Method and System for Contact Sensing Using Coherence Analysis

1. A method for acoustical switching suitable for use with a microphone enabled electronic device, the method comprising the steps of: capturing a first microphone signal from a first microphone on a device; by way of a processor on, in or operatively coupled to, the device communicatively coupled to the first microphone: analyzing the first microphone signal for a contact event versus a non-contact event; directing the electronic device to switch a processing state responsive to a detection of either the contact event or non-contact event, capturing a second microphone signal from a second microphone on the device; by way of the processor communicatively coupled to the first microphone and communicatively coupled to the second microphone: performing a coherence function on the first microphone signal and the second microphone signal; generating a smoothed coherence function from the coherence function; resolving a peak in the smoothed coherence function; comparing the peak in the smoothed coherence function to a threshold; and deciding the physical contact has occurred if the peak is greater than the threshold.

2. The method of claim 1 , wherein the processing state responsive to detecting the contact event comprises at least one of performing a user interface action, a command response, an automatic interaction or a recording.

3. The method of claim 1 , wherein the processing state responsive to detecting the non-contact event comprises at least one of performing a voice communication, a data communication, an event detection, a speech recognition, a key word detection, or an SPL measurement.

4. The method of claim 1 configured for contact sensing suitable for use with the microphone enabled electronic device, further comprising the steps of: analyzing the coherence function to determine if a physical contact due to touch occurred on the device.

5. The method of claim 4 , further comprising discriminating between the physical contact with a high inter-microphone coherence and an airborne event with a low inter-microphone coherence.

6. The method of claim 4 , further comprising providing a change to at least one parameter setting on the electronic device responsive to determining the physical contact occurred, wherein the first microphone and the second microphone are acoustical-mechanically coupled together on the electronic device.

7. The method of claim 6 , further comprising resolving one or more peaks in the coherence function; evaluating a time window between the one or more peaks; setting a contact detection status to a negative value for de-bouncing if the time window is less than a previous time window, otherwise setting the contact detection status to a positive value.

8. The method of claim 7 , further comprising counting a number of the contact detection status events for positive values; and differentiating between a single tap and a double tap from analysis of the contact detection status if the number is within a time period.

9. The method of claim 4 , wherein the coherence function is a function of the power spectral densities, Pxx(f) and Pyy(f), of x and y, and the cross power spectral density, Pxy(f), of x and y, as: C x ⁢ ⁢ y ⁡ ( f ) =  P x ⁢ ⁢ y ⁡ ( f )  2 P x ⁢ ⁢ x ⁡ ( f ) ⁢ P y ⁢ ⁢ y ⁡ ( f ) ⁢ .

10. The method of claim 4 , wherein a length of power spectral densities and a cross power spectral density of the coherence function are within 2 to 5 milliseconds.

11. The method of claim 4 , wherein a time-smoothing parameter for updating power spectral densities and a cross power spectral density is within 0.2 to 0.5 seconds.

12. The method of claim 4 , further comprising: tuning a cavitational acoustic resonance by way of resonant air channels; and reducing sensitivity of the coherence function to an airborne event from the tuned cavitational acoustic resonance of the first and second microphone signals.

13. The method of claim 12 , further comprising producing a spectral notch specific to the airborne sound event by shaping the resonant air channel to decrease the coherence function for the airborne sound in a frequency band of interest.

14. A system for acoustical switching suitable for use with a microphone enabled electronic device, the system comprising: a first microphone on or in the device for capturing a first microphone signal; an acoustic switch communicatively coupled to the first microphone; a second microphone for capturing a second microphone signal, and the processor communicatively coupled to the first microphone and the second microphone, the processor configured for: analyzing the first microphone signal for a contact event versus a non-contact event; directing the electronic device to switch a processing state responsive to a detection of either the contact event or non-contact event; performing a coherence function on the first microphone signal and the second microphone signal; generating a smoothed coherence function from the coherence function; resolving a peak in the smoothed coherence function; comparing the peak in the smoothed coherence function to a threshold; and deciding the physical contact has occurred if the peak is greater than the threshold.

15. The system of claim 14 , wherein the processing state, by way of a processor on, or operatively coupled to the device, responsive to detecting the contact event comprises at least one of performing a user interface action, a command response, an automatic interaction or a recording.

16. The system of claim 14 , wherein the processing state, by way of a processor on, or operatively coupled to the device, responsive to detecting the non-contact event comprises at least one of a voice communication, a data communication, an event detection, a speech recognition or a key word detection.

17. The system of claim 14 configured for contact sensing on a device, the processor further configured for: analyzing the coherence function to determine if a physical contact due to touch occurred on the device.

18. The system of claim 17 , wherein the processor discriminates between the physical contact with a high inter-microphone coherence and an airborne event with a low inter-microphone coherence.

19. The system of claim 17 , wherein the processor performs the steps of: providing a user interface command to the device responsive to determining the physical contact occurred, wherein the first microphone and the second microphone are acoustical-mechanically coupled together on the device.

20. The system of claim 17 , wherein the processor performs the steps of: resolving one or more peaks in the coherence function; evaluating a time window between the one or more peaks; setting a contact detection status to a negative value for de-bouncing if the time window is less than a previous time window, otherwise setting the contact detection status to a positive value.

21. The system of claim 19 , wherein the processor performs the steps of: counting a number of the contact detection status events for positive values; and differentiating between a single tap and a double tap from analysis of the contact detection status if the number is within a time period.

22. The system of claim 19 , wherein the processor generates a coherence as a function of the power spectral densities, Pxx(f) and Pyy(f), of x and y, and the cross power spectral density, Pxy(f), of x and y, as: C x ⁢ ⁢ y ⁡ ( f ) =  P x ⁢ ⁢ y ⁡ ( f )  2 P x ⁢ ⁢ x ⁡ ( f ) ⁢ P y ⁢ ⁢ y ⁡ ( f ) ⁢ .

23. The system of claim 19 , further comprising: a first acoustic cavity above the first microphone to create a first resonant air channel; a second acoustic cavity above the second microphone to create a second resonant air channel; wherein the processor performs the steps of tunes an acoustic resonance of the first and second microphone signals by way of the first and second resonant air channels; and reduces a sensitivity of the coherence function to an airborne sound event from the tuned cavitational acoustic resonance of the first and second microphone signals.

24. The system of claim 22 , wherein the shaping of the first and second resonant air channels decreases the coherence function in a frequency band of interest and produces a spectral notch specific to the airborne event to reduce false positives.