ACTIVE NOISE REDUCTION ADAPTIVE FILTER ADAPTATION RATE ADJUSTING

• US 20100098265A1
• Filed: 10/20/2008
• Published: 04/22/2010
• Est. Priority Date: 10/20/2008
• Status: Active Grant

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Cheng, Christopher J., Pan, Davis Y.
• Granted Patent: US 8,306,240 B2
• Time in Patent Office: Days
• US Class Current: 381/94.1
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• 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: G10K 2210/128 Vehicles
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

A method for determining leakage factors or adaptation rates, or both, for adaptive filters in an active noise reduction system. The leakage factor or adaptation rate, or both, may vary depending on a parameter of an input reference signal. The parameter may include one or more of reference signal input frequency, rate of change of reference input signal frequency, if a predetermined triggering condition exits, or if a predetermined event has occurred.

Claims

1. A method, comprising:

determining an adaptation rate for use in an adaptive filter of a noise reduction system based on a frequency-related parameter of the reference input signal;

applying the adaptation rate to coefficients of the adaptive filter; and

applying the coefficients to an audio signal.

2. A method according to claim 1, wherein the parameter is the frequency of the reference input signal.

3. A method according to claim 1, wherein the parameter is the rate of change of the frequency of the reference input signal.

4. A method according to claim 1, wherein the determining comprises selecting the adaptation rate from a plurality of predetermined adaptations rates.

5. A method according to claim 1, wherein the determining comprises calculating the adaptation rate.

6. A method according to claim 1, further comprising:

determining leakage factors; and

applying the leakage factors to the filter coefficients.

7. A method according to claim 6, further comprising smoothing the leakage factors.

8. A method according to claim 6, wherein the determining the leakage factors comprises determining the leakage factors as a function of a parameter of the reference input signal.

9. An active noise reduction system comprising;

circuitry for determining an adaptation rate for use in an adaptive filter of a noise reduction system as a function of a frequency-related parameter of a reference input signal;

circuitry for applying the adaptation rate to coefficients of the adaptive filter; and

circuitry for applying the coefficient to an audio signal.

10. An active noise reduction system according to claim 9, wherein the parameter is the frequency of a reference input signal

11. An active noise reduction system according to claim 9, wherein the parameter is the rate of change of the frequency of the input reference signal.

12. An active noise reduction system according to claim 9 wherein at least one of the circuitry for determining, the circuitry for applying the adaptation rate, or the circuitry for applying the coefficient is implemented as a set of instruction for execution by a digital signal processing element.

13. An active noise reduction system according to claim 9, wherein the circuitry for determining comprises circuitry for selecting the adaptation rate from a plurality of predetermined adaptation rate values.

14. An active noise reduction system according to claim 9, wherein the circuitry for determining comprises circuitry for calculating the adaptation rate.

15. An active noise reduction system according to claim 9, further comprising a leakage adjuster to provide leakage factors to apply to the filter coefficients.

16. An active noise reduction system according to claim 15, further comprising a data smoother to provide smoothed leakage factors to apply to the filter coefficients.

17. An active noise reduction system according to claim 15, the leakage adjuster comprising circuitry to determine the leakage factor as a function of a parameter of the reference input signal.

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

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

determining adaptation rates associated with the filter coefficients;

applying the filter coefficients to an audio signal;

wherein the determining comprises

in response to a first triggering condition, providing a first adaptation rate;

in response to a second triggering condition, providing a second adaptation rate, different from the first adaptation rate; and

in the absence of the first triggering condition and the second triggering condition, providing a default adaptation rate; and

wherein at least one of the providing the first adaptation rate, providing the second adaptation rate, and providing the third adaptation rate comprises providing an adaptation rate value determined as a function of a frequency-related parameter of a reference input signal.

19. A method in accordance with claim 18, further comprising:

determining a leakage factor for use in the adaptive filter based on a parameter of the reference input signal; and

applying the leakage factor to the coefficients of the adaptive filter.