[PD] OT: faster than Fourier transform

Mathieu Bouchard matju at artengine.ca
Thu Feb 2 22:07:55 CET 2012

Le 2012-02-02 à 02:36:00, Ed Kelly a écrit :

> Still the problem with any window-based FFT is that we have to get 
> enough points (e.g. 512, 1024) before we can do the analysis, so there 
> is always a delay (44100/1024 = ~43ms) between live input and output 
> (latency).

Heisenberg's Uncertainty Principle (in its acoustic version) is a hard 
theoretical limit, meaning it can't possibly be violated. All you can do 
is separate the analysis of frequencies so that you get frequent results 
for treble vs less frequent results for bass. This comes at the expense of 
having to customise, complicate and/or slow down FFT to make it do what 
you want.

> Much more interesting is the sliding phase vocoder (Russell Bradford, 
> Richard Dobson, and John ffitch, 2005) where the FFT is adjusted in each 
> sample rather than each frame, and the latency is significantly reduced.

What's the speed of the sliding DFT ?

Note that they call it «DFT», and not «FFT», and that's presumably because 
it doesn't have to do much with FFT... whereas DFT is a more generic term 
for whatever computes harmonics on blocks of discrete signals.

The access to the sliding DFT article is reserved to IEEE members...

| Mathieu BOUCHARD ----- téléphone : +1.514.383.3801 ----- Montréal, QC

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