mixing/modulating

[David Krupicz]

----- Original Message -----
From: <farky at ix.netcom.com>
To: <synth-diy at mailhost.bpa.nl>
Sent: Monday, December 13, 1999 12:30 PM
Subject: mixing/modulating


> Hey folks:
>
> If I had two oscillators, for instance a square and a triangle, and I
> wanted to make a more complex waveform by modulating them together, what
> kind of mixer circuit would I use?

You can do two things, assuming the oscillators are voltage contolled,
modulate frequency, or modulate amplitude (or you can do both..;)    In
either case you will want a VCA to amplify one of the
two oscillators.

For frequency modulation:

    VCO1 > VCA > VCO2
                                freq.

    You can set the level of frequency modulation by adjusting the gain of
the VCO.  Now, where the interesting bit comes in is that you can use any
signal you want to control the VCO, such as an envelope follower or an
envelope generator (ie of the ADSR variety...)      Frequency modulation is
the same thing as vibrato, only the modulation is at audible frequencies.

For Amplitude modulation:
                      cv in
    VCO2 ----.
    VCO1 >  VCA > ---out--->

    The amplitude of VCO 2 is used to modulate the volume of VCO1...  if VCO
2 is slow, then you get tremelo, if it is fast (ie audible) then you get
ring modulation.


Now, wire up about 10 more oscillators, and an equivalent number of VCA's
and you'll have yourself a monster noise creating machine!