Active Noise Cancellation Using a Predictive Approach

• US 20090136052A1
• Filed: 11/27/2007
• Published: 05/28/2009
• Est. Priority Date: 11/27/2007
• Status: Abandoned Application

• Current Assignee: David Clark Company Incorporated
• Original Assignee: David Clark Company Incorporated
• Inventors: Hohlfeld, Robert G., Sheppard, Allan E. JR.
• Application Number:
  US11/945,494
• Publication Number:
  US 20090136052A1
• Time in Patent Office: Days
• US Class Current: 381/71.100
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• 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 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3023 Estimation of noise, e.g. on error signals
• CPC Class Codes: G10K 2210/3035 Models, e.g. of the acoustic system
• CPC Class Codes: G10K 2210/3047 Prediction, e.g. of future values of noise
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe

Abstract

A method for active noise cancellation in a volume generates a mathematical model of a noise process to be cancelled. Using the mathematical model, a noise signal in a next sample period is predicted from a measured noise signal. The predicted signal is inverted and applied to the volume. Destructive interference of the noise signal and the inverted signal cancels the noise in the volume.

Claims

1. A method of active noise cancellation in a volume comprising:

generating a mathematical model of a noise process to be cancelled;

constructing an extrapolated noise signal from the mathematical model;

inverting the extrapolated signal;

applying the inverted signal to the volume; and

canceling the noise in the volume using the applied signal.

2. The method of claim 1, further comprising:

measuring the noise signal close to the volume;

converting the noise signal to a digital signal; and

inputting the noise signal to the mathematical model.

3. The method of claim 1, further comprising, before applying the inverted signal to the volume, converting the inverted signal into an analog signal.

4. The method of claim 1, further comprising generating an anti-noise sound wave by a speaker operating within the volume.

5. The method of claim 4, wherein destructive interference of the noise signal and the anti-noise sound wave cancels the noise.

6. The method of claim 1, wherein the mathematical model is generated using at least one of linear predictive coding and maximum entropy method.

7. The method of claim 1, wherein the mathematical model is used to predict the noise signal in the next sample.

8. The method of claim 7, wherein the predicted signal for the next sample is used to cancel the noise signal in the next sample.

9. The method of claim 1, wherein the mathematical model is periodically updated.

10. The method of claim 1, wherein canceling the noise comprises canceling tonal and non-tonal noise components.

11. The method of claim 1, further comprising measuring the noise outside the volume.

12. The method of claim 1, further comprising measuring the noise outside the volume and measuring the noise within the volume.

13. The method of claim 1, wherein canceling the noise comprises canceling periodic noise and noise generated by turbulent air flow.

14. The method of claim 1, wherein the volume comprises at least one of a helmet, a headset, and speakers close to a head.

15. A method of active noise cancellation in a volume comprising:

measuring a noise signal;

predicting a noise signal in a next sample period from the measured noise signal;

inverting the predicted signal;

applying the inverted signal to the volume; and

canceling the noise signal in the next sample period using the predicted signal.

16. The method of claim 15, further comprising, prior to predicting the noise signal, converting the noise signal to a digital signal.

17. The method of claim 15, further comprising, before applying the inverted signal to the volume, converting the inverted signal into an analog signal.

18. The method of claim 15, further comprising generating an anti-noise sound wave by a speaker operating within the volume.

19. The method of claim 18, wherein destructive interference of the noise signal and the anti-noise sound wave cancels the noise.

20. The method of claim 15, wherein the predicted noise signal is generated using at least one of linear predictive coding and a maximum entropy method.

21. The method of claim 15, wherein canceling the noise signal comprises canceling tonal and non-tonal noise components.

22. The method of claim 15, further comprising measuring the noise outside the volume.

23. The method of claim 15, further comprising measuring the noise outside the volume and measuring the noise within the volume.

24. The method of claim 15, wherein canceling the noise signal comprises canceling periodic noise and noise generated by turbulent air flow.

25. The method of claim 15, wherein the volume comprises at least one of a helmet, a headset, and speakers close to a head.

26. An apparatus for active noise cancellation in a volume comprising:

a first microphone that senses noise;

a noise model generator that receives the sensed noise signal and generates a mathematical model of a noise process to be cancelled;

an extrapolator that extrapolates a noise signal from the mathematical model; and

an inverter that inverts the extrapolated signal and applies the signal to a volume.

27. The apparatus of claim 26, further comprising an analog-to-digital converter that receives the sensed noise signal from the first microphone and applies a digitized equivalent of an analog signal to the noise model generator.

28. The apparatus of claim 26, further comprising a digital-to-analog converter that receives the inverted signal from the inverter and applies an equivalent analog form of the digital signal to the volume.

29. The apparatus of claim 26, wherein the first microphone senses the noise outside the volume.

30. The apparatus of claim 26, further comprising a second microphone.

31. The apparatus of claim 30, wherein the second microphone senses the noise signal within the volume.

32. The apparatus of claim 26, wherein the noise model generator comprises at least one of a digital signal processor, a computer and a field-programmable gate array.

33. The apparatus of claim 26, wherein the noise model generator uses at least one of linear predictive coding and a maximum entropy method.

34. The apparatus of claim 26, wherein the noise model generator calculates an extrapolated value of the noise signal for a next sample period.

35. The apparatus of claim 26, wherein the extrapolator constructs the extrapolated noise signal for a future sample period.

36. The apparatus of claim 26, wherein the mathematical model is periodically updated.

37. The apparatus of claim 26, wherein the apparatus cancels tonal and non-tonal noise components.

38. The apparatus of claim 26, wherein the apparatus cancels periodic noise and noise generated by turbulent air flow.

39. The apparatus of claim 26, wherein the volume comprises at least one of a helmet, a headset, and speakers close to a head.

40. An apparatus for active noise cancellation in a volume comprising:

a first microphone that senses a noise signal;

a noise predictor that predicts a noise signal in a next sample period from the sensed noise signal;

an extrapolator that extrapolates a noise signal from the predicted noise signal; and

an inverter that inverts the extrapolated signal and applies the inverted signal to the volume.

41. The apparatus of claim 40, further comprising an analog-to-digital converter that receives the sensed noise signal from the first microphone and applies a digitized equivalent of an analog signal to the noise predictor.

42. The apparatus of claim 40, further comprising a digital-to-analog converter that receives the inverted signal from the inverter and applies an equivalent analog form of the digital signal to the volume.

43. The apparatus of claim 40, wherein the first microphone senses the noise outside the volume.

44. The apparatus of claim 40, further comprising a second microphone.

45. The apparatus of claim 44, wherein the second microphone senses the noise signal within the volume.

46. The apparatus of claim 40, wherein the noise predictor comprises at least one of a digital signal processor, a computer and a field-programmable gate array.

47. The apparatus of claim 40, wherein the noise predictor uses at least one of linear predictive coding and maximum entropy method.

48. The apparatus of claim 40, wherein the noise predictor calculates an extrapolated value of the noise signal for a next sample period.

49. The apparatus of claim 40, wherein the extrapolator constructs the extrapolated noise signal for a signal for a next sample period.

50. The apparatus of claim 40, wherein the predicted noise signal is periodically updated.

51. The apparatus of claim 40, wherein the apparatus cancels tonal and non-tonal noise components.

52. The apparatus of claim 40, wherein the apparatus cancels periodic noise and noise generated by turbulent air flow.

53. The apparatus of claim 40, wherein the volume comprises at least one of a helmet, a headset, and speakers close to a head.