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

[David Moylan]

Eric Brombaugh wrote:
> 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. 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.
>>
>> Math guys?
> 
> Not really a math guy, but I'll take a stab at it. :)
> 
> In general, no. Specifically, it depends on what kind of filter bank 
> you're talking about.
> 
> An FFT is a specific algorithm for implementing the Discrete Fourier 
> Transform (DFT) which optimizes the number of multiply/adds required. In 
> order to support the optimization, the FFT imposes certain limits on the 
> amount of data you transform (although there are tricky ways to expand 
> the possible data sizes). The FFT is an iterative (but not recursive) 
> algorithm - the number of iterations depends on the data size.
> 
> The underlying math of the DFT is very different from the processing 
> that's taking place in a typical analog filter. A closer analogy to DFT 
> processing would be more like what happens in a radio receiver.
> 
Right, I forgot that the Fourier transform is specific to periodic 
waveforms and breaking them down into component harmonic partials.  A 
vocoder acts on the entire spectrum (with limited resolution).

Dave