Methods and apparatus to reduce noise from harmonic noise sources
View Patent ↗Methods, apparatus, systems and articles of manufacture are disclosed to reduce noise from harmonic noise sources. Example methods disclosed herein include determining a point of comparatively large amplitude for a frequency in an audio sample, generating a contour trace beginning at the point, and calculating a parameter for the contour trace. The example method includes, in response to the contour trace being an outlier based on the parameter, removing the contour trace from the audio sample.
1. An apparatus to reduce harmonic noise, the apparatus comprising:
a contour tracer to:
determine a point of comparatively large amplitude for a frequency in an audio sample; and
generate a contour trace beginning at the point, the contour trace including other points having (1) amplitude values within an amplitude threshold from the point or another one of the other points, (2) frequency values within a frequency threshold from the point or another one of the other points, and (3) phase values within a phase threshold from the point or another one of the other points:
a parameter calculator to calculate a parameter for the contour trace; and
a subtractor to, in response to the contour trace being an outlier based on the parameter, remove the contour trace from the audio sample.
2. The apparatus of claim 1 , wherein the contour tracer is to generate the contour trace by stepping forward and backward in time from the point, the contour trace to terminate when a skipped frame threshold is satisfied, the skipped frame threshold corresponding to a maximum number of successive time 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.
3. The apparatus of claim 1 , wherein the contour tracer is 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.
4. The apparatus of claim 1 , further including a classifier to determine if the contour trace is the outlier based on a statistical distance from the parameter.
5. The apparatus of claim 1 , wherein removal of the contour trace results in a noise-reduced audio signal that is used to generate an accurate audio signature.
6. The apparatus of claim 1 , further including a domain converter to perform a short-time Fourier transform with a specified windowing length and window time frame on the audio sample.
7. The apparatus of claim 6 , wherein the points of the contour trace occur in succession within a skipped frame threshold of one another or the point.
8. A computer readable storage medium comprising computer readable instructions which, when executed, cause a processor to:
determine a point of comparatively large amplitude for a frequency in an audio sample;
generate a contour trace beginning at the point, the contour trace including other points having (1) amplitude values within an amplitude threshold from the point or another one of the other points, (2) frequency values within a frequency threshold from the point or another one of the other points, and (3) phase values within a phase threshold from the point or another one of the other points;
calculate a parameter for the contour trace; and
in response to the contour trace being an outlier based on the parameter, remove the contour trace from the audio sample.
9. The computer readable storage medium of claim 8 , wherein the instructions, when executed, further cause the processor to generate the contour trace by stepping forward and backward in time from the point, the contour trace to terminate when a skipped frame threshold is satisfied, the skipped frame threshold corresponding to a maximum number of successive time 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.
10. The computer readable storage medium of claim 8 , wherein the instructions, when executed, further cause the processor 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.
11. The computer readable storage medium of claim 8 , wherein the instructions, when executed, further cause the processor to determine if the contour trace is the outlier based on a statistical distance from the parameter.
12. The computer readable storage medium of claim 8 , wherein removal of the contour trace results in a noise-reduced audio signal that is used to generate an accurate audio signature.
13. The computer readable storage medium of claim 8 , wherein the instructions, when executed, further cause the processor to perform a short-time Fourier transform with a specified windowing length and window time frame on the audio sample.
14. The computer readable storage medium of claim 8 , wherein the points of the contour trace occur in succession within a skipped frame threshold of one another or the point.
15. A method comprising:
determining a point of comparatively large amplitude for a frequency in an audio sample;
generating a contour trace beginning at the point, the contour trace including other points having (1) amplitude values within an amplitude threshold from the point or another one of the other points, (2) frequency values within a frequency threshold from the point or another one of the other points, and (3) phase values within a phase threshold from the point or another one of the other points;
calculating a parameter for the contour trace; and
in response to the contour trace being an outlier based on the parameter, removing the contour trace from the audio sample.
16. The method of claim 15 , wherein generating the contour trace includes stepping forward and backward in time from the point, the contour trace to terminate when a skipped frame threshold is satisfied, the skipped frame threshold corresponding to a maximum number of successive time 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.
17. The method of claim 15 , further including determining points of comparatively large amplitude for a representative number of frequencies in the audio sample and generating contours for a specified percentage of the points of comparatively large amplitude in the audio sample.
18. The method of claim 15 , further including determining if the contour trace is the outlier based on a statistical distance from the parameters.
19. The method of claim 15 , wherein removal of the contour trace results in a noise-reduced audio signal that is used to generate an accurate audio signature.
20. The method of claim 15 , further including performing a short-time Fourier transform with a specified windowing length and window time frame on the audio sample.