Feedback Osc trough filter


I try to replicate this Elektron Analog 4 technics for creating a feedbacking osc trough the filter.

Do you have any tips for doing this technique? I join you below the technique described in the manual of the analog 4

“FDB This setting is only available to OSCILLATOR 1. Instead of using the oscillator waveform as the
audio source, the audio coming from the ladder filter output will be used. Just as with the oscillator,
the LEV parameter sets the level of this signal path. Turning it up high can introduce a self-oscillating
feedback useful for drums or uncontrolled screams. The filter cutoff and resonance settings also
affect the feedback behavior. On more moderate levels, it will give a more overloaded sound character
to whatever enters the filter from OSC2, similar to the external feedback patch known from certain
1970s synths.”


Hi @laminak,

I haven’t tried to replicate a self-oscillating filter effect with any of Sonic Pi’s FX yet, though I suspect it might? not be easy. Happy to know if anyone would be able to suggest otherwise though!

Having said that, Sonic Pi’s synths and FX are designed and built using the language of the sound engine that runs behind it (Supercollider) and there appears to be a special filter type available for Supercollider that allows self-oscillation - ‘DFM1’. It would most likely be fairly simple for us to add this filter to Sonic Pi.

Hi @ethancrawford thanks for reply

Good idea for the DMF1 filter, but I have no idea how to achieve this …

I don’t think it’s possible to recreate that feedback behaviour, because the filter effects only allow resonances <1, so no self-Oscillation happens.

You can wrap a :pnoise synth in a :rlpf effect with the resonance at 0.99999 or higher to create a similar sound.
Not exactly the same, but you don’t have to worry about volume envelopes.

Hey @laminak

Sorry for the confusion. I meant that at least for the core Sonic Pi developers it looks like it would be a fairly straight forward thing to add to Sonic Pi.
I may have a go at adding it in soon :slightly_smiling_face:

I’ve had a go at adding DFM1 into Sonic Pi. Almost got there - there’s one challenge with it: working out how to ‘kill’ the effect after the appropriate amount of time. (On my build it currently stops too early). Other than that, it seems to work great.

@ethancrawford That’s very good news. A big thank-you !