Methods , apparatus , systems and articles of manufacture are
disclosed to reduce noise from harmonic noise sources . An
example apparatus includes a contour tracer to determine a
first point of comparatively large amplitude of a frequency
component in a frequency spectrum of an audio sample ,
determine a set of points in the frequency spectrum having
amplitude values within an amplitude threshold of the first
point , frequency values within a frequency threshold of the
first point , and phase values within a phase threshold of the
first point , increment a counter when a distance between ( 1 )
a second point in the set of points and ( 2 ) the first point
satisfies a distance threshold , and when the counter satisfies
a counter threshold , generate the contour trace , the contour
trace including the set of points , and a subtractor to remove
the contour trace from the audio sample when the amplitude
values satisfy an outlier threshold .
