[sdiy] filtering cv

[Scott Stites]

Yep, David's 2 cents bought a lot of truth!

Tonight I finally remembered to try out the DC input of the filter, and it
certainly did slew the CV in a most pleasing manner.

Putting the filter close to the edge of oscillation, or into oscillation,
did result in some pretty interesting and cool FM, dynamic depth sort of
stuff.

Anyway, before powering down, I recorded a little trifle using the Thomas
Henry filter to process a repeating gate signal that is modulating my
discrete 2040 filter, which is just at resonance.   It came after a session
of playing with an adaptation of the Buchla 194 BPF that Jeff Pontius put on
half a Futurlec 777 protoboard and sent to me (a very cool module indeed).

There's a bit of the 194 BPF, my quad LFO, quad VCA and Mixer Model 3 in
there too, not to mention the ever-present Rene Schmitz VCO3's.  It's, um,
interesting (at least to me).  I am perpetually aghast at how much variation
one can get out of just a few modules.  If design just stopped now on
everything, I could coast the rest of my life on what's already been done.
Gad, it's late, I'm starting to wax philosophical.  I better sign off.

The sample is here, on my much neglected 'Birth of a Synth' page, under '15
July', top of the page:

http://mypeoplepc.com/members/scottnoanh/slsdiy/id18.html

Cheers,
Scott



----- Original Message -----
From: "Cornutt, David K" <david.k.cornutt at boeing.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, July 15, 2004 11:49 AM
Subject: RE: [sdiy] filtering cv


>
> From: gregory zifcak [mailto:zifcak at hotmail.com]
>
> >thanks for all the replies. so i guess the self-oscillation would add a
sine
> >wave pitch modulation related in speed to the lag time set by the cutoff.
i
> >still can't visualize the effect as resonance is swept from zero up,
going
> >from simple lag to the addition of a sine wave. i'll have to find a way
to
> >try it out.
>
> My two cents: Remember that the step in the sequencer output
> is basically an impulse, which in the frequency domain is a
> short blast of high frequencies.  So, at a low resonance,
> the characteristic would be determined by the cutoff frequency.
> As you turn up the resonance setting, the impulse will start
> to excite the resonance.  At first you will probably hear
> something that sounds (if the cutoff is turned up high
> enough) like a glitch or spit coming from the VCO.  As
> the resonance goes up higher, the impulse will drive the
> filter to a lightly damped oscillation, so you will get
> the sine wave diminishing over a period of several seconds.
> The result will probably sound like varying the modulation
> index in an FM setup.
>