Active noise cancellation decisions in a portable audio device

• US 9,330,654 B2
• Filed: 05/16/2013
• Issued: 05/03/2016
• Est. Priority Date: 06/04/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Nicholson, Guy C.
• Primary Examiner(s): Lee, Ping
• Application Number:
  US13/895,659
• Publication Number:
  US 20130252675A1
• Time in Patent Office: 1,083 Days
• Field of Search: 381/71.6, 381/71.8, 381/71.11, 381/71.12, 381/74
• US Class Current: 1/1
• 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 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, the audio artifact induced by operation of the ANC circuitry above an effective frequency range of the ANC circuitry,

wherein the control circuitry is to deactivate the ANC circuitry in response to determining that the audio artifact strength is greater than a level of said ambient acoustic noise estimated from a measurement of a combination of sound emitted from the earpiece speaker and said ambient acoustic noise.

2. The portable audio device of claim 1 further comprising:

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

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

a first filter that models acoustic response at an output of the earpiece 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, and

a differencing unit having a first input coupled to an 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 the output of the differencing unit from which to compute the estimated level of said ambient acoustic noise.

3. The portable audio device of claim 2 wherein the noise measurement circuitry further having a second filter having a similar frequency response as the first filter, wherein the audio signal is to pass through the second filter.

4. The portable audio device of claim 1, wherein the audio artifact is a hiss created by the ANC circuitry.

5. The portable audio device of claim 1, wherein the audio artifact strength comprises a predetermined hiss threshold.

6. The portable audio device of claim 1, wherein the control circuitry determines the audio artifact strength above 2 kHz.

7. The portable audio device of claim 1, wherein the control circuitry determines the estimated level of the ambient acoustic noise for noise in a frequency range having a low end between 300 Hz-500 Hz and a high end between 1.5 Hz-2 kHz.

8. The portable audio device of claim 1, wherein the ANC circuitry is to provide an anti-noise signal at the input of the earpiece speaker to control the ambient acoustic noise outside of the device that is heard by the user of the portable audio device, the portable audio device further comprising:

a first microphone to pick up the ambient acoustic noise;

a second microphone, wherein the second microphone is positioned closer to the earpiece speaker than the first microphone and is to pick up (a) sound emitted from the earpiece speaker and (b) the ambient acoustic noise; and

wherein the ANC circuitry includes

an adaptive filter that generates the anti-noise signal using a representation of the ambient acoustic noise as picked up by the first microphone, noise measurement circuitry having

an input coupled to an output of the second microphone,

a first filter that models a path from the earpiece speaker to the second microphone,

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

a second filter that models the path from the earpiece speaker to the second microphone,

wherein the noise measurement circuitry receives the audio signal and the anti-noise signal, the audio signal is to pass through the first and second filters, the anti-noise signal is to pass through the first filter; and

the control circuitry is 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.

9. The portable audio device of claim 1, further comprising noise measurement circuitry to determine an estimated level of the ambient acoustic noise by finding a difference between a measurement of sound emitted from the earpiece speaker and the ambient acoustic noise, and an estimate of sound emitted from the earpiece speaker based on the audio signal and an anti-noise signal produced by the ANC circuitry.

10. A method for performing a call using a portable audio communications device having active noise cancellation (ANC) circuitry, comprising:

estimating a noise level for ambient acoustic noise heard by a user of the portable audio communications device during the call from a measurement of a combination of sound emitted from an earpiece speaker of the device and said ambient acoustic noise;

determining an audio artifact threshold which indicates strength of an audio artifact that is induced by the ANC circuitry above an effective frequency range of the ANC circuitry and heard by the user of the device after being emitted from the earpiece speaker of the device; and

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

11. The method of claim 10 wherein the determining an audio artifact threshold comprises loading a predetermined hiss threshold.

12. The method of claim 10 further comprising:

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

13. The method of claim 10, wherein the audio artifact is a hiss created by the ANC circuitry.

14. The method of claim 10, further comprising:

activating the ANC circuitry so that an anti-noise signal is output to control the ambient acoustic noise during the call at the earpiece speaker of the portable audio communications device;

passing a downlink speech signal of the call through a filter that models a path from the earpiece speaker to an error microphone;

passing the anti-noise signal through the filter that models the path from the earpiece speaker to the error microphone

computing an estimate of the ambient acoustic noise using the filtered downlink speech signal and the filtered anti-noise signal;

determining, using the computed estimate of the ambient acoustic noise and the filtered downlink speech signal, that sound emitted from the earpiece speaker of the device is not being sufficiently corrupted by said ambient acoustic noise; and

deactivating the ANC circuitry in response to the determination.

15. The method of claim 10 wherein the determining the audio artifact threshold comprises computing the strength of the audio artifact by finding a difference between a measurement of sound emitted from the earpiece speaker and the ambient acoustic noise, and an estimate of sound emitted from the earpiece speaker based on an audio signal coupled to the earpiece speaker and an anti-noise signal produced by the ANC circuitry.