Thanks to everybody for the answers, For the moment I think that I will try to slightly expand http://ofb.net/~wnoise/haskell/FFTW/ that was pointed out to me by Patrik Sellin with respect to Dan J. Bernstein's library http://cr.yp.to/djbfft.html I was not aware of it, but I would like to have also non power of 2 grids... so FFTW. Fawzi