ACTIVE NOISE REDUCTION ADAPTIVE FILTER LEAKAGE ADJUSTING

• US 20100098263A1
• 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: Salvador, Eduardo T., Pan, Davis Y.
• Granted Patent: US 8,355,512 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17835 using detection of abnormal input signals
• 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 2210/1282 Automobiles
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3056 Variable gain

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 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;

applying the smoothed leakage factors to the filter coefficients to provide modified filter coefficients; and

applying the filter coefficients to an audio signal.

wherein the determining comprises determining a leakage factor as a function of the frequency of an input reference signal.

2. A method in accordance with claim 1, wherein the applying comprises multiplying an old filter coefficient value and a filter coefficient update amount by the smoothed leakage factors.

3. 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;

a leakage adjuster comprising a data smoother to provide smoothed leakage factors to apply to the filter coefficients, and further comprising circuitry to determine leakage factors as a function of the frequency of an input reference signal and to provide the leakage factors to the data smoother; and

circuitry for applying the coefficients to an audio signal.

4. 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; and

applying the filter coefficients to an audio signal;

wherein at least one of the providing the first leakage factor, providing the second leakage factor, and providing the third leakage factor determining the leakage factor value as a function of the frequency of a reference input signal.

5. A method comprising:

determining a leakage factor for use in an adaptive filter of a noise reduction system as a function of the frequency of an input reference signal;

applying the leakage factor to coefficients of the adaptive filter; and

applying the coefficients to an audio signal.

6. A method in accordance with claim 5, further comprising applying the leakage factor to a filter coefficient update amount.

7. A method in accordance with claim 5, wherein the method is incorporated in the operation of an active noise reduction system.

8. A method in accordance with claim 7, wherein the method is incorporated in the operation of an active noise reduction system in a vehicle.

9. A method in accordance with claim 5, wherein the applying the leakage factor comprises combining the adaptive filter coefficient value and the coefficient value update amount prior to the applying the leakage factor.

10. A method in accordance with claim 5, wherein the applying the leakage factor comprises:

applying the leakage factor to the adaptive filter coefficient value to provide a modified adaptive filter coefficient value;

applying the leakage factor to the coefficient value update amount to provide a modified coefficient value update amount; and

combining the modified adaptive filter coefficient value and the modified coefficient value update amount.