KVR Audio

Bunnyboy · Post by **Bunnyboy** » Thu Oct 14, 2004 9:41 pm

Hello All

I have seen this phrase quite a lot - apparently some filters "self-oscillate" at certain frequencies.

What does this mean? when does this happen? Will Batfink escape with Kato?

WhiteNoise · Post by **WhiteNoise** » Thu Oct 14, 2004 9:58 pm

hehe.. Well a filter will self oscillate at any frequency as long as the resonance is turned up enough.. Basically this means that the resonance is high enough that it makes a pure sine wave at the cutoff frequency. So, you can kinda use the filter as an oscillator in itself.

Borogove · Post by **Borogove** » Thu Oct 14, 2004 10:06 pm

Bunnyboy wrote:I have seen this phrase quite a lot - apparently some filters "self-oscillate" at certain frequencies.

Like WhiteNoise said - if you turn up the resonance on a filter, it squeals; as the resonance gets higher and higher the squeal lasts longer and longer past the point where the input signal to the filter stops. Some people consider this a feature of the filter, some consider it a bug. Synth designers can limit the resonance to keep it from happening, or not -- if not, then "the filter can self-oscillate".

Bunnyboy · Post by **Bunnyboy** » Thu Oct 14, 2004 10:08 pm

WhiteNoise wrote:hehe.. Well a filter will self oscillate at any frequency as long as the resonance is turned up enough.. Basically this means that the resonance is high enough that it makes a pure sine wave at the cutoff frequency. So, you can kinda use the filter as an oscillator in itself.

Aha! Resonance rather than frequency!
Does that mean you can use a filter for amplitude modulation? or am i talking rubbish?

Also this is counted as a good thing. What would be the benefits of a self-oscillating filter?

Borogove · Post by **Borogove** » Thu Oct 14, 2004 10:22 pm

Bunnyboy wrote:What would be the benefits of a self-oscillating filter?

Inducing diarrhea in small children.

Bunnyboy · Post by **Bunnyboy** » Thu Oct 14, 2004 10:24 pm

Borogove wrote:
Bunnyboy wrote:What would be the benefits of a self-oscillating filter?
Inducing diarrhea in small children.

that can only be good

René · Post by **René** » Thu Oct 14, 2004 11:04 pm

Some people consider this a feature of the filter, some consider it a bug. Synth designers can limit the resonance to keep it from happening, or not -- if not, then "the filter can self-oscillate".

Oh that movable line dividing 'bugs' and 'features'

-René

duncanparsons · Post by **duncanparsons** » Thu Oct 14, 2004 11:32 pm

René wrote:Oh that movable line dividing 'bugs' and 'features'

-René

M$ have built a corporate strategy based on it..

I hope that wasn't libellous.. ahh, no, only falsehoods can be libel..

!

DSP

useruseruser · Post by **useruseruser** » Thu Oct 14, 2004 11:38 pm

Borogove wrote: Some people consider this a feature of the filter, some consider it a bug. Synth designers can limit the resonance to keep it from happening, or not -- if not, then "the filter can self-oscillate".

I recommend you to listen to the first "Extras/Durchgeknallt - Frostwave The Resonator" example in the Filter Audition Poll (see my signature).
There You can actually hear the so-called "BUG" of an amazing ! real analog filter unit ! in action. It is merely virtuous self oscillation, which is used to demonstrate this (definitively) FEATURE of philtering...

Bug...

Rubbish. Never heared anyone seriously naming this a bug...

What a bullshit.
.

Borogove · Post by **Borogove** » Fri Oct 15, 2004 12:05 am

jackle&hyde wrote:this (definitively) FEATURE of philtering...

Bug...
Rubbish. Never heared anyone seriously naming this a bug...
What a bullshit.

Don't beat around the bush -- you can tell us how you feel!

shamann · Post by **shamann** » Fri Oct 15, 2004 12:30 am

Borogove wrote:
jackle&hyde wrote:this (definitively) FEATURE of philtering...

Bug...
Rubbish. Never heared anyone seriously naming this a bug...
What a bullshit.
Don't beat around the bush -- you can tell us how you feel!

Actually, I think he was holding back!

Steven West · Post by **Steven West** » Fri Oct 15, 2004 3:42 am

Ah, the 'pings' of my old CS10. It's filter (to me) self oscillating was the best.

Now when you get into sub-oscillating LFO speed, that's the real biscuit!

Listen to my Robin On A Rainy Day at the link below, and you'll hear what I'm mean.

Self-Oscillating Filters - What? How? When?