FFTW is a problem, since it is GPL (not LGPL as codec2). Non-free licenses
are available for a fee from MIT. I'm not sure they'd license it for
distribution as LGPL, even for a fee, because that would pretty much ruin
their income venue as people could then grab FFTW from codec2 as LGPL.
--------------8<--------------8<-------------
*Ronan Paixão*
2012/1/20 Brian Smith <[email protected]>
> Rick van Rein wrote:
> > Hello,
> >
> > This would seem to be of interest to Codec2: a Faster-than-Fast
> > Fourier Transform designed especially for sparsely filled spectra:
> >
> > News article:
> > http://web.mit.edu/newsoffice/2012/faster-fourier-transforms-0118.html
> >
> > Paper (free download, as public-funded research ought to be):
> > http://arxiv.org/abs/1201.2501v1
> >
> > The algorithm achieves O(k.log(n)) if the input signal has at
> > most k non-zero Fourier coefficients. In terms of Codec2, we
> > could expect k=10 over 320 samples, so O(2663) becomes O(133).
> >
> > Roughly -- and background noise would worsen these figures.
> > The Codec2 encoder spends about 1/3 of its time in FFT.
> >
> >
> > Cheers,
> > -Rick
> >
> >
> An alternative would be to use FFTW instead of Kiss-FFT, which runs
> roughly twice as fast, presumably by pre-computing the required
> sine/cosine values used in the transform.
>
>
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