sinusoidal noise source is an engine.

56. A method in accordance with claim 55, wherein the engine is associated with a vehicle.

57. A method in accordance with claim 51, further comprising nulling the first noise reduction signal.

58. A method for operating an active noise reduction system comprising:

providing filter coefficients of an adaptive filter in response to a noise signal;

determining leakage factors associated with the filter coefficients, wherein the determining comprises

in response to a first triggering condition, providing a first leakage factor;

in response to a second triggering condition, providing a second leakage factor, different from the first leakage factor; and

in the absence of the first triggering condition and the second triggering condition, providing a default leakage factor.