ACTIVE NOISE CONTROL WITH COMPENSATION FOR ERROR SENSING AT THE EARDRUM

• US 20140044275A1
• Filed: 08/13/2013
• Published: 02/13/2014
• Est. Priority Date: 08/13/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Azmi, Yacine, Goldstein, Andre L., Andersen, Esge B.
• Granted Patent: US 9,516,407 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• 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 2420/07 Applications of wireless loudspeakers or wireless microphones
• CPC Class Codes: H04R 3/002 Damping circuit arrangements for transducers, e.g. motional feedback circuits
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

A personal listening system has an active noise control (ANC) controller that produces an anti-noise signal. A head worn audio device for a user has a speaker to convert the anti-noise signal into anti-noise, an error microphone, and a reference microphone. The controller uses signals from the error and reference microphones to produce the anti-noise signal in accordance with an adaptive filter algorithm that has an adjustable parameter which changes so as to move the point at which acoustic cancellation occurs from the error microphone and closer to the user'"'"'s eardrum. Other embodiments are also described and claimed.

Claims

1. A personal listening system comprising:

an active noise control (ANC) controller to produce an anti-noise signal; and

a head worn audio device to be worn by a user, the device having a speaker to convert the anti-noise signal into anti-noise, an error microphone and a reference microphone,

the ANC controller to use signals from the error and reference microphones to produce the anti-noise signal in accordance with an adaptive filter algorithm that tries to cancel ambient noise, that can be heard by the user, using the anti-noise, wherein the ANC controller has an adjustable ANC parameter which changes so as to move the point at which cancellation occurs, between the anti-noise and the ambient noise, from the error microphone closer to the user'"'"'s ear drum.

2. The system of claim 1 wherein the adjustable ANC parameter is used by the ANC controller to determine a frequency response of a filter model Sv′

(z) which estimates a path from an input of the speaker to an output of a virtual error sensor that would be located at the user'"'"'s ear drum.

3. The system of claim 1 further comprising a subjective tuning module that captures the user'"'"'s listening experience and on that basis adjusts the ANC parameter.

4. The system of claim 3 wherein the subjective tuning module comprises a user interface program that when executed by a processor prompts the user, via text displayed on a display screen, to provide manual user input while listening to their desired audio content, in an attempt to find the most comfortable noise cancellation setting, and converts the manual user input into the adjustable ANC parameter.

5. The system of claim 4 further comprising a touch screen of which the display screen is a part, wherein the user interface program is to produce a virtual slider or virtual knob on the touch screen whose sweep has been mapped to that of the adjustable ANC parameter.

6. The system of claim 5 wherein the slider is one dimensional and the module is programmed to map the slider to a pair of adjustable ANC parameters that are used by the ANC controller to move the point at which cancellation occurs, between the anti-noise and the ambient noise, from the error microphone closer to the user'"'"'s ear drum.

7. The system of claim 6 wherein the pair of adjustable ANC parameters that are mapped to the one dimensional slider are ear canal length and diameter.

8. The system of claim 5 wherein the slider is two dimensional and the module is programmed to map a first dimension of the slider to ear canal length as a first adjustable ANC parameter, and a second dimension of the slider to ear canal diameter as a second adjustable ANC parameter.

9. The system of claim 3 wherein the ANC controller has a pair of adjustable ANC parameters that represent ear canal length and ear canal diameter and which change, in response to the captured user'"'"'s listening experience, so as to move the anti-noise cancellation point closer to the user'"'"'s eardrum.

10. The system of claim 1 further comprising an audio signal source to produce an audio user content signal, wherein the speaker is coupled to convert the audio user content signal into user content sound.

11. The system of claim 10 wherein the audio signal source is part of a desktop computer, a smart phone, a tablet computer, a notebook computer, a wearable computing device, and a home audio video entertainment system.

12. The system of claim 10 wherein the speaker is part of a loose fitting or sealing-type in-ear headphone.

13. An electronic device for active noise control (ANC) of a sound disturbance, with compensation for virtual error sensing, comprising:

a controller to produce an anti-noise signal in a virtual error sensing mode of operation, by performing an adaptive filter algorithm that is based on a plurality of transfer functions including Pe′

(z), Se′

(z) and Sv′

(z) wherein Pe′

(z) and Se′

(z) are estimates of primary and secondary path transfer functions to an actual error sensor, and Pv′

(z) and Sv′

(z) are estimates of primary and secondary path transfer functions to a virtual error sensor, and

wherein the controller stores a baseline version of a compensating virtual mode transfer function that contains one of Pv′

(z)/Pe′

(z) and Sv′

(z)/Se′

(z), the baseline version having been determined offline in a laboratory setting, and is to adjust the compensating virtual mode transfer function online in accordance with manual input from a user that represents the user'"'"'s listening experience of the anti-noise signal and the disturbance, while the controller is operating in the virtual error sensing mode.

14. The device of claim 13 wherein the controller is to compute Se′

(z) online during the user'"'"'s listening experience of the anti-noise signal.

15. The device of claim 13 wherein the controller comprises an adaptive filter controller that adapts a W filter which produces the anti-noise signal, based on 1) an Sv′

(z) filtered version of a reference signal from a reference microphone and

     2) a difference between a) an Sv′

(z) filtered version of the anti-noise signal and b) a prediction of how the disturbance would be picked up by the virtual error sensor.

16. The device of claim 13 wherein the compensating virtual mode transfer function contains Pv′

(z)/Pe′

(z) and the controller treats Sv′

(z)/Se′

(z) and Pv′

(z)/Pe′

(z) as equals, the controller to compute Sv′

(z) by combining Se′

(z) with Cvm(z).

17. A personal listening system comprising:

an active noise control (ANC) controller to produce an anti-noise signal that is to be converted into anti-noise by a speaker in a head worn audio device to be worn by a user,

the ANC controller to use signals from error and reference microphones in the head worn audio device and a plurality of transfer functions to produce the anti-noise signal, in accordance with an adaptive filter algorithm that tries to cancel ambient noise that can be heard by the user using the anti-noise, wherein the plurality of transfer functions include Pe′

(z), Se′

(z), Pv′

(z), and Sv′

(z), wherein a ratio of Pe′

(z) and Pv′

(z) has a baseline which was determined offline in a laboratory setting and then stored in the system and wherein the ratio is adjusted online, while the device is being worn by the user and user content and the anti-noise are being produced by the speaker.

18. The system of claim 17 wherein in the ANC controller the ratio of Pe′

(z) and Pv′

(z) is treated as being essentially equal to a ratio of Se′

(z) to Sv′

(z).

19. The system of claim 18 wherein the ANC controller computes Se′

(z) online while one of test sounds and user content is being produced by the speaker.

20. The system of claim 17 wherein the adaptive filter algorithm is a filtered-x LMS feed forward algorithm.

21. A method for active noise control (ANC) in a personal listening device, comprising:

initializing an ANC process for operation in virtual error sensing mode, by loading a pre-determined generic for one of the following transfer functions, Pv′

(z), Sv′

(z), Pv′

(z)/Pe′

(z) and Sv′

(z)/Se′

(z);

performing the ANC process using the loaded generic transfer function;

obtaining manual input selected by a user of the personal listening device;

converting the obtained manual input to one or more ANC parameters;

determining a new version of said one of the transfer functions based on the ANC parameters selected by the user; and

applying the new version of said transfer function to the ANC process being performed.

22. The method of claim 21 wherein performing the ANC process comprises:

producing an anti-noise signal, that is to be converted into anti-noise by a speaker in a head worn audio device that is worn by the user, using an adaptive filter;

filtering a reference signal in accordance with the secondary path transfer function Sv′

(z);

filtering a residual noise signal, obtained from an error mic in the head worn audio device, in accordance with a ratio of Pv′

(z) and Pe′

(z); and

adjusting the adaptive filter in accordance with an adaptive filter algorithm that uses a difference between the filtered residual noise signal and a Sv′

(z) filtered version of the anti-noise signal.

23. The method of claim 21 wherein determining a new version of the transfer function comprises one of performing a table lookup and computing directly a plurality of digital filter coefficients of a digital filter that represents the new version of the transfer function.

24. A method for active noise control (ANC) in a personal listening device, comprising:

executing an acoustic impedance measurement program in the personal listening device that measures the acoustic input impedance of the user'"'"'s ear canal, while the user is wearing a head worn device of the personal listening system;

determining a compensating virtual sensing mode transfer function that contains one of Pv′

(z), Sv′

(z), Pv′

(z)/Pe′

(z) and Sv′

(z)/Se′

(z), based on the measured input impedance; and

applying the transfer function to an ANC process in the personal listening system, while the user is wearing the head worn device.

25. The method of claim 24 further comprising:

obtaining manual input selected by the user while the ANC process configured with the transfer function is running;

converting the manual input selected by the user to a plurality of ANC parameters representing ear canal length and ear canal diameter;

determining a new version of said transfer function based on the ANC parameters as selected by the user; and

applying the new version of the transfer function to the running ANC process.