ADAPTIVE ACTIVE NOISE CANCELING FOR HANDSET

• US 20120316872A1
• Filed: 06/07/2011
• Published: 12/13/2012
• Est. Priority Date: 06/07/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Adams, Robert, Stoltz, Thomas, Spetzler Berthelsen, Kim
• Granted Patent: US 8,909,524 B2
• Time in Patent Office: Days
• US Class Current: 704/233
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise

Abstract

Embodiments of the present invention provide an adaptive noise canceling system. The adaptive noise canceling system may be used in a handset to cancel background noise by generating an anti-noise signal. The adaptive noise canceling system may include first input to receive a first signal from a feedforward microphone; a second input to receive a second signal from an error microphone; a controller coupled to the inputs, the controller configured to adaptively generate an anti-noise signal according to the received signals, wherein the controller derives a profile of the anti-noise signal from the first signal and derives a magnitude of the anti-noise signal from both first and second signal; and an output to transmit the anti-noise signal to a speaker.

Claims

1. A system, comprising:

a first input to receive a first signal from a feedforward microphone;

a second input to receive a second signal from an error microphone;

a controller coupled to the inputs, the controller configured to adaptively generate an anti-noise signal according to the received signals, wherein the controller derives a profile of the anti-noise signal from the first signal and adjusts a magnitude of the anti-noise signal based on both first and second signals; and

an output to transmit the anti-noise signal to a speaker.

2. The system of claim 1, wherein the anti-noise signal is 180°

out of phase with background noise.

3. The system of claim 1, wherein the second signal is an error signal between background noise, the anti-noise signal, and a downlink signal.

4. The system of claim 1, wherein the system is provided on an integrated circuit.

5. The system of claim 1, the controller comprises a filter block.

6. The system of claim 5, wherein the filter block executes an adaptive least mean squared (LMS) algorithm where an error signal is measured and is the second signal.

7. The system of claim 6, wherein a LMS coefficient is calculated by the filter block according to the equation:

G₁=G₀+μ

*F*E,

G₁ is the LMS coefficient, G₀ is the previous LMS coefficient, μ

is a weighting coefficient, F is the first signal, and E is the error signal.

8. The system of claim 1, further comprises a speech detector, coupled to the controller, to detect speech in a downlink channel and the controller further configured to suspend adaptive generation of the anti-noise signal while still providing the anti-noise signal at the output during detected periods of speech in the downlink channel.

9. The system of claim 8, wherein the speech detector comprises a root mean square (RMS) level estimator and a noise floor estimator to determine whether speech detected is above a minimum threshold.

10. The system of claim 8, wherein the speech detector comprises a proximity detector.

11. The system of claim 1, further comprises a wind detector coupled to the feedforward input and error input, and configured to adjust adaptive generation of the anti-noise signal by the controller during wind detected periods.

12. The system of claim 11, wherein the controller suspends adaptive generation of the anti-noise signal while still providing the anti-noise signal at the output during wind detected periods.

13. The system of claim 11, wherein the controller suspends adaptive generation of the active noise signal and does not provide any anti-noise signal at the output during wind detected periods.

14. The system of claim 11, wherein the controller suspends adaptive generation of the active noise signal and fades out providing the anti-noise signal at the output during wind detected periods.

15. The system of claim 14, wherein the anti-noise signal is faded out according to the wind'"'"'s magnitude.

16. The system of claim 11, wherein the wind detector comprises:

an energy detector receiving the second signal and generating an energy threshold output;

a correlation estimator receiving the first and second signals, generating a correlation estimate of the two signals; and

a wind controller receiving the correlation estimate and energy threshold output and generating a wind control signal to be outputted to the controller.

17. The system of claim 16, wherein the wind detector further comprises a low pass filter.

18. The system of claim 17, wherein the high pass filter filters signals below 500 Hz.

19. The system of claim 1, further comprises a noise floor detector coupled to the first input to detect a noise level, wherein the controller halts anti-noise signal output if noise is below a minimum noise level threshold.

20. The system of claim 1, further comprises a noise floor detector coupled to the first input to detect a noise level, wherein the controller halts anti-noise signal output if noise is above a maximum noise level threshold.

21. The system of claim 1, further comprises a limiter to attenuate the first signal to keep the first signal below a limiting threshold.

22. A method, comprising:

receiving a feedforward input from a first microphone;

receiving an error input from a second microphone;

calculating a background noise signal based on the feedforward input and the error input;

adaptively generating an anti-noise signal that is 180°

out of phase with the background noise signal; and

outputting the anti-noise signal to a speaker.

23. The method claim 22, wherein the anti-noise signal is generated using an adaptive LMS algorithm with a measured error signal.

24. The system of claim 23, wherein a LMS coefficient is calculated by the filter block according to the equation:

G₁=G₀+μ

*F*E,

G₁ is the LMS coefficient, G₀ is the previous LMS coefficient, μ

is a weighting coefficient, F is the feedforward signal, and E is the error signal.

25. The method claim 22, further comprises:

detecting speech in a downlink signal; and

suspending adaptive generation of the anti-noise signal while still outputting the anti-noise signal during detected speech periods.

26. The method claim 22, further comprises:

detecting wind based on the feedforward input and error input; and

adjusting the adaptive generation of the anti-noise signal during detected wind periods.

27. The method of claim 26, wherein suspending adaptive generation of the anti-noise signal while still outputting the anti-noise signal during detected wind periods.

28. The method of claim 26, wherein suspending adaptive generation of the anti-noise signal and suspending outputting the anti-noise signal during detected wind periods.

29. The method of claim 26, wherein suspending adaptive generation of the anti-noise signal and fading out outputting the anti-noise signal during detected wind periods.

30. The method of claim 29, wherein the anti-noise signal is faded out according to the wind'"'"'s magnitude.

31. The method of claim 26, wherein the wind is detected by generating a correlation estimate between the feedforward input and error input.

32. The method of claim 31, further comprises filtering the feedforward input and error input before generating the correlation estimate.

33. The method claim 22, further comprises:

measuring a noise level in the feedforward input; and

suspending anti-noise signal generation and output if the noise level is below a minimum threshold.

34. The method claim 22, further comprises:

measuring a noise level in the feedforward input; and

suspending anti-noise signal generation and output if the noise level is above a maximum threshold.

35. The method claim 22, further comprises:

attenuating the feedforward input to keep the feedforward input below a limiting threshold.

36. A handset, comprising:

a speaker;

a feedforward microphone;

an error microphone, wherein the error microphone is located closer to the speaker than the feedforward microphone; and

an adaptive noise control system, coupled to the feedforward and error microphone, to generate an anti-noise signal based on background noise captured from the feedforward microphone and an error signal captured from the error microphone, and to output the anti-noise signal to the speaker.

37. The handset of claim 36, wherein the adaptive noise control system is an integrated circuit.

38. The handset of claim 36, further comprises:

an equalizer coupled to the feedforward microphone and adaptive noise control system.

39. The handset of claim 36, further comprises:

an antenna to receive a downlink signal; and

an adder to combine the downlink signal and anti-noise signal.