VCO stuff

Dan Higdon hdan at
Tue Aug 6 21:08:08 CEST 1996

> From: 	Bert Schiettecatte[SMTP:Bert.Schiettecatte at]
> what would be cool/extravagant/new controls/buttons/switches to put on a 
> VCO ?
> what on a VCF ? VCA ? LFO ?

I assume you mean on a custom design, and not just for show? :-)

Here are some ideas I've had/stolen for Wally.  Most of them
are still only ideas. :-(

General CV input:  Always use one of those attenuators that will
    let you vary the CV input from -CV..0..CV over the range of the knob.
    That lets you easily apply a negative scaled CV or positive with just
    the spin of a knob.  This is WAY cool, since you don't need any sort
    of inverter modules or special inverted inputs/outputs.  However, it
    does cost one additional opamp per input.  I say, live with it! :-)

VCO: Internal self-frequency modulation.  There is a ElectroNotes design
    that does this, with the self-modulation amount controlled by an internal
    VCA.  Very cool looking, but I haven't heard or built one yet.

VCF: HP/LP blend on a bandpass filter.  I think Christopher List first turned
    me on to this idea.  Basically, set up a pot to vary the output between
    HP and LP.  He (Christopher) claims that this produces some very cool
    phasing and such.  Naturally, you would keep the BP output free. :-)

VC Envelope: Creating a "slope shape" control that allowed +/- feedback
    into the CV inputs for the envelope time.  Another Christopher List
    idea (though I first saw it in Terrence Thomas' book), I would make the
    feedback explicit and give it its own knob.
    (BTW, a VC envelope is any attack/decay/etc generator in which you can
     vary the length of a stage with a CV input.  If you feed the envelope out
     back into one or more of the CV inputs, you can cause nonlinear slopes
     and such.  Ideally, you would have a scale knob that would scale the
     CV between +CV and -CV so that you could have log and exp slopes.)

LFO: Use Ric Miller's (and ElectroNotes') LFO design that lets you
    continuously vary the triangle/square between 10% and 90% width.
    This is a very cool LFO that can approximate saw and reverse saw
    shapes (and all triangles in between), as well as square/pulse waves.
    If you could create a symmetry variable sine wave to go with this, that
    would be very cool/extravagent/new/fresh-and-full-of-life. :-)

VCA: I dunno.  It's a VCA, what can you do with it?  Anyone?

Dan Higdon (hdan at

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