In-vehicle noise cancellation adaptive filter divergence control
View Patent ↗A active noise cancellation (ANC) system may include an adaptive filter divergence detector for detecting divergence of the one or more controllable filters as they adapt, based on various temporal or frequency domain amplitude characteristics. Upon detection of a controllable filter divergence, the ANC system may be deactivated, or certain speakers may be muted. Alternatively, the ANC system may modify the diverged controllable filters to restore proper operation of the noise cancelling system. This may include adjusting a leakage value of an adaptive filter controller.
1. A method for controlling stability in an active noise cancellation (ANC) system, the method comprising:
receiving, from an adaptive filter controller, filter coefficients corresponding to at least one controllable filter;
computing a parameter based on an analysis of at least a portion of the filter coefficients;
detecting divergence of the at least one controllable filter based on a comparison of the parameter to a threshold, wherein the threshold is a dynamic threshold computed from a statistical analysis of the parameter computed from filter coefficients in one or more preceding adaptations of the at least one controllable filter; and
modifying properties of the at least one controllable filter that has diverged.
2. The method of claim 1 , wherein the controllable filter includes a plurality of coefficients, the parameter being a sum of absolute values of at least a portion of the coefficients in the at least one controllable filter.
3. The method of claim 1 , wherein the controllable filter includes a plurality of coefficients, the parameter being a maximum value of at least a portion of the coefficients in the at least one controllable filter.
4. The method of claim 1 , wherein detecting divergence of the at least one controllable filter based on a comparison of the parameter to a threshold comprises detecting divergence of the at least one controllable filter when the parameter exceeds the threshold.
5. The method of claim 1 , wherein the threshold is an average value of the parameter taken from multiple preceding adaptations of the at least one controllable filter multiplied by a gain factor.
6. The method of claim 1 , wherein modifying properties of the at least one controllable filter that has diverged comprises deactivating at least one of the ANC system and the at least one controllable filter that has diverged.
7. The method of claim 1 , wherein modifying properties of the at least one controllable filter that has diverged comprises resetting the filter coefficients of the at least one controllable filter to zero and allowing the at least one controllable filter to re-adapt.
8. The method of claim 1 , wherein modifying properties of the at least one controllable filter that has diverged comprises resetting the filter coefficients of the at least one controllable filter to a set of filter coefficient values stored in a memory of the ANC system.
9. The method of claim 1 , wherein modifying properties of the at least one controllable filter that has diverged comprises increasing a leakage value of the adaptive filter controller in response to detecting divergence of the at least one controllable filter.
10. The method of claim 9 , wherein the leakage value of the adaptive filter controller is increased at the diverged frequencies of the at least one controllable filter.
11. The method of claim 9 , further comprising:
decreasing the leakage value of the adaptive filter controller when a highest magnitude filter coefficient of the at least one controllable filter falls below a predetermined threshold.
12. An active noise cancellation (ANC) system comprising:
at least one controllable filter configured to generate an anti-noise signal based on an adaptive transfer characteristic and a noise signal received from a sensor, the adaptive transfer characteristic of the at least one controllable filter characterized by a set of filter coefficients;
an adaptive filter controller, including a processor and memory, programmed to adapt the set of filter coefficients based on the noise signal and an error signal received from a microphone located in a cabin of a vehicle; and
a divergence controller in communication with at least the adaptive filter controller, the divergence controller including a processor and memory programmed to:
receive the set of filter coefficients corresponding to a current adaptation of the adaptive transfer characteristic of the at least one controllable filter;
compute a parameter based on an analysis of at least a portion of the set of filter coefficients; and
detect divergence of the at least one controllable filter when a difference between the parameter computed from the current adaptation of the at least one controllable filter and an average value of the same parameter from one or more previous adaptations of the at least one controllable filter exceeds a threshold.
13. The ANC system of claim 12 , wherein the threshold is a predetermined static threshold programmed for the ANC system.
14. The ANC system of claim 12 , wherein the divergence controller is further programmed to increase a leakage value of the adaptive filter controller in response to detecting divergence of the at least one controllable filter.
15. A computer-program product embodied in a non-transitory computer readable medium that is programmed for active noise cancellation (ANC), the computer-program product comprising instructions for:
receiving, from an adaptive filter controller, a set of filter coefficients corresponding to a current adaptation of at least one controllable filter;
computing a parameter based on an analysis of at least a portion of the filter coefficients;
detecting divergence of the at least one controllable filter when a difference between the parameter computed from the current adaptation of the at least one controllable filter and an average value of the same parameter from one or more previous adaptations exceeds a threshold; and
modifying an adaptive transfer characteristic of the at least one controllable filter during the current adaptation in response to detecting divergence of the at least one controllable filter.
16. The computer-program product of claim 15 , wherein the instructions for detecting divergence of the at least one controllable filter includes detecting, in the time domain, diverged frequencies of the at least one controllable filter; and
wherein the instructions for modifying the adaptive transfer characteristic includes, in the time domain, resetting the diverged frequencies of the at least one controllable filter to zero, attenuating the filter coefficients at the diverged frequencies, or increasing a leakage value of the adaptive filter controller at the diverged frequencies.
17. The computer-program product of claim 15 , wherein the instructions for detecting divergence of the at least one controllable filter includes detecting, in the frequency domain, diverged frequencies of the at least one controllable filter; and
wherein the instructions for modifying the adaptive transfer characteristic includes, in the frequency domain, notching out the diverged frequencies using an error signal received from a microphone and filter coefficients from a previous adaptation of the at least one controllable filter stored in memory.