ACTIVE NOISE CANCELLATION USING MULTIPLE REFERENCE MICROPHONE SIGNALS

• US 20140086425A1
• Filed: 09/24/2013
• Published: 03/27/2014
• Est. Priority Date: 09/24/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Jensen, Thomas M., Bajic, Vladan, Bright, Andrew P.
• Granted Patent: US 9,330,652 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• 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 11/17821 characterised by the analysis of the input signals only
• CPC Class Codes: G10K 11/17825 Error signals
• 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 11/17854 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 2210/3018 Correlators, e.g. convolvers or coherence calculators
• CPC Class Codes: G10K 2210/3056 Variable gain

Abstract

In one aspect, multiple adaptive W filters and associated adaptive filter controllers are provided that use multiple reference microphone signals to produce multiple, “component” anti-noise signals. These are gain weighted and summed to produce a single anti-noise signal, which drives an earpiece speaker. The weighting changes based on computed measures of the coherence between content in each reference signal and content in an error signal. Other embodiments are also described and claimed.

Claims

1. A portable personal listening audio device, comprising:

active noise cancellation (ANC) circuitry having

a plurality of adaptive filters each to produce a respective anti-noise signal using a respective one of a plurality of reference signals,

a plurality of adaptive filter controllers, wherein each controller is to adjust a respective one of the adaptive filters based on input from the respective reference signal and an error signal,

a combiner to produce a weighted sum of the anti-noise signals that is to then be converted to anti-noise sound, so as to control a disturbance being background acoustic noise that is heard by a user, and

an adaptive gain control block coupled to the combiner to adjust the weighting of each of the anti-noise signals based on coherence between content in a respective one of the reference signals and in the error signal.

2. The device of claim 1 further comprising:

a plurality of reference microphones to pick up ambient sound outside of the device, which is represented in the plurality of reference signals, respectively;

an error microphone to pick up residual acoustic noise, which is represented in the error signal; and

an earpiece speaker having an input to receive the weighted sum anti-noise signal.

3. The device of claim 1 wherein the adaptive gain control block is to compute a respective measure of coherence between content in a respective one of the reference signals and in an estimate of the disturbance derived from the error signal, and on that basis adjust the weighting of the respective anti-noise signal.

4. The device of claim 3 wherein the combiner is to produce the weighted sum of the anti-noise signals by applying a respective, full frequency band gain or scaling factor to the respective anti-noise signal, and wherein the adaptive gain control block comprises a coherence-based gain controller that computes the respective scaling factor.

5. The device of claim 1 further comprising an error signal correction block to adjust the error signal, before input to the adaptive filter controllers, so as to counteract the combiner'"'"'s weighting of the anti-noise signals.

6. The device of claim 5 wherein the error signal block comprises a plurality of variable gain blocks each to apply a gain, to a respective one of the anti-noise signals, that is complementary to the weighting applied by the combiner to said one of the anti-noise signals.

7. The device of claim 2 further comprising a mobile phone handset housing in which the earpiece speaker is installed as a receiver, together with one of the plurality of reference microphones and the error microphone.

8. The device of claim 2 further comprising an earphone housing in which the earpiece speaker is integrated together with the error microphone and one of the plurality of reference microphones.

9. A portable personal listening audio device, comprising:

active noise cancellation (ANC) circuitry having

a combiner to produce a weighted sum of a plurality of reference signals,

an adaptive filter to produce an anti-noise signal using the weighted sum reference signal to control a disturbance being ambient sound that is heard by a user,

an adaptive filter controller to adjust the adaptive filter based on input from the weighted sum reference signal and an error signal, and

an adaptive gain control block coupled to the combiner to compute a measure of coherence between content in a respective one of the reference signals and in the error signal and on that basis adjust a weighting of the respective reference signal.

10. The device of claim 9 wherein the adaptive gain control block comprises a coherence-based gain controller that receives the reference signals, and a difference block that estimates the disturbance by subtracting an estimate of the anti-noise sound from the error signal.

11. A portable personal listening audio device comprising:

an active noise cancellation (ANC) processor having;

a plurality of adaptive filters, each to produce to a respective anti-noise signal using a respective one of a plurality of reference signals,

a plurality of adaptive filter controllers, each to adjust a respective one of the adaptive filters, based on input from the respective reference signal and from an error signal,

a combiner to produce a sum of the anti-noise signals that is to be converted to anti-noise sound so as to control a disturbance being ambient sound that is heard by a user, and

a coherence-based leakage control block that is coupled to each of the adaptive filter controllers to adjust a weighting factor used by the adaptive filter controller when computing an update to filter coefficients of the respective adaptive filter, responsive to computing a measure of coherence between content in the respective reference signal and content in the error signal.

12. The device of claim 11 wherein the coherence-based leakage control block is to compute said measure of coherence between the respective reference signal and the error signal by computing an estimate of the disturbance, using the error signal, and computing a measure of coherence between the respective reference signal and the estimated disturbance.

13. The device of claim 12 wherein the coherence-based leakage control block comprises a leakage calculator that determines a respective leakage parameter to be used by the adaptive filter controllers when updating the filter coefficients of the respective adaptive filter, and a difference block having an input to receive the error signal and another input to receive a filtered version of the sum anti-noise signal that has been filtered in accordance with an estimate of a secondary path transfer function.

14. The device of claim 13 wherein the coherence-based leakage calculator comprises one of a lookup table and a mathematical formula that relates a coherence parameter, representing coherence between the respective reference signal and the estimated disturbance, to the leakage parameter in such a way that the leakage parameter is determined to be small when the coherence parameter is large and the leakage parameter is determined to be large when the coherence parameter is small.

15. A method for active noise cancellation in a portable personal listening audio device, comprising:

producing a plurality of component anti-noise signals using a plurality of adaptive filters and a plurality of reference signals, respectively, wherein the reference signals reflect pickup of background sound by a plurality of microphones, respectively, of the personal listening audio device;

adjusting coefficients of the adaptive filters based on input from the reference signals and based on input from a signal from an error microphone;

computing a respective measure of coherence between content in each of the reference signals and content in the signal from the error microphone; and

producing a weighted sum of the component anti-noise signals wherein weighting of the component anti-noise signals changes as a function of the computed respective measure of coherence.

16. The method of claim 15 further comprising computing an estimate of a disturbance, being the background sound as would be heard by a user of the portable personal listening audio device while excluding effects of anti-noise, using the signal from the error microphone, wherein computing the respective measure of coherence comprises computing a measure of coherence between the respective reference signal and the estimated disturbance.

17. The method of claim 15 further comprising producing an error signal from the signal from the error microphone, and adjusting the error signal to counteract the weighting of the component anti-noise signals, wherein adjusting the coefficients of the adaptive filters is based on the adjusted error signal.

18. The method of claim 15 further comprising:

receiving manual user input regarding active noise cancellation (ANC) strength that can be in a range of no ANC to full strength ANC;

mapping the received user input to a scaling factor; and

applying the scaling factor to the weighted sum anti-noise signal.

19. A method for active noise cancellation in a portable personal listening audio device, comprising:

producing a plurality of component anti-noise signals using a plurality of adaptive filters and a plurality of the reference signals, respectively;

updating coefficients of the adaptive filters based on input from the reference signals and based on a signal from an error microphone;

computing a respective measure of coherence between content in each of the reference signals and content in the signal from the error microphone, and in response adjusting a weighting factor used when updating the coefficients of the adaptive filters; and

combining the component anti-noise signals.

20. The method of claim 19 further comprising computing an estimate of a disturbance, being background sound as would be heard by a user of the portable listening audio device, using the signal from the error microphone, wherein computing the respective measure of coherence comprises computing a measure of coherence between the respective reference signal and the estimated disturbance.

21. The method of claim 19 further comprising:

receiving manual user input regarding active noise cancellation (ANC) strength that can be in a range between no ANC and full strength ANC;

mapping the received user input to a scaling factor; and

applying the scaling factor to the combined anti-noise signals.