[PD] fft beginner question

[Mathieu Bouchard]

On Wed, 21 Nov 2007, Frank Barknecht wrote:

> 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!

I don't think that you can think of the time dimension as a value of what 
comes into the object: I'd say that it is the index of the amplitude. Only 
amplitude is transmitted: time is part of the structure of the actual 
transmission, not the content.

Anyway, that idea would make the complex fft take three inputs: real, 
imaginary, and time.

What [rfft~] does is assume a zero imaginary part. There's a special 
version of the FFT algorithm that is only a slight optimisation because it 
can assume that the imaginary input is zero. [rifft~] can assume that the 
imaginary output is zero or maybe just not wanted, so it can make 
different optimisations.

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