[sdiy] Speaking of the Elektor Vocoder (and the Korg Vocoder)

Richard Wentk richard at skydancer.com
Wed Feb 20 19:22:37 CET 2008

On 20 Feb 2008, at 17:01, anthony wrote:

> I suppose a filter-bank could be thought of as a crude or coarse  
> FFT. The more and narrower the filterbanks the more it would come  
> to approximate an FFT - maybe in this case FT. Well actually, doing  
> it analog, it's sort of instantaeous.

It sort of isn't, because the envelope followers have a time constant.

> But I wonder if the transfer function of a bunch of filter banks  
> has the same math behind it as the actual  Fast Fourier Transform,  
> which as I understand it, is a recursive algorithm.

No, and no.

Digital filters use a weighted delay matrix with feedback paths  
(sometimes with some non-linear distortion) and work on a continuous  
stream of data.

The FFT is a windowed function which works on blocks of data,  
transforming them in place.

There's no reason why you couldn't code a continuous high-quality  
1024 way digital bandpass filter bank. It might even be more  
musically useful for some applications. But it would have different  
time domain characteristics to a phase vocoder FFT, and would very  
likely sound somewhat different too.


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