Croglin resonance details

[terjewinther]

I am building some Oakley filters, and just completed the Croglin filter today.
Comparing the filter sounds to the sound clips on the web site, it seems to make the same type of sounds, which is good.

Just curious: the resonance is not supposed to go into self-oscillation, right?
Also: even when the resonance pot is at "off " (zero), it still seems to be a good portion of resonance going on. Not that I complain; usually resonance pots on filters often is without interest in the first portion of the pot turning, so I like the idea of having some resonance all the time.

[Synthbuilder]

the resonance is not supposed to go into self-oscillation, right?

The 5U version of the Croglin does not go into self-oscillation.

even when the resonance pot is at "off " (zero), it still seems to be a good portion of resonance going on.

The resonance is very unusual on the 5U Croglin. There always is a little bit of resonance at higher audio frequencies, but this tails off at lower frequencies. Indeed, you'll notice that the resonance isn't very obvious at low frequencies even when resonance is turned up.

The Eurorack Croglin is based on a different filter topology (Sallen-Key 2 pole MS-20 style) so behaves somewhat differently to the 5U Croglin.

[terjewinther]

even when the resonance pot is at "off " (zero), it still seems to be a good portion of resonance going on.

The resonance is very unusual on the 5U Croglin. There always is a little bit of resonance at higher audio frequencies, but this tails off at lower frequencies. Indeed, you'll notice that the resonance isn't very obvious at low frequencies even when resonance is turned up.

Great - thanks!
Yes, I have noticed this: low frequencies behave differently.

I also noticed that when making drones with two very, very slow LFOs at different speed running into the 2 CVs with resonance at full (and the input is a complex static sound with lots of high-frequency partials), the resonant peaks behave quite differently compared to other, more normal filters. It sounds to me like the resonant peaks sort of drift up and down in a non-linear way - and this is really cool! Add some reverb and/or delay to this, and you have a wonderful sound.