Vocoder Idea

[Brian Towles]

I've just started looking at vocoder schematics and flowcharts and had
an idea for a slightly different arrangment:  instead of using a
separate bandbass filter for each channel of the "voice" signal, use a
single VC-bandpass that goes into the normal rectification and LP.  This
output feeds a separate VCA for each filtered channel of the input
signal.  The trick would be to have the values of each VCA controlled by
a sample-and-hold circuit.  The SH for a given channel would be
triggered when the VC-bandpass's freq corresponds to the freq of the
given input channel.  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.

One problem might the rate at which you could perform this sweep -- will
it be limited by the cutoff of the LP envelope filter?  Maybe the LP
should be voltage-controlled, too.  Then the sweep could move at a
constant number of octaves/second.  However, what might be really cool
is a slow sweep or a triggered single-pass sweep.  Speech might not be
understandable, but you could effectively store a filter based on
"voice" patterns over time.  Or maybe even random triggering?

Maybe I should stop studying computer engineering, or start designing
analog computers :)
Brian