Power management of adaptive noise cancellation (ANC) in a personal audio device

• US 9,230,532 B1
• Filed: 03/12/2013
• Issued: 01/05/2016
• Est. Priority Date: 09/14/2012
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Lu, Yang, Zhou, Dayong, Hendrix, Jon D., Alderson, Jeffrey
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Suthers, Douglas
• Application Number:
  US13/794,931
• Time in Patent Office: 1,029 Days
• Field of Search: 381/71.2, 381/71.1, 381/71.11, 381/71.12
• US Class Current: 1/1
• CPC Class Codes: G10K 11/16 Methods or devices for protecting against, or for damping, noise or other acoustic waves in general G10K11/36 takes precedence
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/1783 handling or detecting of non-standard events or conditions, e.g. changing operating modes under specific operating conditions
• 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 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 2410/05 Noise reduction with a separate noise microphone
• CPC Class Codes: H04R 2460/01 Hearing devices using active noise cancellation
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from an output of a microphone that measures ambient audio. The anti-noise signal is combined with source audio to provide an output for a speaker. The anti-noise signal causes cancellation of ambient audio sounds that appear at the microphone. A processing circuit estimates a level of background noise from the microphone output and sets a power conservation mode of the personal audio device in response to detecting that the background noise level is lower than a predetermined threshold.

Claims

1. A personal audio device, comprising:

a personal audio device housing;

a transducer mounted on the housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

at least one microphone mounted on the housing for providing at least one microphone signal indicative of the ambient audio sounds; and

a processing circuit that generates the anti-noise signal using an adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with the at least one microphone signal, and wherein the processing circuit further estimates a background noise level from the at least one microphone signal and sets a power conservation mode of the personal audio device in conformity with a magnitude of the estimated background noise level, wherein the processing circuit estimates the background noise level from a minimum value of noise sources within a time interval having a predetermined duration using a noise power measurement algorithm that measures the at least one microphone signal using a minima-tracking algorithm over the time interval to filter non-stationary noise sources and non-noise sources from the at least one microphone signal.

2. The personal audio device of claim 1, wherein the processing circuit further sets a full power mode of the personal audio device in response to detecting that the background noise level is greater than a predetermined threshold.

3. The personal audio device of claim 2, wherein the processing circuit further sets a lower-power operating mode of the personal audio device in response to detecting that the background noise level is less than a second value, wherein the second value is greater than the predetermined threshold by a difference in the range of 3 decibels to 10 decibels.

4. The personal audio device of claim 1, wherein the predetermined duration is adjustable to vary a property of the non-stationary noise sources filtered from the at least one microphone signal.

5. The personal audio device of claim 1, wherein the processing circuit filters the minimum value of the noise sources provided by the noise power measurement algorithm with a smoothing function to control a rate of change of the estimate of the background noise level used to detect whether or not to set the power conservation mode.

6. The personal audio device of claim 5, wherein the processing circuit implements a scratch or wind noise detection algorithm, and wherein the processing circuit adjusts the smoothing function to reduce the rate of change of the smoothing function in response to detecting scratch or wind noise, whereby the estimate of the background noise remains accurate in the presence of scratch or wind noise.

7. The personal audio device of claim 5, wherein the processing circuit implements a near speech detection algorithm, and wherein the processing circuit adjusts the smoothing function to reduce the rate of change of the smoothing function in response to detecting of near speech, whereby the estimate of the background noise remains accurate in the presence of near speech.

8. The personal audio device of claim 5, wherein the smoothing function is an exponential smoothing function.

9. The personal audio device of claim 1, wherein the processing circuit compares the background noise level to multiple thresholds and sets one of multiple power conservation modes of the personal audio device in response to a result of the comparisons.

10. A method of countering effects of ambient audio sounds by a personal audio device, the method comprising:

adaptively generating an anti-noise signal using an adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with the at least one microphone signal;

combining the anti-noise signal with source audio;

providing a result of the combining to a transducer;

measuring the ambient audio sounds with at least one microphone;

estimating a background noise level from a minimum value of noise sources within a time interval having a predetermined duration by measuring the at least one microphone signal using a minima-tracking algorithm over the time interval to filter non-stationary noise sources and non-noise sources from the at least one microphone signal; and

setting a power conservation mode of the personal audio device in conformity with a magnitude of the estimated background noise level.

11. The method of claim 10, wherein the setting a power conservation mode further comprises:

detecting that the background noise level is greater than a predetermined threshold; and

setting a full power mode of the personal audio device in response to detecting that the background noise level is greater than the predetermined threshold.

12. The method of claim 11, wherein the setting a power conservation mode further sets a lower-power operating mode of the personal audio device in response to detecting that the background noise level is less than a second value, wherein the second value is greater than the predetermined threshold by a difference in the range of 3 decibels to 10 decibels.

13. The method of claim 10, wherein the estimating further comprises adjusting the predetermined duration to vary a property of the non-stationary noise sources filtered from the at least one microphone signal.

14. The method of claim 10, wherein the estimating further comprises filtering the minimum value of the noise sources provided by the noise power measurement algorithm with a smoothing function to control a rate of change of the estimate of the background noise level used to detect whether or not to set the power conservation mode.

15. The method of claim 14, further comprising:

detecting scratch or wind noise detection; and

adjusting the smoothing function to reduce the rate of change of the smoothing function in response to the detecting scratch or wind noise, whereby the estimate of the background noise remains accurate in the presence of scratch or wind noise.

16. The method of claim 14, further comprising:

detecting near speech; and

adjusting the smoothing function to reduce the rate of change of the smoothing function in response to detecting near speech, whereby the estimate of the background noise remains accurate in the presence of near speech.

17. The method of claim 14, wherein the smoothing function is an exponential smoothing function.

18. The method of claim 10, further comprising comparing the background noise level to multiple thresholds, and wherein the setting sets one of multiple power conservation modes of the personal audio device in response to a result of the comparing.

19. An integrated circuit for implementing at least a portion of a personal audio device, comprising:

an output for providing an output signal to an output transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

at least one microphone input for receiving at least one microphone signal indicative of the ambient audio sounds; and

a processing circuit that adaptively generates the anti-noise signal using an adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with the at least one microphone signal, and wherein the processing circuit further estimates a background noise level from the at least one microphone signal and sets a power conservation mode of the personal audio device in conformity with a magnitude of the estimated background noise level, wherein the processing circuit estimates the background noise level from a minimum value of noise sources within a time interval having a predetermined duration using a noise power measurement algorithm that measures the at least one microphone signal using a minima-tracking algorithm over the time interval to filter non-stationary noise sources and non-noise sources from the at least one microphone signal.

20. The integrated circuit of claim 19, wherein the the processing circuit further sets a full power mode of the personal audio device in response to detecting that the background noise level is greater than a predetermined threshold.

21. The integrated circuit of claim 20, wherein the processing circuit further sets a lower-power operating mode of the personal audio device in response to detecting that the background noise level is less than a second value, wherein the second value is greater than the predetermined threshold by a difference in the range of 3 decibels to 10 decibels.

22. The integrated circuit of claim 19, wherein the predetermined duration is adjustable to vary a property of the non-stationary noise sources filtered from the at least one microphone signal.

23. The integrated circuit of claim 19, wherein the processing circuit filters the minimum value of the noise sources provided by the noise power measurement algorithm with a smoothing function to control a rate of change of the estimate of the background noise level used to detect whether or not to set the power conservation mode.

24. The integrated circuit of claim 23, wherein the processing circuit implements a scratch or wind noise detection algorithm, and wherein the processing circuit adjusts the smoothing function to reduce the rate of change of the smoothing function in response to detecting scratch or wind noise, whereby the estimate of the background noise remains accurate in the presence of scratch or wind noise.

25. The integrated circuit of claim 23, wherein the processing circuit implements a near speech detection algorithm, and wherein the processing circuit adjusts the smoothing function to reduce the rate of change of the smoothing function in response to detecting of near speech, whereby the estimate of the background noise remains accurate in the presence of near speech.

26. The integrated circuit of claim 23, wherein the smoothing function is an exponential smoothing function.

27. The integrated circuit of claim 19, wherein the processing circuit compares the background noise level to multiple threshold and sets one of multiple power conservation modes of the personal audio device in response to a result of the comparisons.