66 lines
2.2 KiB
C
66 lines
2.2 KiB
C
/**********************************************************************
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FFT.h
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Dominic Mazzoni
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September 2000
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This file contains a few FFT routines, including a real-FFT
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routine that is almost twice as fast as a normal complex FFT,
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and a power spectrum routine which is more convenient when
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you know you don't care about phase information. It now also
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contains a few basic windowing functions.
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Some of this code was based on a free implementation of an FFT
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by Don Cross, available on the web at:
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http://www.intersrv.com/~dcross/fft.html
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The basic algorithm for his code was based on Numerical Recipes
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in Fortran. I optimized his code further by reducing array
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accesses, caching the bit reversal table, and eliminating
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float-to-double conversions, and I added the routines to
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calculate a real FFT and a real power spectrum.
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Note: all of these routines use single-precision floats.
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I have found that in practice, floats work well until you
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get above 8192 samples. If you need to do a larger FFT,
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you need to use doubles.
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**********************************************************************/
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/*
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* This is the function you will use the most often.
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* Given an array of floats, this will compute the power
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* spectrum by doing a Real FFT and then computing the
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* sum of the squares of the real and imaginary parts.
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* Note that the output array is half the length of the
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* input array, and that NumSamples must be a power of two.
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*/
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void PowerSpectrum(int NumSamples, float *In, float *Out);
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/*
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* Computes an FFT when the input data is real but you still
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* want complex data as output. The output arrays are the
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* same length as the input, but will be conjugate-symmetric
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* NumSamples must be a power of two.
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*/
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void RealFFT(int NumSamples,
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float *RealIn, float *RealOut, float *ImagOut);
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/*
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* Computes an Inverse FFT when the input data is conjugate symmetric
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* so the output is purely real. NumSamples must be a power of
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* two.
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* Requires: EXPERIMENTAL_USE_REALFFTF
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*/
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void InverseRealFFT(int NumSamples,
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float *RealIn, float *ImagIn, float *RealOut);
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void RealInverseRealFFT(int NumSamples, float *In, float *Out);
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void DeinitFFT();
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