ANC SYSTEM WITH SPL-CONTROLLED OUTPUT

• US 20150071453A1
• Filed: 06/13/2014
• Published: 03/12/2015
• Est. Priority Date: 09/06/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Po, Bruce C., Bajic, Vladan
• Granted Patent: US 9,607,602 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/175 using interference effects; Masking sound
• CPC Class Codes: G10K 11/17815 between the reference signals and the error signals, i.e. primary path
• 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 11/1783 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 2210/3056 Variable gain

Abstract

An anti-noise signal is produced in accordance with an active noise cancellation process (ANC), at an input of a speaker so as to control how much background noise a user can hear. Strength of the anti-noise signal is adjusted gradually, rather than abruptly, in proportion to decreasing or increasing sound pressure level (SPL) of the background noise, during inactivation or activation of the ANC process. Other embodiments are also described and claimed.

Claims

1. A method for active noise cancellation (ANC), comprising:

estimating sound pressure level (SPL) of ambient noise; and

one of a) activating an ANC process and b) inactivating the ANC process, gradually, rather than abruptly, based on the estimated ambient noise SPL.

2. The method of claim 1 wherein gradually activating the ANC process comprises varying a strength of the ANC process as a function of the estimated ambient noise SPL, so that when the estimated ambient noise SPL is low the ANC process produces essentially no anti-noise and then produces anti-noise with gradually increasing strength when the estimated ambient noise SPL is medium and then produces anti-noise having greatest strength when the estimated ambient noise SPL is high.

3. The method of claim 1 wherein gradually activating or inactivating the ANC process comprises varying a strength of the ANC process by varying how filter coefficients of an adaptive digital filter W of the ANC process are updated by an adaptive algorithm.

4. The method of claim 3 further comprising updating the filter coefficients of the adaptive digital filter W in accordance with a leaky adaptive algorithm in which a current coefficient is computed based on weighting a prior coefficient, wherein the weighting is varied as a function of the estimated ambient noise SPL.

5. The method of claim 4 wherein the weighting contains a leakage parameter, and updating the filter coefficients comprises varying the leakage parameter as a function of the estimated ambient noise SPL.

6. The method of claim 4 wherein gradually activating the ANC process comprises starting with a small weighting when the estimated ambient noise SPL is low, and then gradually increasing the weighting as the estimated ambient noise SPL increases.

7. The method of claim 6 wherein gradually activating the ANC process comprises starting with a smallest, fixed weighting when the estimated background noise SPL is low, and then gradually increasing the weighting as the estimated ambient noise SPL is medium, and then maintaining a largest, fixed weighting when the estimated ambient noise SPL is high.

8. A portable electronic device comprising:

a speaker; and

an active noise cancellation (ANC) controller having an output coupled to the speaker, the ANC controller having an adaptive filter that is to produce an anti-noise signal to be converted by the speaker for controlling how much background noise can be heard by a user, wherein the ANC controller raises strength of the anti-noise signal gradually, rather than abruptly, in proportion to increasing sound pressure level of the background noise between ANC being activated until ANC is at full strength.

9. The device of claim 8 wherein the ANC controller lowers strength of the anti-noise signal gradually, rather than abruptly, in proportion to decreasing sound pressure level of the background noise between when ANC is at full strength until ANC is inactivated.

10. The device of claim 8 wherein the ANC controller is to gradually raise strength of the anti-noise signal by varying how filter coefficients of an adaptive digital filter that produces the anti-noise signal are updated by an adaptive algorithm.

11. The device of claim 10 wherein the ANC controller is to update the filter coefficients of the adaptive digital filter in accordance with a leaky adaptive algorithm in which a current coefficient is computed based on weighting a prior coefficient, wherein the weighting is a function of the estimated background noise SPL.

12. The device of claim 11 wherein the weighting contains a leakage parameter, and updating the filter coefficients comprises varying the leakage parameter as a function of the estimated background noise SPL.

13. The device of claim 8 further comprising an earphone housing or a smartphone handset housing in which the speaker is integrated.

14. A portable electronic device comprising:

a speaker; and

an active noise cancellation (ANC) controller having an output coupled to the speaker, the ANC processor having an adaptive filter that is to produce an anti-noise signal to be converted by the speaker for controlling how much background noise can be heard by a user, wherein the ANC processor lowers strength of the anti-noise signal gradually, rather than abruptly, in proportion to decreasing sound pressure level of the background noise between when ANC is at full strength until ANC is inactivated.

15. The portable electronic device of claim 14 wherein the ANC controller is to gradually raise strength of the anti-noise signal by varying how filter coefficients of an adaptive digital filter that produces the anti-noise signal are updated by an adaptive algorithm.

16. The device of claim 15 wherein the ANC controller is to update the filter coefficients of the adaptive digital filter in accordance with a leaky adaptive algorithm in which a current coefficient is computed based on weighting a prior coefficient, wherein the weighting is a function of the estimated background noise SPL.

17. The device of claim 16 wherein the weighting contains a leakage parameter, and updating the filter coefficients comprises varying the leakage parameter as a function of the estimated background noise SPL.

18. A portable electronic device comprising:

means for converting an audio signal into sound;

means for producing an anti-noise signal at an input of the conversion means to control how much background noise can be heard by a user;

means for adaptively controlling the anti-noise signal production means; and

one of

a) means for raising strength of the anti-noise signal gradually, rather than abruptly, in proportion to increasing sound pressure level of the background noise between the adaptive control means being activated until the adaptive control means is at full strength, and

b) means for lowering strength of the anti-noise signal gradually, rather than abruptly, in proportion to decreasing sound pressure level of the background noise between when the adaptive control means is at full strength until the adaptive control means is inactivated.

19. The device of claim 18 wherein said anti-noise signal strength varying means causes the anti-noise signal to have a) greatest strength when the background noise SPL is high, b) gradually decreasing strength when the background noise SPL is medium, c) essentially no strength when the background noise SPL is low.

20. The device of claim 18 further comprising means for estimating SPL of the background noise, wherein the anti-noise signal strength varying means causes the adaptive control means to change how it computes updates to digital filter coefficients of the anti-noise signal production means, as a function of the estimated background noise SPL.