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Not clear on FFTW license requirements
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August 26, 2020 - 1:00 pm
Member Since: August 26, 2020
Forum Posts: 1
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Many developers, it seems, are downloading and using FFTW in their projects but I'm not sure the license requirements are clear.  FFTW license info seems to indicate that any product that uses the "free" version of FFTW must be released as open source.

Do I misunderstand?  I don't see any of the major developers - who I'm sure use FFTW - releasing their plugins as open source nor do I expect they paid $10,000 for a commercial license.

Will P. - the examples in your book require FFTW - can you advise please?

Thank you.

October 20, 2020 - 5:01 pm
Member Since: January 29, 2017
Forum Posts: 689
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You are correct. FFTW has serious licensing dependencies and is somewhat draconian regarding use. 

However, it is very well known and documented, and of course comes from MIT. It is also the fastest FFT I've ever used.

I chose it because it is universally available, fully documented, well-debugged, and guaranteed to be around for years to come.

But, it only uses the basic FFT and IFFT functions that are easy to identify with the fftw_ prefixes, and the custom view stuff doesn't use the IFFT (the phase vocoder does).

You are free to replace it with another library and you will need to change the code that calls the FFT functions. It is not too difficult because of the limited range of function calls; fftw_execute is the forward FFT function call. The data buffers are prepared prior to that. 

The dependency on FFTW is limited to only calling the FFT functions and I've had a few users replace it easily with their own FFT versions.

Hope that helps,


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