[PD-dev] rfft~ behaviour

[guenter geiger]

On Sun, 29 Feb 2004, Tim Blechmann wrote:
> hi all,
>
> i'm currently working on an external that's using the fftw3 library to
> replace pd's internal fft objects...
> the results are amazing, i reduced the cpu load for the real forward fft
> to 40-50%
>
> but i realized that the imaginary output of the fftw library is
> negative, the imaginary output of pd's fft is positive ... or to be
> exact, the output of fftw and pd's fft are complex conjugated ...
>
> any idea, what could cause this?

Just a guess, but this might be an interpretation issue of what a
rfft is. As it just throws away half of the spectrum, it seems
that they don't agree on which half has to be thrown away.

Are you going to release the objects as externals ?
I think it would be better to have them in the pd sources, and let
configure detect the availabilty of fftw, and compile accordingly.

Guenter