[sdiy] filtering cv

[Cornutt, David K]

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.