ADAPTIVE AUDIO EQUALIZATION FOR PERSONAL LISTENING DEVICES

• US 20140341388A1
• Filed: 05/16/2013
• Published: 11/20/2014
• Est. Priority Date: 05/16/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Goldstein, Andre L., Bajic, Vladan
• Granted Patent: US 9,515,629 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• 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 11/1785 Methods, e.g. algorithms; Devices G10K11/1781, G10K11/1783 take precedence
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• 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 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3055 Transfer function of the acoustic system
• CPC Class Codes: G10K 2210/51 Improving tonal quality, e.g. mimicking sports cars
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 2410/05 Noise reduction with a separate noise microphone
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

An audio processor has an active noise cancellation (ANC) processor to compute an S-filter, which estimates a transfer function from an earpiece speaker, that is to be worn by a user, to an error microphone. The ANC processor adaptively produces an anti noise signal for reducing ambient noise that can be heard by the user. An adaptive equalization (EQ) processor has an EQ filter controller that adjusts an EQ filter, while audio user content is being filtered in accordance with the EQ filter before being fed to the speaker and then heard by the user. Other embodiments are also described and claimed.

Claims

1. An audio processor comprising:

an adaptive S-filter which estimates a transfer function from an earpiece speaker, that is to be worn by a user, to an error microphone;

an S-filter controller to compute the adaptive S-filter;

an adaptive EQ filter; and

an EQ filter controller that is to adaptively adjust the EQ filter, while audio user content is being filtered in accordance with the EQ filter before being fed to the speaker and then heard by the user.

2. The audio processor of claim 1 further comprising a signal generator to produce a dummy signal that is to pass through the EQ filter and a copy of the S-filter and then be provided to the EQ filter controller, based on which the EQ filter controller adaptively adjusts the EQ filter.

3. The audio processor of claim 2 wherein the dummy signal is one of a white noise signal and a pink noise signal.

4. The audio processor of claim 1 further comprising a copy of the adaptive EQ filter through which the audio user content is to pass before being fed to an input of the S-filter.

5. The audio processor of claim 1 further comprising a copy of the S-filter that is used for input to the EQ filter controller.

6. The audio processor of claim 2 wherein the EQ filter controller is to compute signal power in a frequency band of the EQ- and S-filtered dummy signal that is below 2 kHz, and based on a comparison of the computed signal power adjust gain of a shelf filter being a constituent filter block of the EQ filter.

7. The audio processor of claim 6 wherein the EQ filter controller is to smooth the computed signal power over time before comparing to a target, based on which the gain of the shelf filter is adjusted.

8. The audio processor of claim 6 wherein the shelf filter is a low frequency shelf filter that has variable gain in a low frequency band and essentially zero gain in a high frequency band.

9. The audio processor of claim 1 further comprising an adaptive W-filter to produce an anti-noise signal for reducing ambient noise that can be heard by the user, a W-filter controller coupled to adjust the W-filter, and a copy of the S-filter through which a signal from a reference microphone is to pass before being fed to an input of the W-filter controller.

10. The audio processor of claim 9 wherein the anti-noise signal is combined with the audio user content coming from a copy of the EQ filter, before being fed to the speaker.

11. The audio processor of claim 10 wherein the EQ filter controller computes signal power in a low frequency band and signal power in a high frequency band of the EQ and S-filtered dummy signal, and based on a comparison of the computed signal powers adjusts gain of a shelf filter being a constituent filter block of the EQ filter.

12. A method for audio processing, comprising:

initializing an adaptive S-filter which is to be used to estimate a transfer function from an earpiece speaker, that is being used by a user, to an error microphone;

initializing an adaptive EQ-filter which is to be used to correct user audio content being fed to the speaker and then heard by the user so as to compensate for variable acoustic sealing around the earpiece speaker against the user'"'"'s ear;

filtering the user audio content in accordance with the EQ filter and the S-filter, and then using the EQ and S filtered user audio content to produce an error signal from a signal from the error microphone;

adjusting the EQ filter, while the user audio content being fed to the speaker is corrected in accordance with the EQ filter; and

adjusting the S-filter based on the user audio content and based on the error signal.

13. The method of claim 12 wherein filtering the user audio content in accordance with the EQ filter and the S-filter comprises passing audio user content through a copy of the EQ filter.

14. The method of claim 12 wherein adjusting the EQ filter comprises

producing a dummy signal and filtering the dummy signal in accordance with the EQ filter and the S-filter;

and

adjusting the EQ filter based on the EQ- and S-filtered dummy signal.

15. The method of claim 14 wherein adjusting the EQ filter based on the EQ- and S-filtered dummy signal comprises:

computing signal power in a low frequency band and signal power in a high frequency band of the EQ- and S-filtered dummy signal;

comparing the computed signal powers; and

adjusting a digital filter coefficient of the EQ filter based on the comparison.

16. The method of claim 14 wherein adjusting the EQ filter based on the EQ- and S-filtered dummy signal comprises:

computing signal power in a frequency band of the EQ- and S-filtered dummy signal;

comparing the computed signal power with a target; and

adjusting a digital filter coefficient of the EQ filter based on the comparison.

17. The method of claim 12 further comprising:

producing an anti noise signal for reducing ambient noise that can be heard by the user; and

filtering a signal from a reference microphone in accordance with the S-filter; and

adjusting the anti-noise signal based on the error signal.

18. The method of claim 17 further comprising:

combining the anti-noise signal with the user audio content that has been corrected in accordance with the EQ filter, before feeding the speaker.

19. An audio device that can perform online adaptive equalization (EQ) of user audio content, comprising:

an audio signal interface circuit that is to receive an audio signal from an error microphone, and that is to send an audio signal to an earpiece speaker;

an S-filter controller to compute an adaptive S-filter which estimates a transfer function from the earpiece speaker to the error microphone;

an EQ filter controller that is to adjust an adaptive EQ filter, while user audio content is being passed through a copy of the EQ filter before being sent to the speaker,

wherein the S-filter controller is to adjust the adaptive S-filter based on the user audio content and based on a signal from the error microphone, while the audio user content is being passed through a copy of the adaptive EQ filter and through the adaptive S-filter.

20. The audio device of claim 19 further comprising an accessory connector into which a wired headset can be plugged,

wherein the audio signal interface circuit comprises circuitry that is coupled to the accessory connector to receive the audio signal from the error microphone when the headset has been plugged in, and circuitry that is coupled to the accessory connector to send the audio signal to the speaker when the headset has been plugged in.

21. The audio device of claim 20 in combination with the wired headset.

22. The audio device of claim 19 wherein the EQ filter controller is to perform per frequency bin digital signal processing of a) the audio user content before the audio user content is corrected by the adaptive EQ filter, and b) the signal from the error microphone, to compute powers of the audio user content and of error microphone signal in a frequency bin and compare the computed powers on then on that basis adjust gain of the EQ filter in said frequency bin.