ACTIVE NOISE CANCELLATION DECISIONS IN A PORTABLE AUDIO DEVICE

• US 20110299695A1
• Filed: 06/04/2010
• Published: 12/08/2011
• Est. Priority Date: 06/04/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Nicholson, Guy C.
• Granted Patent: US 8,515,089 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• CPC Class Codes: G10K 11/175 using interference effects; Masking sound
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• 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 11/17835 using detection of abnormal input signals
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• 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 2210/3026 Feedback

Abstract

Active noise cancellation (ANC) circuitry is coupled to the input of an earpiece speaker in a portable audio device, to control the ambient acoustic noise outside of the device and that may be heard by a user of the device. A microphone is to pickup sound emitted from the earpiece speaker, as well as the ambient acoustic noise. Control circuitry deactivates the ANC in response to determining that an estimate of how much sound emitted from the earpiece speaker has been corrupted by noise indicates insufficient corruption by noise. In another embodiment, the ANC decision is in response to determining that an estimate of the ambient noise level is greater than a threshold level of an audio artifact that could be induced by the ANC. Other embodiments are also described and claimed.

Claims

1. A portable audio device comprising:

an earpiece speaker having an input to receive an audio signal;

active noise cancellation (ANC) circuitry to provide an anti-noise signal at the input of the earpiece speaker to control ambient acoustic noise outside of the device that is heard by a user of the device; and

noise measurement circuitry having a first input coupled to an output of a first microphone and a second input coupled to receive the audio signal and the anti-noise signal, the first microphone to pick up (a) sound emitted from the earpiece speaker and (b) the ambient acoustic noise; and

control circuitry coupled to receive an estimate of the ambient acoustic noise from the noise measurement circuitry and to deactivate the ANC circuitry in response to determining that an estimate of how much sound emitted from the earpiece speaker has been corrupted by said ambient acoustic noise, indicates insufficient corruption by noise.

2. The portable audio device of claim 1 wherein the ANC circuitry comprises an anti-noise filter that inverts a signal at its input, the input being coupled to receive the estimate of the ambient acoustic noise.

3. The portable audio device of claim 1 wherein the ANC circuitry comprises a second microphone to pick up the ambient acoustic noise, wherein the first microphone is positioned closer to the earpiece speaker than the second microphone, and an adaptive filter that generates the anti-noise signal using a representation of the ambient acoustic noise as picked up by the second microphone

4. The portable audio device of claim 1 wherein the control circuitry is to calculate signal to noise ratio (SNR) as referring to the audio signal and said ambient acoustic noise, and wherein the control circuitry is to deactivate the ANC circuitry when the calculated SNR is above a predetermined threshold.

5. The portable audio device of claim 3 wherein the noise measurement circuitry comprises:

a first filter that models the earpiece speaker and the first microphone, wherein the audio signal and the anti-noise signal are to pass through the first filter;

a differencing unit having a first input coupled to the output of the first microphone and a second input coupled to an output of the first filter; and

a second filter that models the earpiece speaker and the first microphone, wherein the audio signal is to pass through the second filter.

6. The portable audio device of claim 5 wherein the control circuitry comprises:

a smoothing conditioner to smooth the signals from outputs of the second filter and the differencing unit; and

a decision circuit having first and second inputs coupled to receive the smoothed signals, respectively, and an output that indicates whether or not the ANC circuitry is to be deactivated.

7. The portable audio device of claim 6 wherein the control circuitry is to calculate signal to noise ratio (SNR) using the smoothed signals, and wherein the control circuitry is to deactivate the ANC circuitry when the calculated SNR is above a predetermined threshold.

8. The portable audio device of claim 1 wherein the ANC circuitry when activated can enhance intelligibility of a far-end user'"'"'s speech contained in the audio signal and as heard by a near-end user of the device through the earpiece speaker, during a call between the far-end user and the near-end user.

9. A portable audio device comprising:

an earpiece speaker having an input to receive an audio signal;

active noise cancellation (ANC) circuitry coupled to the input of the earpiece speaker to control ambient acoustic noise outside of the device that is heard by a user of the device; and

control circuitry to compute strength of an audio artifact present in sound emitted from the earpiece speaker,

wherein the control circuitry is to deactivate the ANC circuitry in response to determining that the audio artifact strength is greater than an estimated level of said ambient acoustic noise.

10. The portable audio device of claim 9 further comprising:

noise measurement circuitry to determine an estimate of the ambient acoustic noise, the noise measurement circuitry having

a first microphone to pickup (a) sound emitted from the earpiece speaker and (b) said ambient acoustic noise,

a first filter that models acoustic response at the output of the speaker and pick up by the first microphone, the first filter having an input coupled to receive the audio signal and an anti-noise signal produced by the ANC circuitry,

a second filter having a similar frequency response as the first filter, wherein the audio signal is to pass through the second filter, and

a differencing unit having a first input coupled to the output of the first microphone and a second input coupled to an output of the first filter, the differencing unit having an output representing the estimate of the ambient acoustic noise,

and wherein the control circuitry has an input coupled to an output of the differencing unit from which to compute the audio artifact strength.

11. The portable audio device of claim 9 wherein the control circuitry is to determine the audio artifact strength above an effective frequency range of the ANC circuitry.

12. A method for performing a call using a portable audio communications device comprising:

activating active noise cancellation (ANC) circuitry to control ambient acoustic noise during the call;

determining that an estimate of how much sound emitted from an earpiece speaker of the device has been corrupted by said ambient acoustic noise indicates insufficient corruption by noise; and

deactivating the ANC circuitry in response to the determination.

13. The method of claim 12 and wherein the determining comprises comparing signal to noise ratio (SNR), referring to downlink speech signal and the ambient acoustic noise, to a predetermined threshold to find that the SNR is greater than the predetermined threshold.

14. The method of claim 12 wherein the deactivating the ANC circuitry comprises:

setting a plurality of tap coefficients of a digital anti-noise filter whose output feeds the earpiece speaker, to zero.

15. The method of claim 14 wherein the deactivating the ANC circuitry further comprises:

disabling an adaptive filter controller that updates the tap coefficients, so that the tap coefficients are no longer being updated.

16. The method of claim 12 wherein the deactivating the ANC circuitry comprises:

disabling an adaptive filter controller that updates a plurality of tap coefficients of a digital anti-noise filter, so that the tap coefficients are no longer being updated.

17. A method for performing a call using a portable audio communications device, comprising:

a) determining that an estimate of how much sound emitted from an earpiece speaker of the device during the call has been corrupted by ambient acoustic noise, indicates sufficient corruption by noise;

b) in response to the determination in a), activating active noise cancellation (ANC) circuitry to control the ambient acoustic noise during the call; and

then

c) determining that an estimate of how much sound emitted from the earpiece speaker during the call has been corrupted by ambient acoustic noise indicates insufficient corruption by noise; and

d) deactivating the ANC circuitry in response to the determination in c).

18. A method for performing a call using a portable audio communications device, comprising:

estimating ambient acoustic noise heard by a user of the portable communications device during the call;

determining an audio artifact threshold which indicates strength of an audio artifact that could be induced by the ANC circuitry and heard by a user of the device after being emitted from an earpiece speaker of the device; and

deactivating ANC circuitry during the call in response to the estimated noise level being less than the audio artifact threshold.

19. The method of claim 18 wherein the determining an audio artifact threshold comprises loading a predetermined hiss threshold.

20. The method of claim 18 further comprising:

activating the ANC circuitry during the call in response to the estimated noise level being greater than the audio artifact threshold.

21. A portable audio device comprising:

a mobile phone handset having integrated therein an earpiece speaker, the earpiece speaker having an input coupled to receive a downlink speech signal, and a detector that can indicate when the handset is being held against a user'"'"'s ear and when it is not;

active noise cancellation (ANC) circuitry coupled to the input of the earpiece speaker to control ambient acoustic noise outside of the device that is heard by a user of the device; and

ANC decision control circuitry coupled to the detector and the ANC circuitry, to deactivate the ANC circuitry when the detector indicates the handset is not being held against the user'"'"'s ear.