intersil VCO chips and 'synth-level' circuits...

[Don Tillman]

   Date: Tue, 5 Dec 2000 08:30:25 -0800 (PST)
   From: Nick Zuccaro <nmz77 at yahoo.com>

   i'm planning on integrating some modules with the rest of the gear
   i've got, which is at line level, mic level and guitar/bass level,
   so i'm assuming i'll need some kind of level 'adapter' in order to
   use all of these together. would it be better to use a synth
   level->line level converter to use everything at line level <studio
   standard> to take advantage of passive attenuation, or to convert
   the line level stuff i've got to synth level, which is +/- 2.5v?

The choice of what level to use for audio signals is an important
decision in the design of a modular synth.  Moog and Buchla used
roughly 1.0 Vp-p to match the 0 dBu line level signals of studio
equipment.  ARP, Synthesizers.com and MOTM use 10 Vp-p to match the
control signal voltage range (1.0 V/octave) so that control signals
and audio signals would be interchangable.

(Somebody may want to check on the accuracy of the above numbers.  I
*think* they're right.)

The choice generally boils down to which you want to do more often,
connect to other studio devices or swap audio and control signals.

My personal choice would be to use line level (0 dBu) audio signals.
While matching audio and control signal levels is a potentially
powerful theoretical concept in that it removes many preconceptions of
how a module is going to be used, in practice a module designed for
audio signals is is going to be very different from one designed for
control signals.  

Take a VCO for instance -- a sawtooth wave for audio will be centered
around zero volts while a sawtooth for modulation purposes will start
at zero volts.  A PWM wave for audio should have dc restoration so that
its average value will be zero while a PWM wave for modulation will go
from zero to 5 volts.

  -- Don

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