Michael Raiford <mra### [at] hotmailcom> wrote:
> Heh, as more come to me. I'm tossing together a little C# app to play
> around with the FFT and be able to examine it in both rectangular and
> polar forms.

Aha, I knew I had that lying around somewhere.  If you just want to play with
the behavior and not implement it yourself, there's always Matlab, or its free
equivalent, Octave.  Here's the simplest low-pass filter:

n=101; tmin=0; tmax=10;
%calculate time & frequency
  tbase = linspace(tmin,tmax,n);
  dt    = (tmax-tmin)/(n-1);
  ni    = floor((n-1)/2);
  fbase = [0:floor(n/2),ni:-1:1] /ni/2.0/dt;
%calculate y and fft(y)
  y = rand(size(tbase));
  Y = fft(y);
%filter
  Y_filt = Y;
  Y_filt(find(fbase>2.0)) = 0;
  y_filt = ifft(Y_filt);
%plot
  figure(1);  plot(tbase,y,tbase,y_filt);
  figure(2);  plot(fbase,abs(Y_filt));

 - Ricky

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