[PD] fft beginner question

[Mathieu Bouchard]

On Thu, 22 Nov 2007, Chuckk Hubbard wrote:
>> If I run two rfft's from the same signal, and multiply the imaginary
>> outputs, do I get negative squares?
>> I'll see...

Pd does not support Complex numbers directly, and so any Complex signal is 
represented as two Real signals, in which you have to do all the Real 
operations yourself. It's worth making abstractions that do it for you, 
but you still have to connect twice the cables.

If Pd supported Complex numbers directly, there would be only one inlet 
and one outlet in plain [fft~], and you'd be able to use [*~] or perhaps a 
new [complex*~] to handle this multiplication with one inlet and one 
outlet.

A single-object way to make the complex product is:

   [expr $v1*$v3-$v2*$v4;$v1*$v4+$v2*$v3]

And then you can see that only plugging the same value in both imaginary 
inputs ($v2 and $v4) gives a real output of minus the square, and an 
imaginary output of 0.

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada