[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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