Method and apparatus for audio signal enhancement

• US 8,873,768 B2
• Filed: 12/23/2004
• Issued: 10/28/2014
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola Mobility LLC (Lenovo Group Ltd.)
• Inventors: Zurek, Robert A.
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): BLAIR, KILE O
• Application Number:
  US11/021,350
• Publication Number:
  US 20060140417A1
• Time in Patent Office: 3,596 Days
• Field of Search: 381/91, 381/92, 381/95, 381/111, 381/113, 381/122, 381/356
• US Class Current: 381/92
• CPC Class Codes: H04R 2201/401 2D or 3D arrays of transducers
• CPC Class Codes: H04R 2410/01 Noise reduction using microphones having different directional characteristics
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A method for audio signal enhancement comprising obtaining (222) a first audio signal from a first physical microphone element and obtaining a second audio signal from a second physical microphone element. The audio signals are array processed (226) to generate a virtual linear first order element and a virtual non-linear even order element. The array processing (226) includes combining the virtual linear first order element and the virtual non-linear even order element to generate a directional audio signal having a primary audio beam. An apparatus is disclosed for implementing the method.

Claims

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

obtaining a first time-domain audio signal, M₁, from a first physical microphone element;

obtaining a second time-domain audio signal, M₂, 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, M₁-M₂;

array processing the first time-domain audio signal and the second time-domain audio signal to generate a virtual non-linear even order element, (M₁-M₂)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, M₁, 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, M₂, 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, M₁-M₂, and

a virtual non-linear even order element, (M₁-M₂)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.