[PD] Cross correlation using FFT

[Jamie Bullock]

On Thu, 6 Apr 2006 18:54:55 +0000
Jamie Bullock <jamie at postlude.co.uk> wrote:

<snip>
> 
> Please find attached, my attempt at making this into a PD patch. The array 'proper' contains a snapshot of the output of from my PD extern, which performs time domain cross-correlation, and what I believe the output should look like.
> 
> The output to the 'output' array is clearly wrong, but I'm not sure why.
> 
> The complex product subpatch is based on one of Miller's examples, I can't remember which. Not sure if the -1 multiply for complex conj (added by me) is implemented properly...
> 

I'm still trying to work this out and getting into more knots. I thought I'd strip it back to the basic maths.

Am I right in saying that the basic operation FFT(x) * conj(FFT(y)) works like this:

(x + ix')(y - iy') = (xy + x'y') + 0i 

?

Jamie