[amo] Operator: SVF Filters don't actually self-oscillate

[prebentious]

Load a default Operator
Change filter type to any SVF filter and set resonance at maximum
(it's also handy to right click the freq knob and select 'Play By Key' (cool feature!))
Lower the volume of osc 1 to 0.
playing notes on my keyboard produces no sound.
Shouldn't the filter be self oscillating? That's how my analog synth works.

If I turn osc 1 back up and give it a super short envelope, the filter will continue to oscillate after osc 1 dies out, which is cool, but that's not true self oscillation.

[scientist]

Shouldn't the filter be self oscillating? That's how my analog synth works.

afaik no filters in live are programmed to imitate self oscillation...not a bug.

[prebentious]

From page 403 of the manual:

"The SVF (state-variable lter) modes are 12 dB types but with a different architecture. They will self-oscillate as their resonance is increased. "

[scientist]

From page 403 of the manual:

"The SVF (state-variable lter) modes are 12 dB types but with a different architecture. They will self-oscillate as their resonance is increased. "

cool! good looking out. i see what you're saying...its not like using the filter as an oscillator, and i'm not sure if that's what they intended. if i understand correctly, a filter is still 'self oscillating' if it produces a pitch, regardless of whether or not it needs input to make it do it.

yup, from ye aulde wikipedia:
Self oscillation occurs when the resonance or Q factor of the filter is set so high as to cause the filter circuitry to generate a tone on its own after it has been excited by an impulse.

so it needs some sort of exciter, however small.

[prebentious]

I guess my Roland sh-101 is noisy enough that the filter doesn't need the oscillators in order to self oscillate

[Amaury]

Hi,

Indeed, the SVF filter do self-oscillate. They need some impulse, to start self-oscillating. You can set only one of the 4 operators, to noise, with a very short envelope, and as long as you'll hold the key, the filter will oscillate, given you have a resonance set to 10.00 or something very close to that.

By the way, if you right click on the Freq knob of the filter, you'll find a "play by key" command. That sets the filter to follow the frequency of the played MIDI note.

Regards,
Amaury

[timothyallan]

Hi,

Indeed, the SVF filter do self-oscillate. They need some impulse, to start self-oscillating. You can set only one of the 4 operators, to noise, with a very short envelope, and as long as you'll hold the key, the filter will oscillate, given you have a resonance set to 10.00 or something very close to that.

By the way, if you right click on the Freq knob of the filter, you'll find a "play by key" command. That sets the filter to follow the frequency of the played MIDI note.

Regards,
Amaury

Isn't that the handiest thing!