[PD] fft beginner question

Frank Barknecht fbar at footils.org
Wed Nov 21 19:21:49 CET 2007

hard off hat gesagt: // hard off wrote:

> >>cos^2+sin^2=1
> ah!
> so, actually the FFT doesn't HAVE to use imaginary numbers....but they
> are just used because "the complex-number system is
> two-dimensional and that signals to be analysed are presumed to be
> two-dimensional. They are decomposable into a sum of circular
> trajectories"
> every day a bit more of this falls into place.

An interesting thing to note is that the rfft outputs two signals,
where seemingly only one signal comes in. How can that be?  Actually
what comes into the rfft object are two values as well: One is the
usual signal amplitude visible as a patch cord, and the other is:

Time is not visible in Pd, it's just there and normally always walks
on. But inside of a FFT-subpatch, time is frozen for the duration of a
block (or rather: the "current time" is assumed to be infinite or
eternal) to allow calculating a different representation: the
frequency domain representation. If you think about this freezing of
time for too long this is actually quite mind-blowing as well.

 Frank Barknecht                                     _ ______footils.org__

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