ref: 7ef285353e8a75f0709962e31f00bfc2dc1e88e6
dir: /src/FFT.h/
/*
*
* FFT.h
*
* Based on FFT.h from Audacity, which contained the following text:
*
* This file contains a few FFT routines, including a real-FFT
* routine that is almost twice as fast as a normal complex FFT,
* and a power spectrum routine when you know you don't care
* about phase information.
*
* Some of this code was based on a free implementation of an FFT
* by Don Cross, available on the web at:
*
* http://www.intersrv.com/~dcross/fft.html
*
* The basic algorithm for his code was based on Numerican Recipes
* in Fortran. I optimized his code further by reducing array
* accesses, caching the bit reversal table, and eliminating
* float-to-double conversions, and I added the routines to
* calculate a real FFT and a real power spectrum.
*
* Note: all of these routines use single-precision floats.
* I have found that in practice, floats work well until you
* get above 8192 samples. If you need to do a larger FFT,
* you need to use doubles.
*
* This file is now part of SoX, and is copyright Ian Turner and others.
*
* SoX is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* Foobar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with SoX; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef M_PI
#define M_PI 3.14159265358979323846 /* pi */
#endif
#ifdef __cplusplus
extern "C" {
#endif
/*
* This is the function you will use the most often.
* Given an array of floats, this will compute the power
* spectrum by doing a Real FFT and then computing the
* sum of the squares of the real and imaginary parts.
* Note that the output array is half the length of the
* input array, and that NumSamples must be a power of two.
*/
void PowerSpectrum(int NumSamples, float *In, float *Out);
/*
* Computes an FFT when the input data is real but you still
* want complex data as output. The output arrays are half
* the length of the input, and NumSamples must be a power of
* two.
*/
void RealFFT(int NumSamples,
float *RealIn, float *RealOut, float *ImagOut);
/*
* Computes a FFT of complex input and returns complex output.
* Currently this is the only function here that supports the
* inverse transform as well.
*/
void FFT(int NumSamples,
int InverseTransform,
float *RealIn, float *ImagIn, float *RealOut, float *ImagOut);
/*
* Applies a windowing function to the data in place
*/
typedef enum {RECTANGULAR = 0, /* no window */
BARTLETT = 1, /* triangular */
HAMMING = 2,
HANNING = 3} windowfunc_t;
void WindowFunc(windowfunc_t whichFunction, int NumSamples, float *data);
#ifdef __cplusplus
}
#endif