Vocoder Idea

[Martin Czech]

> 
>    > So the VC-bandpass will perform a frequency sweep
>    > of the "voice" signal, which is sampled by each VCA at the time
>    > corresponding to the freq of that VCA matching the freq of the bandpass.
>    > 
> 
>    I have the impression that this channel saving trick won't work.
>    The analysis filter needs some time to measure the incomming
>    spectrum correctly, and this time is inverse proportional to the
>    filter frequency (Fourier Theory). This would mean that the filter
>    has to stay very long at the lowest frequencys in order to run in,
>    so the overall analysis response will be very slow.
> 
> You could use separate fixed filters for the lowest frequency bands,
> the slow guys, and sweep the rest.

That's true. So for the fixed filters one would have say a fmax of say
about 100 Hz, that is 6 fixed filters or so. But then I would add one
fixed filter and a modulation circuitry, it is much easier to vary the
frequency of a triangle/sine wave osc. then tyhe frequency of a steep
bandpass filter with 8 poles.  Of course this would require a relativly
complex control section.  Shift the incomming spectrum, wait, measure,
s&h, shift again...  Sounds nice. It would be possible to change the
filter characteristic as well as the number of "channels".

The s&h will give a kind of stepped synthesis information, but there where
proposals for better envelope followers that had the same "problem".
Any envelope follower will show some kind of "ringing" if the incomming
frequency is near to the envelope follower filter.

m.c.