multiple-type Digisound VCDO thing?

[WeAreAs1 at aol.com]

Josh Brandt wrote:

<< So, I was showing the Digisound VCDO schematic to a friend of mine, and we
were talking things to do with it...

Our ideas-- take the output from IC3b (where it goes into IC4) and duplicate
(or triplicate or quadruplicate) all of the digital circuitry, sending the
same signal from IC3b and running it into 2-4 IC4's, each of which is
connected its own IC9 (the ROM), and so on... Include separate sets of front
panel controls for each set of digital circuitry, and you can individually
select different waveforms for each one (or the same waveforms for each one,
for that matter), and you've got multiple digital sources, all tracking the
same CV. Burn a few more EPROMs, with the same (or different!) waves, and
you've got a nice big flexible module _without_ having to dig up several
CEM3340's. (It seems that making them paired-- one 3340 driving two sets of
digital circuitry-- would be the most expedient.) 

Does this seem a reasonable idea? Am I missing some basic concept here? >>

Of course it's a workable idea, and yes, you'd save a bit of money on the
clocking VCO, but all of your waves would always be exactly locked in phase
with each other.  You wouldn't be able to detune your oscillators or tune
them to different intervals.  As anyone who has played with a Korg
DW8000/EX8000 (or a Wave PPG) already knows, detuned digital wavetable
oscillators sound *great*.  I'd rather spend the extra $15 - $20 and have
more tuning flexibility.

BTW, is there an accepted standard for VCDO wavetable sampling rate, source
wave pitch, and sample-loop byte length?  What are these specs on the
Digisound?  If we could decide on a standard, we could collectively build up
a library of waves which could be easily shared via online binary files.  I
think it would be cool to put a bunch of tweezy pre-MIDI (and post-MIDI)
Casio waves, squirbley FM waves, and annoying Kawai additive waves (not to
mention time slices of choice acoustic events) under voltage control - you
could put 'em on separate EPROMs or fit them all on one big EPROM, with
simple address switching to select the wave you wanted.  

Kevin L.?  Have you thought about this?  What did you plan to use for wave
data, and how will you encode it?  Doesn't the Digisound design use those
Companding (rather than linear) 8-bit DAC's?  If so, it won't be real easy to
encode ROMs, not without a companding ADC (such as an Oberheim Prommer).  The
companding system gets better-than-8-bit fidelity (increasing apparent
resolution at lower wave amplitudes), but linear data would be a lot easier
to convert directly from 8-bit .wav or AIFF files.

Michael B.