# US 2021/0280205 A1 · Methods and apparatus to reduce noise from harmonic noise sources > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0280205 A1 - Document ID: US20210280205A1 - Status: Published application - Kind: A1 - Application number: 17/328,984 - Filed: 2021-05-24 - Published: 2021-09-09 - Earliest claimed: 2017-10-26 - Assignees: The Nielsen Company (US), LLC - Applicants: The Nielsen Company (US), LLC - Inventors: Matthew McCallum - Web page: https://patentgrep.com/patent/US20210280205A1 ## CPC - G10L 21/0232: Processing in the frequency domain - G10L 19/018: Audio watermarking, i.e. embedding inaudible data in the audio signal - G10L 21/0264: characterised by the type of parameter measurement, e.g. correlation techniques, zero crossing techniques or predictive techniques - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract Methods, apparatus, systems and articles of manufacture are disclosed to reduce noise from harmonic noise sources. An example apparatus includes at least one memory; at least one processor 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. ## Claims ### Claim 1 An apparatus to reduce harmonic noise, the apparatus comprising: at least one memory; computer readable instructions; at least one processor 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. ### Claim 2 (depends on 1) 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. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the at least one processor is 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. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the at least one processor 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. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the at least one processor is to determine if the contour trace is an outlier based on a statistical distance from a parameter of the contour trace. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the at least one processor is to perform a short-time Fourier transform with a windowing length and an increment in samples between windows in the audio sample. ### Claim 7 (depends on 6) 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. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the at least one processor is to remove the contour trace from the audio sample when the amplitude values of the set of points satisfy an outlier threshold. ### Claim 9 A non-transitory computer readable storage medium comprising computer readable instructions which, when executed, cause a processor to: 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. ### Claim 10 (depends on 9) 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. ### Claim 11 (depends on 9) The non-transitory computer readable storage medium of claim 9, wherein the instructions, when executed, cause the processor 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. ### Claim 12 (depends on 9) The non-transitory computer readable storage medium of claim 9, wherein the instructions, when executed, 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. ### Claim 13 (depends on 9) The non-transitory computer readable storage medium of claim 9, wherein the instructions, when executed, cause the processor to determine if the contour trace is an outlier based on a statistical distance from a parameter of the contour trace. ### Claim 14 (depends on 9) The non-transitory computer readable storage medium of claim 9, wherein the instructions, when executed, cause the processor to perform a short-time Fourier transform with a windowing length and an increment in samples between windows in the audio sample. ### Claim 15 (depends on 14) 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. ### Claim 16 (depends on 9) The non-transitory computer readable storage medium of claim 9, wherein instructions, when executed, cause the processor is to remove the contour trace from the audio sample when the amplitude values of the set of points satisfy an outlier threshold. ### Claim 17 An apparatus to reduce harmonic noise, the apparatus comprising: means for generating a contour trace, the means for generating to: 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 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. ### Claim 18 (depends on 17) 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. ### Claim 19 (depends on 17) The apparatus of claim 17, wherein the means for generating the contour trace is 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. ### Claim 20 (depends on 17) The apparatus of claim 17, wherein the means for generating the contour trace 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. ### Claim 21 (depends on 17) 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. ### Claim 22 (depends on 17) The apparatus of claim 17, further including means for performing a short-time Fourier transform with a windowing length and an increment in samples between windows in the audio sample.