Methods and apparatus to reduce noise from harmonic noise sources

1. An apparatus to reduce harmonic noise, the apparatus comprising:

at least one memory;

computer readable instructions in the apparatus; and

processor circuitry to execute the computer readable instructions to at least:

determine a first amplitude value of a frequency component in a frequency spectrum of an audio sample;

determine a set of points in the frequency spectrum having at least one of (a) amplitude values within an amplitude threshold of the first amplitude value, (b) frequency values within a frequency threshold of the first amplitude value, or (c) phase values within a phase threshold of the first amplitude value;

increment a counter when a distance between (1) a second amplitude value in the set of points and (2) the first amplitude value satisfies a distance threshold; and

when the counter satisfies a counter threshold, generate a contour trace based on the set of points.

2. The apparatus of claim 1 , wherein the distance threshold is satisfied when a complex distance between the first amplitude value and the second amplitude value is less than the distance threshold.

3. The apparatus of claim 1 , wherein the at processor circuitry generates the contour trace by stepping forward and backward in time from the first amplitude value, the contour trace to terminate when the counter threshold is satisfied, the counter threshold corresponding to a maximum number of successive frames during which a point is not found with amplitude satisfying the amplitude threshold, frequency satisfying the frequency threshold, and phase satisfying the phase threshold relative to another point of the contour trace.

4. The apparatus of claim 1 , wherein the processor circuitry further executes the computer readable instructions to at least determine points of comparatively large amplitude for a representative number of frequencies in the audio sample and to generate contours for a specified percentage of the points of comparatively large amplitude in the audio sample.

5. The apparatus of claim 1 , wherein the processor circuitry further executes the computer readable instructions to at least determine if the contour trace is an outlier based on a statistical distance from a parameter of the contour trace.

6. The apparatus of claim 1 , wherein the processor circuitry further executes the computer readable instructions to at least perform a short-time Fourier transform with a windowing length and an increment in samples between windows in the audio sample.

7. The apparatus of claim 6 , wherein the set of points of the contour trace occur in succession within the distance threshold of one another or the first amplitude value.

8. The apparatus of claim 1 , wherein the processor circuitry further executes the computer readable instructions to at least remove the contour trace from the audio sample when the amplitude values of the set of points satisfy an outlier threshold.

9. A non-transitory computer readable storage medium comprising computer readable instructions which, when executed, cause one or more processors to at least:

determine a first amplitude value of a frequency component in a frequency spectrum of an audio sample;

determine a set of points in the frequency spectrum having at least one of (a) amplitude values within an amplitude threshold of the first amplitude value, (b) frequency values within a frequency threshold of the first amplitude value, or (c) phase values within a phase threshold of the first amplitude value;

increment a counter when a distance between (1) a second amplitude value in the set of points and (2) the first amplitude value satisfies a distance threshold; and

when the counter satisfies a counter threshold, generate a contour trace based on the set of points.

10. The non-transitory computer readable storage medium of claim 9 , wherein the distance threshold is satisfied when a complex distance between the first amplitude value and the second amplitude value is less than the distance threshold.

11. The non-transitory computer readable storage medium of claim 9 , wherein the instructions, when executed, cause the one or more processors to generate the contour trace by stepping forward and backward in time from the first amplitude value, the contour trace to terminate when the counter threshold is satisfied, the counter threshold corresponding to a maximum number of successive frames during which a point is not found with amplitude satisfying the amplitude threshold, frequency satisfying the frequency threshold, and phase satisfying the phase threshold relative to another point of the contour trace.

12. The non-transitory computer readable storage medium of claim 9 , wherein the instructions, when executed, cause the one or more processors to determine points of comparatively large amplitude for a representative number of frequencies in the audio sample and to generate contours for a specified percentage of the points of comparatively large amplitude in the audio sample.

13. The non-transitory computer readable storage medium of claim 9 , wherein the instructions, when executed, cause the one or more processors to determine if the contour trace is an outlier based on a statistical distance from a parameter of the contour trace.

14. The non-transitory computer readable storage medium of claim 9 , wherein the instructions, when executed, cause the one or more processors to perform a short-time Fourier transform with a windowing length and an increment in samples between windows in the audio sample.

15. The non-transitory computer readable storage medium of claim 14 , wherein the set of points of the contour trace occur in succession within the distance threshold of one another or the first amplitude value.

16. The non-transitory computer readable storage medium of claim 9 , wherein instructions, when executed, cause the one or more processors to remove the contour trace from the audio sample when the amplitude values of the set of points satisfy an outlier threshold.

17. An apparatus to reduce harmonic noise, the apparatus comprising:

means for generating a contour trace, the means for generating comprising, at least:

determining a first amplitude value of a frequency component in a frequency spectrum of an audio sample;

determining a set of points in the frequency spectrum having at least one of (a) amplitude values within an amplitude threshold of the first amplitude value, (b) frequency values within a frequency threshold of the first amplitude value, or (c) phase values within a phase threshold of the first amplitude value;

incrementing a counter when a distance between (1) a second amplitude value in the set of points and (2) the first amplitude value satisfies a distance threshold; and

when the counter satisfies a counter threshold, generating the contour trace based on the set of points; and

means for removing the contour trace from the audio sample when the amplitude values of the set of points satisfy a threshold.

18. The apparatus of claim 17 , wherein the distance threshold is satisfied when a complex distance between the first amplitude value and the second amplitude value is less than the distance threshold.

19. The apparatus of claim 17 , wherein the means for generating the contour trace further comprising, at least, generating the contour trace by stepping forward and backward in time from the first amplitude value, the contour trace to terminate when the counter threshold is satisfied, the counter threshold corresponding to a maximum number of successive frames during which a point is not found with amplitude satisfying the amplitude threshold, frequency satisfying the frequency threshold, and phase satisfying the phase threshold relative to another point of the contour trace.

20. The apparatus of claim 17 , wherein the means for generating the contour trace further comprising, at least, determining points of comparatively large amplitude for a representative number of frequencies in the audio sample and to generating contours for a specified percentage of the points of comparatively large amplitude in the audio sample.

21. The apparatus of claim 17 , further including means for determining if the contour trace is an outlier based on a statistical distance from a parameter of the contour trace.