Saturday, November 01, 2008
Wasp-like VCF sync demo
YouTube via synthmonger
"Here's a small clip featuring one of my latest VCF modules. This is a wasp-like filter using my voltage controlled oscillator variable resistors (vcovrs) to control the frequency and resonance of the state variable filter.
In the video I have a single oscillator running through the filter while another oscillator is syncing the vcovr which is controlling the filter frequency. The resonance is set at max and is self-oscillating, which is very unusual since state variable filters are not supposed to self-oscillate. I am just adjusting the frequency knobs and showing the different audio outputs. Not much to it! :)"
2 comments:
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Why do you think that state variable filter cannot self oscillate? In fact, most quadrature voltage controlled oscillators are nothing more than a state variable filter with high enough feedback to oscillate. There is nothing preventing a state variable from oscillating except the range of the controls. The serge filters are some of the best I've used because they dont go into oscillation when resonance is turned high, but rather are patch programmable to oscillate. In other words, you can choose if it will oscillate or prevent it as desired. The serge VCFQ is one type of state variable filter among the many different types. The advantage of the serge is of course that you can have very high resonance without oscillation (much higher than a moog ladder filter for example, or have oscillation if you want.
ReplyDeleteHonestly, I don't have much experience with filters as I tend to stick with signal, logic and cv generators. I've only read that SVF were unable to self-oscillate on a couple DIY sites and the EM SDIY forum. I also read that the original wasp VCF was unable to self-oscillate.
ReplyDeleteI should also mention that my first design used every part from the wasp vcf schematic with only the ca3080's replaced with my vcovr's and it was self-oscillating, but it was a little unstable. Since then I've removed a couple components, switched to a 12V power supply and changed the resistor and cap values to get a little more frequency range as well as stability over the resonance.