[Stk] any FFT available on STK

[Craig Sapp]

Hello Josep,

2008/4/14 Josep Comajuncosas <josep.comajuncosas at gmail.com>:

> Hi,
> well just this, does anyone have a nice working example of an FFT library
> implemented in the stk framework?
> Thanks in advance
> Josep M
>

Not quite what you want, but close: I have a C++ interface for FFTW
(http://www.fftw.org) which is probably the most efficient FFT library
available for free.

Here is my C++ interface class to FFTW:
    http://sv.mazurka.org.uk/src/MazurkaTransformer.cpp
    http://sv.mazurka.org.uk/include/MazurkaTransformer.h
which I use to make vamp plugins for the Sonic Visualiser
audio editor (http://www.sonicvisualiser.org).

The MazurkaTransformer::initialize function demonstrates the
setup requried for running the FFTW transform, and the function
doTransform() does the actual work of calculating the transform
using FFTW's function called fftw_execute().

Example usage:

////////////////////////////////
#include "MazurkaTransformer.h"
#include <iostream>
#include <iomanip>
#include <math.h>
#define SIZE 32
using namespace std;

int main(void) {
   MazurkaTransformer bumblebee;
   bumblebee.setSize(SIZE);

   int i;
   double signal[SIZE];
   double window[SIZE];

   for (i=0; i<SIZE; i++) {
      signal[i] = sin(2.0 * M_PI * 5 * i / SIZE);  // putting energy in bin
5
      window[i] = 0.5 - 0.5 * cos(2.0 * M_PI * i / SIZE); // Hann window
   }

   for (i=0; i<SIZE; i++) {
      bumblebee.signalNonCausal(i) = signal[i] * window[i];
   }

   bumblebee.doTransform();

   for (i=0; i<SIZE; i++) {
      cout << "bin " << i << ":"
           << setiosflags(ios::fixed)
           << setprecision(3)
           << "\treal= " << setw(7) << bumblebee.getSpectrum(i).re
           << "\timag= " << setw(7) << bumblebee.getSpectrum(i).im
           << "\tmag= "  << setw(7) << bumblebee.getSpectrumMagnitude(i)
           << "\n";
   }

   return 0;
}

/* compiling example:
    g++ -Iinclude MazurkaTransformer.cpp test.cpp -Lfftw/lib -lfftw3 -o test
*/

/////////////////////////////////

Which produces the following printout (bin 0 = 0 Hz, bins 1-15 are the
positive frequencies):

bin 0:  real=  -0.000   imag=   0.000   mag=   0.000
bin 1:  real=  -0.000   imag=   0.000   mag=   0.000
bin 2:  real=   0.000   imag=  -0.000   mag=   0.000
bin 3:  real=   0.000   imag=  -0.000   mag=   0.000
bin 4:  real=   0.000   imag=   4.000   mag=   4.000
bin 5:  real=   0.000   imag=   8.000   mag=   8.000
bin 6:  real=   0.000   imag=   4.000   mag=   4.000
bin 7:  real=   0.000   imag=   0.000   mag=   0.000
bin 8:  real=   0.000   imag=   0.000   mag=   0.000
bin 9:  real=  -0.000   imag=  -0.000   mag=   0.000
bin 10: real=  -0.000   imag=  -0.000   mag=   0.000
bin 11: real=  -0.000   imag=   0.000   mag=   0.000
bin 12: real=   0.000   imag=  -0.000   mag=   0.000
bin 13: real=  -0.000   imag=  -0.000   mag=   0.000
bin 14: real=  -0.000   imag=   0.000   mag=   0.000
bin 15: real=   0.000   imag=   0.000   mag=   0.000
bin 16: real=  -0.000   imag=   0.000   mag=   0.000
bin 17: real=   0.000   imag=  -0.000   mag=   0.000
bin 18: real=  -0.000   imag=  -0.000   mag=   0.000
bin 19: real=  -0.000   imag=   0.000   mag=   0.000
bin 20: real=   0.000   imag=   0.000   mag=   0.000
bin 21: real=  -0.000   imag=  -0.000   mag=   0.000
bin 22: real=  -0.000   imag=   0.000   mag=   0.000
bin 23: real=  -0.000   imag=   0.000   mag=   0.000
bin 24: real=   0.000   imag=  -0.000   mag=   0.000
bin 25: real=   0.000   imag=  -0.000   mag=   0.000
bin 26: real=   0.000   imag=  -4.000   mag=   4.000
bin 27: real=   0.000   imag=  -8.000   mag=   8.000
bin 28: real=   0.000   imag=  -4.000   mag=   4.000
bin 29: real=   0.000   imag=   0.000   mag=   0.000
bin 30: real=   0.000   imag=   0.000   mag=   0.000
bin 31: real=  -0.000   imag=  -0.000   mag=   0.000

-=+Craig
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