This page performs a discrete Fourier transform on real data and
plots
both the input waveform, the 'power' output, and the Fourier
synthesis.
Since the algorithm is
not based on a fast Fourier transform (FFT), the number of input
points
can be any value (i.e., it is not limited to a power of two), but
the
speed is much slower. The output includes a listing of the input as
a
check, and the sine and cosine components for the transform. The
'power' is calculated as the square root of the sum of the squares
of
the sine and cosine
component; these are the values plotted on the second graph. The
Fourier synthesis is a back calculation of the waveform using the
coefficients from the transform. Since the
listings are delimited with tab characters, they can readily be
exported into a spreadsheet.
Graphing uses the Canvas tag, which may not be available in some
older
browsers. The algorithm is in Javascript and can be viewed within
the
source of the page.
Jeffrey Clymer -- Debut July 4, 2011. Revision 3, July 9, 2011 --
Email
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