# [chuck-users] Using FFT 'manually'

Kassen signal.automatique at gmail.com
Sun May 24 13:31:51 EDT 2009

```Fellow ChucKists,

Below I'm pasting a slight edit of this example;
http://chuck.cs.princeton.edu/doc/examples/analysis/win.ck

Note that my change involved editing out the upchuck and replacing it with a
transform on a array full of zero's. We'd expect that to result in silence.
Instead it sound exactly like the original example. I believe this means
that ,transform() is still looking to FFT's input instead of to the array
fed to it. In Siebe's case that meant silence as he didn't chuck a UGen into
his FFT.

I further tested this by feeding the input of FFT in Siebe's code with a
Noise UGen and indeed in that case the printout dutifully supplies us with a
train of numbers.

So, yes, that's a bug, probably a typo on .transform()'s code which seems to
be taking the wrong array.

Yours,
Kas.

========demo code follows==============
// our patch
SinOsc g => FFT fft => blackhole;
// synthesis
IFFT ifft => dac;
// set srate
second / samp => float srate;

// set parameters
1024 => fft.size;
// window
Windowing.hamming(512) => fft.window;
Windowing.hamming(512) => ifft.window;

// use this to hold contents
complex s[fft.size()/2];
// divide
int div;

float foo[fft.size()]; //note this is a array holding just zero's and will
stay that way

// control loop
while( true )
{
// set freq
srate / fft.size() * div++ => g.freq;
fft.size()/2 %=> div;

// take fft
//fft.upchuck();               //commented out by Kas

fft.transform(foo);        //added by Kas

// get contents
fft.spectrum( s );
// take ifft
ifft.transform( s );