SYSTEMS AND METHODS FOR ADAPTIVE NOISE CANCELLATION BY BIASING ANTI-NOISE LEVEL

• US 20140314244A1
• Filed: 07/16/2013
• Published: 10/23/2014
• Est. Priority Date: 04/17/2013
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Yong, Chin Huang, Alderson, Jeffrey D.
• Granted Patent: US 9,460,701 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• 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 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17827 Desired external signals, e.g. pass-through audio such as music or speech
• 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 11/17857 Geometric disposition, e.g. placement of microphones
• 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 2210/3014 Adaptive noise equalizers [ANE], i.e. where part of the unwanted sound is retained
• CPC Class Codes: G10K 2210/3017 Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
• CPC Class Codes: G10K 2210/3022 Error paths
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10K 2210/30351 Identification of the environment for applying appropriate model characteristics

Abstract

A processing circuit may comprise an adaptive filter having a response generating an anti-noise signal from a reference microphone signal, a secondary path estimate filter modeling an electro-acoustic path of a source audio signal, a biasing portion that generates a scaled anti-noise signal by applying a scaling factor and the response of the secondary path estimate filter to the anti-noise signal, and a coefficient control block that shapes the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and the scaled anti-noise signal.

Claims

1. A personal audio device comprising:

a personal audio device housing;

a transducer coupled to the housing for reproducing an audio signal including both a source audio signal 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;

a reference microphone coupled to the housing for providing a reference microphone signal indicative of the ambient audio sounds;

an error microphone coupled to the housing in proximity to the transducer for providing an error microphone signal indicative of the acoustic output of the transducer and the ambient audio sounds at the transducer; and

a processing circuit comprising;

an adaptive filter having a response that generates an anti-noise signal from the reference microphone signal;

a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and have a response that generates a secondary path estimate from the source audio signal;

a biasing portion that generates a scaled anti-noise signal by applying a scaling factor and the response of the secondary path estimate filter to the anti-noise signal; and

a coefficient control block that shapes the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and the scaled anti-noise signal.

2. The personal audio device of claim 1, wherein the scaling factor has a value between 0 and 1.

3. The personal audio device of claim 1, wherein the scaling factor defines a gain, wherein the gain is the ratio of the anti-noise signal that would be generated by filter without the biasing portion to the anti-noise generated by filter with the biasing portion.

4. The personal audio device of claim 1, wherein the value of the scaling factor is a function of a distance between the personal audio device and a portion of the listener.

5. The personal audio device of claim 4, wherein the distance is an estimated distance between the transducer and the listener'"'"'s eardrum.

6. The personal audio device of claim 4, wherein:

the secondary path estimate filter is an adaptive filter, and the processing circuit further implements a secondary coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

the distance is determined based on the response of the secondary path estimate filter.

7. The personal audio device of claim 1, wherein the value of the scaling factor is a function of a pressure applied to the personal audio device by the listener.

8. The personal audio device of claim 7, wherein the pressure is a pressure applied between the personal audio device and the listener'"'"'s ear.

9. The personal audio device of claim 7, wherein:

the secondary path estimate filter is adaptive, and the processing circuit further implements a secondary coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

the pressure is determined based on the response of the secondary path estimate filter.

10. A method for canceling ambient audio sounds in the proximity of a transducer of a personal audio device, the method comprising:

receiving a reference microphone signal indicative of the ambient audio sounds;

receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer; and

generating a source audio signal for playback to a listener;

adaptively generating an anti-noise signal, from a result of the measuring with the reference microphone, countering the effects of ambient audio sounds at an acoustic output of the transducer by adapting a response of an adaptive filter that filters the reference microphone signal in conformity with the reference microphone signal and a modified playback corrected error signal to minimize the ambient audio sounds in the error microphone;

generating a secondary path estimate from the source audio signal by filtering the source audio signal with a secondary path estimate filter modeling an electro-acoustic path of the source audio signal;

generating a scaled anti-noise signal by applying a scaling factor and a response of the secondary path estimate filter to the anti-noise signal; and

combining the anti-noise signal with a source audio signal to generate an audio signal provided to the transducer;

wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and the scaled anti-noise signal.

11. The method of claim 10, wherein the scaling factor has a value between 0 and 1.

12. The method of claim 10, wherein the scaling factor defines a gain, wherein the gain is the ratio of the anti-noise signal that would be generated by filter without the biasing portion to the anti-noise generated by filter with the biasing portion.

13. The method of claim 10, wherein the value of the scaling factor is a function of a distance between the personal audio device and a portion of the listener.

14. The method of claim 13, wherein the distance is an estimated distance between the transducer and the listener'"'"'s eardrum.

15. The method of claim 13, further comprising:

shaping the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

determining the distance based on the response of the secondary path estimate filter.

16. The method of claim 10, wherein the value of the scaling factor is a function of a pressure applied to the personal audio device by the listener.

17. The method of claim 16, wherein the pressure is a pressure applied between the personal audio device and the listener'"'"'s ear.

18. The method of claim 16, further comprising:

shaping the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

determining the pressure based on the response of the secondary path estimate filter.

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

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

a reference microphone input for receiving a reference microphone signal indicative of the ambient audio sounds;

an error microphone input for receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer; and

a processing circuit comprising;

an adaptive filter having a response that generates an anti-noise signal from the reference microphone signal;

a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and have a response that generates a secondary path estimate from the source audio signal;

a biasing portion that generates a scaled anti-noise signal by applying a scaling factor and the response of the secondary path estimate filter to the anti-noise signal; and

a coefficient control block that shapes the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and the scaled anti-noise signal.

20. The integrated circuit of claim 19, wherein the scaling factor has a value between 0 and 1.

21. The integrated circuit of claim 19, wherein the scaling factor defines a gain, wherein the gain is the ratio of the anti-noise signal that would be generated by filter without the biasing portion to the anti-noise generated by filter with the biasing portion.

22. The integrated circuit of claim 19, wherein the scaling factor is a function of a distance between the personal audio device and a portion of the listener.

23. The integrated circuit of claim 22, wherein the distance is an estimated distance between the transducer and the listener'"'"'s eardrum.

24. The integrated circuit of claim 22, wherein:

the secondary path estimate filter is an adaptive filter, and the processing circuit further implements a secondary coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

the distance is determined based on the response of the secondary path estimate filter.

25. The integrated circuit of claim 19, wherein the scaling factor is a function of a pressure applied to the personal audio device by the listener.

26. The integrated circuit of claim 25, wherein the pressure is a pressure applied between the personal audio device and the listener'"'"'s ear.

27. The integrated circuit of claim 25, wherein:

the secondary path estimate filter is adaptive, and the processing circuit further implements a secondary coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and

the pressure is determined based on the response of the secondary path estimate filter.