[sdiy] modular synth "standards"

[Don Tillman]

   From: jhaible at t-online.de (jh.)
   Date: Sat, 24 Feb 2001 22:34:18 +0100

   I disagree with you here, Don. 

(This means I'm likely to learn something...)

   In all my modulars or semi-modulars, Audio and CV are
   interchangable, and I would never want to miss this. Even in a
   non-modular such as a Prophet 5, the VCOs restricted to being a
   "signal source" would mean no audio rate PWM. (Which is one of the
   P5's best features, IMO.)

Having separate audio and control voltage levels doesn't preclude
audio rate PWM (which is, indeed, a very useful patch).  

This is a very interesting example you bring up, because PWM
modulation could just as easily come from an audio source as well as a
control source.  Or both sources.  As could FM modulation.  But other
than assuming audio input levels and maybe padding down the input for
control voltages, I don't see a problem.

   The Interpolating Scanner is good for mangling CVs as well as Audio
   Waveshaping,

(I believe there are lots of interpolating scanner applications just
waiting to be discovered.)

Yeah, the scanner is a module that can be used on control voltages
just as well as audio signals.  Same with a VCA, ring modulator,
mixer, and a bunch of others.  These modules would be simpler in a
common-control-and-signal-voltage system and would require input level
switches or some other compatibility features in a separate-control-
and-signal-voltage system.

   Why would I want the saw wave go to twice the positive voltage than
   the Triangle ? I find it "natural" to preserve the voltage swing
   when I switch modulation waveforms.

The ARP2600 is the classic example.  The ARP2600 VCOs keep a standard
10V p-p signal, but the sawtooth and square waves have a minimum of 0V
while the sine and triangle waves are centered at 0V.  This is all
for convenience for the typical VCO modulation applications.

It also explains why the most popular ARP2600 modification is adding
AC coupling caps to some of the VCF mixer inputs.

   I think it's all a question of the number of interface points
   needed. 

That's certainly true.  Perhaps I'm a little biased right now because
I'm working on a modular project designed for signal processing.

   It's always a compromise ...

Put a positive spin on it and call it "an optimization".  :-)

   -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com