ADAPTIVE NOISE CONTROL SYSTEM

• US 20100014685A1
• Filed: 06/12/2009
• Published: 01/21/2010
• Est. Priority Date: 06/13/2008
• Status: Active Grant

• Current Assignee: Harman Becker Automotive Systems GmbH (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman Becker Automotive Systems GmbH (Samsung Electronics Co. Ltd.)
• Inventors: Wurm, Michael
• Granted Patent: US 8,565,443 B2
• Time in Patent Office: Days
• US Class Current: 381/71.110
• CPC Class Codes: G10K 11/17815 between the reference signals and the error signals, i.e. primary path
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• 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 11/17833 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 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• 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 2210/3022 Error paths
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters

Abstract

An active noise cancellation system that reduces, at a listening position, power of a noise signal radiated from a noise source to the listening position. The system includes an adaptive filter, at least one acoustic actuator and a signal processing device. The adaptive filter receives a reference signal representing the noise signal, and provides a compensation signal. The at least one acoustic actuator radiates the compensation signal to the listening position. The signal processing device evaluates and assesses the stability of the adaptive filter.

Claims

1. An active noise cancellation system for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the system comprising:

an adaptive filter that receives a reference signal representing the noise signal and provides a compensation signal;

at least one acoustic actuator that receives the compensation signal and radiates an audio compensation signal indicative of the compensation signal to the listening position; and

a signal processing device that evaluates and assesses the stability of the adaptive filter.

2. The system of claim 1, further comprising an LMS adaptation unit to adjust filter characteristics of the adaptive filter using a least mean square algorithm, where the LMS algorithm has a step-size parameter and a leakage parameter.

3. The system of claim 2, where the least mean square algorithm is one of a filtered-x-LMS algorithm and a modified filtered-x-LMS algorithm.

4. The system of claim 2, further comprising a microphone disposed at the listening position, where the microphone senses and provides a residual error signal.

5. The system of claim 4, further comprising a filter connected downstream to the adaptive filter to provide an estimation of the compensation signal at the listening position.

6. The system of claim 5, further comprising a subtractor that subtracts the estimated compensation signal at the listening position from the error signal and provides an estimated noise signal at the listening position.

7. The system of claim 6, where the signal processing device further comprises signal processing units configured to, respectively, receive the error signal, the estimated compensation signal at the listening position, and the estimated noise signal at the listening position, where each signal processing unit is configured to calculate at least one signal parameter of its respective input signal.

8. The system of claim 7, where the signal parameter is indicative of signal power.

9. The system of claim 8, where the signal processing device further comprises a decider unit connected downstream to the signal processing units, where the decider unit evaluates the signal parameters for assessing the stability of the adaptive filter.

10. The system of claim 9, where the decider unit assesses the adaptive filter as stable, and if the ratio between the signal power of the estimated compensation signal at the listening position and the signal power of the estimated noise signal at the listening position is below a given threshold.

11. The system of claim 9, where the decider unit assesses the adaptive filter as stable, and if the ratio between the power of the residual error signal and the power of the estimated noise signal at the listening position is within a given interval.

12. The system of claim 9, where the decider unit deactivates the active noise control system if the adaptive filter is assessed as unstable.

13. The system of claim 9, where the decider unit modifies at least one of the step size parameter and the leakage parameter where the adaptive filter is assessed as unstable.

14. The system of claim 9, where the decider unit provides a signal indicating whether the adaptive filter is assessed as unstable.

15. The system of claim 9, where the decider unit initiates a re-initialization of the system parameter where the adaptive filter is assessed as unstable.

16. The system of claim 12, where the decider unit deactivates the active noise control system where the adaptive filter is assessed as unstable for longer than a pre-defined period.

17. The system of one claim 9, where the signal processing device evaluates and assesses the stability of the adaptive filter separately at different frequencies, which different frequencies include a base frequency and higher order harmonics thereof.

19. The system of claim 1, further comprising a secondary path estimation system that estimates a transfer function describing transfer characteristics between the acoustic actuator and the microphone.

20. The system of claim 17, further comprising

a non-acoustical sensor that provides information about a base frequency of the noise signal;

and

an oscillator that provides the reference signal;

where the reference signal is composed of harmonic oscillations with the base frequency and higher order harmonics thereof.

21. The system of claim 1, further comprising an acoustic sensor that provides the reference signal, where the reference signal is a broad band signal.

22. The system of claim 1, further comprising

a non-acoustical sensor that provides information about a base frequency of the noise signal;

an oscillator that provides a first reference signal, wherein the first reference signal includes harmonic oscillations having at least one of a base frequency and higher order harmonics thereof;

an acoustic sensor that provides a second reference signal, wherein the second reference signal is a broad band signal; and

a superposition device that superposes the first and the second reference signal, and provides the superposition as a third reference signal.

18. The system of claim 18, where the adaptive filter multiplies each frequency component of the input signal with a complex filter coefficient.

23. An active noise cancellation system for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the system comprising:

a filter arrangement including a first adaptive filter and an equalization filter, the filter arrangement receives an effective reference signal representing the noise signal and provides a compensation signal, where a transfer characteristic of the equalization filter is characterized by a first transfer function; and

at least one acoustic actuator that radiates the compensation signal to the listening position, which signal path between the acoustic actuator and the listening position is characterized by a secondary path transfer function;

where the product of the first transfer function and the secondary path transfer function matches a given target function.

24. The system of claim 23, where the target function or the magnitude of the target function equals one in a given frequency range.

25. The system of claim 23, further comprising

a first sensor that provides a first reference signal;

and

means for providing a second reference signal that is correlated to the first reference signal, where the effective reference signal is a function of the first and the second reference signal.

26. The system of claim 25, further comprising a superposition system that superposes the first reference signal and the second reference signal, and provides the effective reference signal.

27. The system of claim 25, where the means for providing a second reference signal comprises:

a non-acoustical sensor configured to provide an output signal representing a base frequency of the second reference signal; and

an oscillator configured to provide, as a second reference signal, a harmonic oscillation of the base frequency and higher harmonics thereof.

28. The system of one of claims 23, further comprising a secondary path estimation system that estimates a secondary path transfer function.

29. The system of claim 28, where the secondary path estimation system further comprises a second adaptive filter.

30. The system of claim 28, further comprising an extractor connected to the secondary path estimation system to provide filter coefficients for the equalization filter.

31. The system of claim 23, further comprising:

an adaptation unit connected to the first adaptive filter to provide filter coefficients thereto; and

a band-pass filter configured in at least one signal path connected to the adaptation unit, where the band-pass filter provides at least one pass-band having a center frequency equal to at least one of a fundamental frequency and at least one higher harmonic thereof.

32. The system of claim 23, further comprising

a signal processing device that evaluates and assesses the stability of the first adaptive filter.

33. An active noise cancellation method for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the method comprising:

providing a reference signal correlated with the noise signal;

filtering the reference signal with an adaptive filter to provide a compensation signal;

radiating the compensation signal to the listening position;

sensing a residual error signal at the listening position;

adapting filter coefficients of the adaptive filter as a function of the error signal and the reference signal; and

evaluating and assessing the stability of the adaptive filter.

34. The method of claim 33, further comprising:

estimating the compensation signal and the noise signal at the listening position; and

where the evaluating and assessing step comprises

determining the power of the estimated compensation signal, the estimated noise signal, and the residual error signal;

calculating stability parameters from the signal power values; and

comparing the stability parameters with given threshold values to evaluate stability of the adaptive filter.

35. The method of claim 33, further comprising filtering the compensation signal with a compensation filter before radiating the compensation signal with an acoustic actuator, where the compensation filter includes a transfer characteristic chosen such that the total transfer characteristic characterizing a signal path from the acoustic actuator to the listening position is equalized.

36. An active noise cancellation method for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the method comprising:

providing a reference signal correlated with the noise signal;

sequentially filtering the reference signal with an adaptive filter and an equalization filter to provide a compensation signal, where a transfer characteristic of the equalization filter is characterized by a first transfer function;

radiating the compensation signal to the listening position with an acoustic actuator, where a signal path from the acoustic actuator to the listening position is characterized by a secondary path transfer function, and where the product of the first transfer function and the secondary path transfer function matches a given target function;

sensing a residual error signal at the listening position; and

adapting filter coefficients of the adaptive filter as a function of the error signal and the reference signal.

37. The method of claim 36, further comprising

providing a base frequency with a non-acoustical sensor;

and

oscillating an oscillator on at least one of the base frequency and at least one higher harmonic thereof to provide the reference signal.

38. The method of claim 37, where the secondary path transfer function and the first transfer function of the equalization filter are represented by a complex coefficient for each considered frequency, the base frequency and the at least one higher harmonic, and where the complex coefficients representing the first transfer function are complex inverses of the respective complex coefficients representing the secondary path transfer function.