received by the International Bureau on 09 September 2015 (09.05.2015)

WHAT IS CLAIMED IS:

1. An integrated circuit for implementing at least a portion of a personal audio device, comprising:

a first output configured to provide a first output signal to a first transducer;

a second output configured to provide a second output signal to a second transducer; and

a processing circuit configured to implement:

a first adaptive filter associated with the first transducer;

a second adaptive filter associated with the second transducer; and a comparison block that compares the response of the first adaptive filter and the response of the second adaptive filter and determines based on the comparison whether a first headphone housing the first transducer is engaged with a first ear of a listener and the second headphone housing the second transducer is engaged with a second ear of the listener.

2. The integrated circuit of Claim 1 , wherein the processing circuit is further configured to, responsive to determining that at least one of first headphone is not engaged with the first ear and the second headphone is not engaged with the second ear, modify at least one of the first output signal and the second output signal such that at least one of the first output signal and the second output signal is different than such signal would be if the first headphone was engaged with the first ear and the second headphone was engaged with the second ear. 25

3. The integrated circuit of Claim 1, wherein:

the first adaptive filter comprises a first secondary path estimate adaptive filter for modeling an electro-acoustic path of a first source audio signal through the first transducer and having a response that generates a first secondary path estimate signal from the first source audio signal; and

the second adaptive filter comprises a second secondary path estimate adaptive filter for modeling an electro-acoustic path of a second source audio signal through the second transducer and having a response that generates a second secondary path estimate signal from the second source audio signal.

4. The integrated circuit of Claim 1, wherein modifying at least one of the first output signal and the second output signal comprises modifying the first output signal and the second output signal to be approximately equal to each other responsive to determining that either of the first headphone and the second headphone is not engaged with its respective ear.

5. The integrated circuit of Claim 4, wherein modifying the first output signal and the second output signal to be approximately equal to each other comprises calculating an average of a first source audio signal associated with the first output signal and a second source audio signal associated with the second output signal, and causing each of the first output signal and the second output signal to be approximately equal to the average.

6. The integrated circuit of Claim 1, wherein modifying at least one of the first output signal and the second output signal comprises increasing an audio volume of at least one of the first output signal and the second output signal responsive to determining that either of the first headphone and the second headphone is not engaged with its respective ear. 26

7. The integrated circuit of Claim 1, wherein modifying at least one of the first output signal and the second output signal comprises decreasing an audio volume of at least one of the first output signal and the second output signal responsive to determining that both of the first headphone and the second headphone are not engaged with their respective ears.

8. The integrated circuit of Claim 7, further comprising causing the personal audio device to enter a low-power mode responsive to determining that both of the first headphone and the second headphone are not engaged with their respective ears.

9. The integrated circuit of Claim 1, wherein modifying at least one of the first output signal and the second output signal comprises outputting a third output signal to a third transducer device responsive to determining that both of the first headphone and the second headphone are not engaged with their respective ears, wherein the third output signal is derivative of at least one of a first source audio signal associated with the first output signal and a second source audio signal associated with the second output signal.

10. The integrated circuit of Claim 1, wherein modifying at least one of the first output signal and the second output signal comprises allowing customized processing for each of the first output signal and the second output signal responsive to determining that either of the first headphone is engaged with the first ear and the second headphone is engaged with an ear of a second listener.

11. The integrated circuit of Claim 1 , further comprising:

an orientation detection signal input configured to receive an orientation detection signal indicative of an orientation of at least one of the first headphone and the second headphone relative to the earth; and

wherein the processing circuit is further configured to modify a video output signal comprising video image information for display to a display device of the personal audio device responsive to a change in orientation of at least one of the first headphone and the second headphone as indicated by the orientation detection signal. 27

12. The integrated circuit of Claim 11, wherein modifying the video output signal comprises rotation of an orientation of video image information displayed to the display device.

13. A method, comprising:

comparing a response of a first adaptive filter associated with a first transducer housed in a first earphone and a response of a second adaptive filter associated with a second transducer housed in a second earphone; and

determining based on the comparison whether the first headphone is engaged with the first ear and the second headphone is engaged with the second ear.

14. The method of Claim 13, further comprising, responsive to determining that at least one of the first headphone is not engaged with the first ear and the second headphone is not engaged with the second ear, modifying at least one of a first output signal to the first transducer and a second output signal to the second transducer such that at least one of the first output signal and the second output signal is different than such signal would be if the first headphone was engaged with the first ear and the second headphone was engaged with the second ear.

15. The method of Claim 13, wherein:

the first adaptive filter comprises a first secondary path estimate adaptive filter for modeling an electro-acoustic path of a first source audio signal through the first transducer and having a response that generates a first secondary path estimate signal from the first source audio signal; and

the second adaptive filter comprises a second secondary path estimate adaptive filter for modeling an electro-acoustic path of a second source audio signal through the second transducer and having a response that generates a second secondary path estimate signal from the second source audio signal. 28

16. The method of Claim 13, wherein modifying at least one of the first output signal and the second output signal comprises modifying the first output signal and the second output signal to be approximately equal to each other responsive to determining that either of the first headphone and the second headphone is not engaged with its respective ear.

17. The method of Claim 16, wherein modifying the first output signal and the second output signal to be approximately equal to each other comprises calculating an average of a first source audio signal associated with the first output signal and a second source audio signal associated with the second output signal, and causing each of the first output signal and the second output signal to be approximately equal to the average.

18. The method of Claim 13, wherein modifying at least one of the first output signal and the second output signal comprises increasing an audio volume of at least one of the first output signal and the second output signal responsive to determining that either of the first headphone and the second headphone is not engaged with its respective ear.

19. The method of Claim 13, wherein modifying at least one of the first output signal and the second output signal comprises decreasing an audio volume of at least one of the first output signal and the second output signal responsive to determining that both of the first headphone and the second headphone are not engaged with their respective ears. 20. The method of Claim 19, further comprising causing the personal audio device to enter a low-power mode responsive to determining that both of the first headphone and the second headphone are not engaged with their respective ears.

21. The method of Claim 13, wherein modifying at least one of the first output signal and the second output signal comprises outputting a third output signal to a third transducer device responsive to determining that both of the first headphone and the 29

second headphone are not engaged with their respective ears, wherein the third output signal is derivative of at least one of a first source audio signal associated with the first output signal and a second source audio signal associated with the second output signal. 22. The method of Claim 13, wherein modifying at least one of the first output signal and the second output signal comprises allowing customized processing for each of the first output signal and the second output signal responsive to determining that either of the first headphone is engaged with the first ear and the second headphone is engaged with an ear of a second listener.

23. The method of Claim 13, further comprising:

receiving an orientation detection signal indicative of an orientation of at least one of the first headphone and the second headphone relative to the earth; and

modifying a video output signal comprising video image information for display to a display device of the personal audio device responsive to a change in orientation of at least one of the first headphone and the second headphone as indicated by the orientation detection signal.

24. The method of Claim 23, wherein modifying the video output signal comprises rotation of an orientation of video image information displayed to the display device.

25. The method of Claim 15, wherein:

the first adaptive filter comprises a first feedforward adaptive filter that generates a first anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the first transducer; and

the second adaptive filter comprises a second feedforward adaptive filter that generates a second anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the second transducer. 30

26. The integrated circuit of Claim 3, wherein the processing circuit is further configured to implement:

a first coefficient control block that shapes the response of the first secondary path estimate adaptive filter in conformity with the first source audio signal and a first playback corrected error by adapting the response of the first secondary path estimate filter to minimize the first playback corrected error, wherein the first playback corrected error is based on a difference between a first error microphone signal and the first secondary path estimate signal; and

a second coefficient control block that shapes the response of the second secondary path estimate adaptive filter in conformity with the second source audio signal and a second playback corrected error by adapting the response of the second secondary path estimate filter to minimize the second playback corrected error, wherein the second playback corrected error is based on a difference between the second error microphone signal and the second secondary path estimate signal.

27. The integrated circuit of Claim 26, wherein the processing circuit further implements:

a first feedforward filter that generates a first anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the first transducer based at least on the first playback corrected error; and

a second feedforward filter that generates a second anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the second transducer based at least on the second playback corrected error. 28. The integrated circuit of Claim 1, wherein:

the first adaptive filter comprises a first feedforward adaptive filter that generates a first anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the first transducer; and

the second adaptive filter comprises a second feedforward adaptive filter that generates a second anti-noise signal to reduce a presence of ambient audio sounds at an acoustic output of the second transducer.