Reaktor Blocks SVF self-resonance?

chromastatic · 2022-02-02T19:14:20+00:00

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Hello! The Blocks reference guide says that the SVF in Blocks can self-resonate with the resonance turned up. I haven't been able to make this happen, where SVF functions on its own to create a pitch. I am familiar with this technique in the modular world to make sine waves, kick drums, etc. SVF only works for me with an oscillator plugged. Any thoughts?

From the guide:

"RESONANCE: Controls the amplitude of the signal at the CUTOFF frequency. As resonance

increases, the harmonics around the cutoff frequency appear louder and more pronounced

than in the original signal. At very high settings, the filter goes into self-oscillation, producing a

sine wave on its own. The frequency of this sine wave is set by the CUTOFF control."

Thank you for thoughts and suggestions!

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colB

You are correct. Looking into the structure, the resonance is scaled to be just below 1 at max. I suspect the reason is that this filter is not oversampled, so aliasing is more noticeable.

Try the Paul filter in the Blocks Primes collection, that self oscillates nicely, and is oversampled (switch off the 'bass boost' to get a broader range for the self oscillating sine).

All comments

colB

You are correct. Looking into the structure, the resonance is scaled to be just below 1 at max. I suspect the reason is that this filter is not oversampled, so aliasing is more noticeable.

Try the Paul filter in the Blocks Primes collection, that self oscillates nicely, and is oversampled (switch off the 'bass boost' to get a broader range for the self oscillating sine).

chromastatic

Fantastic, thank you for verifying this, as well as the note on which modules are oversampled!

I'll try it with the Paul Filter. I'm pretty sure I also did this in the past with the SKF.

I was hoping to show this technique to someone who only had the Blocks Base modules, but I understand if there are limitations with those.

chk071

I always thought that self resonant filters need some kind of input, also in the analog world. Try with an oscillator or any kind of audio input. It doesn't have to produce any sound.

Moonbot7000

https://community.native-instruments.com/discussion/comment/4180#Comment_4180

No, a self resonant filter does not need an input, and if it's self-resonating, you wouldn't hear the input anyway.

chk071

Hmm... I don't know much about these things, but, the way I understand it, the self oscillation is caused by a feedback loop? How would that work without input?

colB

https://community.native-instruments.com/discussion/comment/4301#Comment_4301

Internal feedback. You would expect it would need some sort of noise in there to get things started, but I guess the noise from accumulated numerical errors of 32bit arithmetic in the feedback loop is enough?

chromastatic

Thank you everyone for your feedback.

Along these lines, just curious about the nature of self-resonating filters on synth hardware, for example in modular gear. Would a filter self-resonate because of internal noise (from voltage, etc.) or are they designed that way with intentional feedback loops built-in? Maybe it depends on the manufacturer and specific filter design?

colB

https://community.native-instruments.com/discussion/comment/5855#Comment_5855

Feedback loops is literally how most(?) hardware filters work. Some filters don't (FIR filters and RC passives etc., but the ones that sound like hardware and generate proper fart sounds do.

Many hardware modular filters can be used as oscillators, and some even have pretty good pitch tracking. Even some oscillator modules e.g. Doepfer A-110-4 are actually filter circuits with some additional support circuitry for better tracking and stability.

Laureano Lopez

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