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diff --git a/media/kiss_fft/README b/media/kiss_fft/README deleted file mode 100644 index 03b2e7a9c1..0000000000 --- a/media/kiss_fft/README +++ /dev/null @@ -1,134 +0,0 @@ -KISS FFT - A mixed-radix Fast Fourier Transform based up on the principle, -"Keep It Simple, Stupid." - - There are many great fft libraries already around. Kiss FFT is not trying -to be better than any of them. It only attempts to be a reasonably efficient, -moderately useful FFT that can use fixed or floating data types and can be -incorporated into someone's C program in a few minutes with trivial licensing. - -USAGE: - - The basic usage for 1-d complex FFT is: - - #include "kiss_fft.h" - - kiss_fft_cfg cfg = kiss_fft_alloc( nfft ,is_inverse_fft ,0,0 ); - - while ... - - ... // put kth sample in cx_in[k].r and cx_in[k].i - - kiss_fft( cfg , cx_in , cx_out ); - - ... // transformed. DC is in cx_out[0].r and cx_out[0].i - - free(cfg); - - Note: frequency-domain data is stored from dc up to 2pi. - so cx_out[0] is the dc bin of the FFT - and cx_out[nfft/2] is the Nyquist bin (if exists) - - Declarations are in "kiss_fft.h", along with a brief description of the -functions you'll need to use. - -Code definitions for 1d complex FFTs are in kiss_fft.c. - -You can do other cool stuff with the extras you'll find in tools/ - - * multi-dimensional FFTs - * real-optimized FFTs (returns the positive half-spectrum: (nfft/2+1) complex frequency bins) - * fast convolution FIR filtering (not available for fixed point) - * spectrum image creation - -The core fft and most tools/ code can be compiled to use float, double, - Q15 short or Q31 samples. The default is float. - - -BACKGROUND: - - I started coding this because I couldn't find a fixed point FFT that didn't -use assembly code. I started with floating point numbers so I could get the -theory straight before working on fixed point issues. In the end, I had a -little bit of code that could be recompiled easily to do ffts with short, float -or double (other types should be easy too). - - Once I got my FFT working, I was curious about the speed compared to -a well respected and highly optimized fft library. I don't want to criticize -this great library, so let's call it FFT_BRANDX. -During this process, I learned: - - 1. FFT_BRANDX has more than 100K lines of code. The core of kiss_fft is about 500 lines (cpx 1-d). - 2. It took me an embarrassingly long time to get FFT_BRANDX working. - 3. A simple program using FFT_BRANDX is 522KB. A similar program using kiss_fft is 18KB (without optimizing for size). - 4. FFT_BRANDX is roughly twice as fast as KISS FFT in default mode. - - It is wonderful that free, highly optimized libraries like FFT_BRANDX exist. -But such libraries carry a huge burden of complexity necessary to extract every -last bit of performance. - - Sometimes simpler is better, even if it's not better. - -FREQUENTLY ASKED QUESTIONS: - Q: Can I use kissfft in a project with a ___ license? - A: Yes. See LICENSE below. - - Q: Why don't I get the output I expect? - A: The two most common causes of this are - 1) scaling : is there a constant multiplier between what you got and what you want? - 2) mixed build environment -- all code must be compiled with same preprocessor - definitions for FIXED_POINT and kiss_fft_scalar - - Q: Will you write/debug my code for me? - A: Probably not unless you pay me. I am happy to answer pointed and topical questions, but - I may refer you to a book, a forum, or some other resource. - - -PERFORMANCE: - (on Athlon XP 2100+, with gcc 2.96, float data type) - - Kiss performed 10000 1024-pt cpx ffts in .63 s of cpu time. - For comparison, it took md5sum twice as long to process the same amount of data. - - Transforming 5 minutes of CD quality audio takes less than a second (nfft=1024). - -DO NOT: - ... use Kiss if you need the Fastest Fourier Transform in the World - ... ask me to add features that will bloat the code - -UNDER THE HOOD: - - Kiss FFT uses a time decimation, mixed-radix, out-of-place FFT. If you give it an input buffer - and output buffer that are the same, a temporary buffer will be created to hold the data. - - No static data is used. The core routines of kiss_fft are thread-safe (but not all of the tools directory). - - No scaling is done for the floating point version (for speed). - Scaling is done both ways for the fixed-point version (for overflow prevention). - - Optimized butterflies are used for factors 2,3,4, and 5. - - The real (i.e. not complex) optimization code only works for even length ffts. It does two half-length - FFTs in parallel (packed into real&imag), and then combines them via twiddling. The result is - nfft/2+1 complex frequency bins from DC to Nyquist. If you don't know what this means, search the web. - - The fast convolution filtering uses the overlap-scrap method, slightly - modified to put the scrap at the tail. - -LICENSE: - Revised BSD License, see COPYING for verbiage. - Basically, "free to use&change, give credit where due, no guarantees" - Note this license is compatible with GPL at one end of the spectrum and closed, commercial software at - the other end. See http://www.fsf.org/licensing/licenses - - A commercial license is available which removes the requirement for attribution. Contact me for details. - - -TODO: - *) Add real optimization for odd length FFTs - *) Document/revisit the input/output fft scaling - *) Make doc describing the overlap (tail) scrap fast convolution filtering in kiss_fastfir.c - *) Test all the ./tools/ code with fixed point (kiss_fastfir.c doesn't work, maybe others) - -AUTHOR: - Mark Borgerding - Mark@Borgerding.net |