digital control of analog component question...

[Byron G. Jacquot]

>My knowledge of synth engineering is pretty damend small, so this question
>is basic.  What does it take to digitally control analogue devices?  Is it
>simply a matter of sending the digital number to a D-A which goes to the
>control-voltage input on the analog devices?

In some cases, that works well...but only if the parameter you want to
control may be voltage controlled.  In many cases, the main parameter of a
module is voltage controller (thus the popularity of Voltage Controlled
Oscillators, Filters and amplifiers).  There are many common designs for
modules with a single voltage controlled aspect, like pitch or amplitude.
But for ones with every parameter being voltage controlled, the complexity
goes up incredibly.

A quick example: with a VCO, it's pretty common for there to be voltage
control over the pitch and pulse width.  But it's uncommon for there to be
voltage control over the waveform.  (Though it is possible- witness the JH
Interpolating Scanner, or some of the single-cycle wavetable designs)  Other
parameters that aren't simply voltage controlled include filter resonance
and envelope segment times.

So to answer the question: for rudimentary control over most synth modules,
you can use a DAC.  But for controlling every single parameter, there are
other techniques which will probably be more rewarding.  If you only desire
to control the voltage-controlled parts of a synth this works quite well.

Of course, there are many happy (some happier than others) solutions, which
give the digital portions control over varying amounts of the analog corcuits.

Byron Jacquot