Method and apparatus for audio signal enhancement

1. A method for time-domain audio signal enhancement, the method comprising:

obtaining a first time-domain audio signal, M 1 , from a first physical microphone element;

obtaining a second time-domain audio signal, M 2 , from a second physical microphone element oriented differently than the first physical microphone element;

array processing the first time-domain audio signal and the second time-domain audio signal to generate a virtual linear first order element, M 1 -M 2 ;

array processing the first time-domain audio signal and the second time-domain audio signal to generate a virtual non-linear even order element, (M 1 -M 2 ) n , where n is an even number; and

combining the virtual linear first order element and the virtual non-linear even order element to generate a directional time-domain audio signal having a primary audio beam.

2. The method of claim 1 , wherein the virtual linear first order element is added to the virtual non-linear even order element to generate the directional time-domain audio signal.

3. The method of claim 2 , wherein array processing the first time-domain audio signal and the second time-domain audio signal to generate the virtual non-linear even order element comprises:

raising a first order bi-directional element to an even power.

4. The method of claim 3 , wherein the first order bi-directional element is a virtual first order bi-directional element created by:

taking a mathematical difference of the first time-domain audio signal and the second time-domain audio signal,

wherein the first physical microphone element is a first order directional element and the second physical microphone element is a first order directional element.

5. The method of claim 2 , wherein array processing the first time-domain audio signal and the second time-domain audio signal to generate the virtual linear first order element comprises:

linearly mixing a first order bi-directional element and an omnidirectional element.

6. The method of claim 5 , wherein the first order bi-directional element is a virtual first order bi-directional element created by:

taking a mathematical difference of the first time-domain audio signal and the second time-domain audio signal,

wherein the first physical microphone element is a first order directional element and the second physical microphone element is a first order directional element.

7. The method of claim 5 , wherein the omnidirectional element is a virtual omnidirectional element created by:

taking a mathematical sum of the first time-domain audio signal and the second time-domain audio signal,

wherein the first physical microphone element is a first order directional element and the second physical microphone element is a first order directional element.

8. The method of claim 1 , wherein the primary audio beam is oriented along a beam axis parallel with an orientation of at least the first physical microphone element.

9. The method of claim 1 , further comprising:

obtaining a third time-domain audio signal from a third physical microphone element; and

obtaining a fourth time-domain audio signal from a fourth physical microphone element,

wherein the first physical microphone element and the second physical microphone element are oriented parallel to a first axis, and the third physical microphone element and fourth physical microphone element are oriented parallel to a second axis, and wherein the first axis is orthogonal to the second axis.

10. The method of claim 9 , wherein the primary audio beam is oriented along a vector whose origin is at an intersection of the first axis and the second axis and whose tip can be steered through 360 degrees in a plane formed by the first axis and the second axis.

11. The method of claim 9 , further comprising:

obtaining a fifth time-domain audio signal from a fifth physical microphone element;

obtaining a sixth time-domain audio signal from a sixth physical microphone element;

wherein the fifth physical microphone element and sixth physical microphone element are oriented parallel to a third axis, and wherein the third axis is orthogonal to the first axis and the second axis.

12. The method of claim 11 , wherein the primary audio beam is oriented along a vector whose origin is at an intersection of the first axis, the second axis and the third axis, and whose tip can be steered through a sphere centered at the intersection of the first axis, the second axis and the third axis.

13. An apparatus for time-domain audio signal enhancement, comprising:

a first physical microphone element that is a first order directional element;

a second physical microphone element;

a first divider for scaling a time-domain audio signal, M 1 , from the first physical microphone element by a scaling factor to produce a first scaled time-domain audio signal;

a second divider for scaling a time-domain audio signal, M 2 , from the second physical microphone element by the scaling factor to produce a second scaled time-domain audio signal;

a processor for array processing the first scaled time-domain audio signal and the second scaled time-domain audio signal to generate

a virtual linear first order element, M 1 -M 2 , and

a virtual non-linear even order element, (M 1 -M 2 ) n , where n is an even number, and

combining the virtual linear first order element and the virtual non-linear even order element to generate a directional time-domain audio signal comprising a primary audio beam; and

a multiplier for multiplying the directional time-domain audio signal by the scaling factor.

14. The apparatus of claim 13 wherein the scaling factor is based on a magnitude of a largest time-domain audio signal from the first physical microphone element and the second physical microphone element.

15. The apparatus of claim 13 wherein the second physical microphone element is a first order directional element.

16. The apparatus of claim 13 wherein the second physical microphone element is an omnidirectional element.

17. The apparatus of claim 13 further comprising:

a first amplifier for calibrating gain of the first physical microphone element; and

a second amplifier for calibrating gain of the second physical microphone element.

18. The apparatus of claim 13 , wherein a distance separating the first physical microphone element and the second physical microphone element is less than one-half of a wavelength of a shortest wavelength of interest.

19. The apparatus of claim 13 , wherein the first physical microphone element and the second physical microphone element are oriented approximately in parallel to a first axis and at an angular separation of about 180 degrees to each other.

20. The apparatus of claim 19 , further comprising a third physical microphone element and a fourth physical microphone element oriented approximately in parallel to a second axis and at an angular separation of about 180 degrees to each other.

21. The apparatus of claim 20 , wherein the second axis is orthogonal to the first axis.

22. The apparatus of claim 20 , further comprising a fifth physical microphone element and a sixth physical microphone element oriented approximately in parallel to a third axis and at an angular separation of about 180 degrees to each other.

23. The apparatus of claim 22 , wherein the third axis is orthogonal to the first axis and the second axis.