Active Noise Reduction Adaptive Filter Leakage Adjusting

• US 20090220102A1
• Filed: 02/29/2008
• Published: 09/03/2009
• Est. Priority Date: 02/29/2008
• Status: Active Grant

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Pan, Davis Y., Cheng, Christopher J., Salvador, Eduardo T.
• Granted Patent: US 8,204,242 B2
• Time in Patent Office: Days
• US Class Current: 381/71.110
• 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

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;

wherein the determining comprises calculating a leakage factor as a function of the magnitude of a cancellation signal that is output by the adaptive filter.

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

3. 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;

wherein the applying comprises multiplying an old filter coefficient value and a filter coefficient update amount by the smoothed leakage factors.

4. 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, the leakage adjuster comprising circuitry to calculate leakage factors as a function of the magnitude of the output of the active noise reduction signal and to provide the leakage factors to the data smoother.

5. An active noise reduction system according to claim 4, wherein the coefficient calculator comprises circuitry to apply the smoothed leakage factors to an old filter coefficient value and to a filter coefficient update amount to provide a new filter coefficient value.

6. 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;

wherein the coefficient calculator comprises circuitry to apply the smoothed leakage factors to an old filter coefficient value and to a filter coefficient update amount to provide a new filter coefficient value.

7. 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

wherein at least one of the providing the first leakage factor, providing the second leakage factor, and providing the third leakage factor comprises providing a calculated leakage factor value calculated as a function of the magnitude of a cancellation signal that is output by the active noise reduction system.

8. A method comprising:

applying, by a signal processor, a leakage factor to an adaptive filter coefficient value and to a coefficient value update amount to provide an updated adaptive coefficient value; and

applying the updated adaptive coefficient value to an audio signal.

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

10. A method in accordance with claim 9, wherein the method is incorporated in the operation of an active noise reduction system in a vehicle.

11. A method in accordance with claim 8, 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.

12. A method in accordance with claim 8, 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.

13. A method comprising:

calculating a leakage factor for use in an adaptive filter of a noise reduction system as a function of the magnitude of the output of the adaptive filter;

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

applying the coefficients to an audio signal.

14. A method in accordance with claim 13, further comprising applying the leakage factor to a filter coefficient update amount.

15. A method in accordance with claim 13, wherein the method is incorporated in the operation of an active noise reduction system.

16. A method in accordance with claim 15, wherein the method is incorporated in the operation of an active noise reduction system in a vehicle

17. A method in accordance with claim 13, 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.

18. A method in accordance with claim 13, 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.