Vocoder Idea

[Magnus Danielson]

>>>>> "CH" == Christian Hofmann <chris at scp.de> writes:

 CH> On Fri, 5 Jun 1998 09:50:34 +0200 (MET DST)
 CH> Martin Czech <martin.czech at intermetall.de> wrote:

 >> 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.
 >> Say fmin=40Hz ->Tcycle = 25ms, if we need 3 cycles to run in this makes
 >> 75 ms just for the lowest channel. Adding time for the other channels
 >> will lead to s&h update intervals of > 0.2s, this seems
 >> to me as a very slow response of the overall system.

 CH> That is, if you're trying to emulate normal vocoder operation.

 CH> But the idea of inserting S&Hs into the channels' VCA control signals
 CH> may produce some interesting FX (well, I guess it won't improve speech
 CH> quality :-)   Has anyone tried something like that?

Yes. It's have allready been made. In the ETI/Powertran Vocoder you
have S/H on every bands CV. You can "lock" them with a footswitch.

I happend to have such a vocoder and there is some wiring and minor
details to attend to until it is operating. This is being under
progress so I should be able to report on it since this is one of the
features that I like to try out since it is not in my other vocoder (a
Korg VC-10).

 CH> BTW, what about completely _synthesizing_ the control signals, e.g. using
 CH> a shepard generator and thoroughly mixing up the channel numbers...? Or
 CH> multiple random voltages in the LFO freq range (as used in the good old
 CH> Elektor Formant).

Hmm... interesting thougth. Maybe I should have CV insert points into
my ETI Vocoder so I can plug in the Formant or whatever there...

I think that part of the trouble is to get an interesting soundcape
change to occur on those CVs.

Cheers,
Magnus