[nSLUG] Possibly ignorant quest for simple FFT app
Mike Spencer
mspencer at tallships.ca
Thu Jul 11 03:44:03 ADT 2013
Summary: Looking for Fourier software simpleminded enough for me to be
able to use it.
I have a basic, possibly horribly distorted, idea of what a Fourier
transform does: You can make believe that:
+ any list of numbers are the amplitudes of one cycle of a
hypothetical periodic function for even-spaced values of t,
or that
+ any list of pairs of numbers are the t/amplitude values for
one cycle of a hypothetical periodic function.
And Fourier's insight says that any periodic function can be
represented as an infinite series of sums, vaguely like:
inf
SIGMA A sin(nt) + B cos(nt) [where A & B are subscripted with n]
n=1
Yeah... [1]
I'd like a simple command line program that will take an arbitrary
array of numbers or x/y number pairs and return the A & B coefficients
up to some modest max value for n.
What I find on the net is one of:
+ FFT libraries for which I have to write surrounding code.
+ Interactive apps for serious DSP guys.
+ Apps for serious math weenies.
all of which seem to start out assuming I know waayyy more than I do
(viz. very little) about the subject and don't promise to give me the
simple results sought.
Purpose is to look for frequency patterns (if any) in putative random
numbers and also -- even more frivolously -- in the recordings made
from the mouse exercise-wheel tachometer. [2]
I recall seeing graphic rendering of data from (what I took to be)
such a Fourier program on the screen of a guy who was doing hard-core
random number research for crypto. I've lost track of him.
Maybe I'm so ignorant in this area that this is all too misguided for
a meaningful reply. In that case you can just treat this as idle
entertainment on a slow day for the NSLUG list.
- Mike
[1] ...the real equation with discussion is in my old calculus
textbook. I'm weak on math and it doesn't get better with age.
Not looking for a tutorial on Fourier math or FFT code.
[2] Our mouse slacked off all winter but resumed using the wheel in
the spring and I've logged over 30 evenings of running. Record is
16,000+ turns of the wheel or about 4.8 miles in one evening.
Visualizing the data requires an image 480x24000 pixels which
gnuplot does nery nicely. :-)
--
Michael Spencer Nova Scotia, Canada .~.
/V\
mspencer at tallships.ca /( )\
http://home.tallships.ca/mspencer/ ^^-^^
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