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

[ASSI]

On Freitag 22 Februar 2008, anthony wrote:
> That is exactly what I was saying. If you had 100 or even 1000 fixed
> badnpass filters with high enough Q's and had bar graph meters or
> what-have-you on each one, the result would be a spectral analysis
> much like what the Fast Fourier Transform algorithm would yield.

No, not even close.  A BPF with high Q is otherwise known as a resonator 
and among other things it takes time to respond, rings and decays 
quite, but not entirely unlike an FFT.  Then you'd still need an 
envelope follower or something else that measures the total energy in 
the resonator to get at the spectrum.

> The analog advantage is that each
> band analysis is happening at exactly the same time: great for
> rapidly changing spectral information.

This is simply not true - especially not the part about rapidly changing 
spectral content (and analog vs. digital doesn't have much to do with 
it really).  Each BPF has it's own associated timeconstants and delays, 
as well as the envelope followers associated with it.  The channel 
outputs you get from such an analysator at any instant in time are thus 
caused by signal portions which happened at quite different periods of 
time in the past.  The finer you require the frequency resolution to 
be, the more time needs to go by before you get a correct result.  This 
is no different in the analog domain than in the digital domain.


Achim.
-- 
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