VCO stuff

[Magnus Danielson]

> > From: 	Bert Schiettecatte[SMTP:Bert.Schiettecatte at hookon.be]
> > 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! :-)

Yes, that's cool and usefull... but always have either a "strait" CV jack 
(which
is NOT scaled... it's a hell of a job scaleing rigth!) or a click-in 1:1 scale
on the POT. I think a separate jack is better. For instance does the MS-20
partly suffer from lacking an "strait" CV input jack for the VCOs and the VCFs.

> 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. :-)

Also, makeing an proper mix of the LP, BP and HP output of an state-variable
filter will give you an AP filter! Maybe a mix of the three outputs and the
input signal.... maybe also have an AP signal summed correctly drop.

> 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?

You could do an VCA/Ringmodulator in one step given that the cursuit will
support it. Then you can have separate inputs for ring-modulation and VCA 
control and then simply add them. Maybe not *so* usefull but maybe someone will
eventually find a patch for it. Maybe a input for which you can blend from
ringmodulation and pure VCA function of a input signal.

I think that haveing multiple outputs can be usefull, especially on VCOs and
envelope generators.

VCAs should have multiple inputs.

Magnus