Roland Feedback Oscillators?

[justin3am]

I've been trying to emulate the Roland Feedback Oscillators that are in my V-Synth (and I guess also the JP-8000 and SH-201) with Zebra but I've had little success so far. I figured that it's just a comb filter tuned to a saw tooth oscillator with control for pitch, harmonics (comb detune?) and feedback. Unfortunately, using this seemingly simple formula doesn't get the sound as close as I thought it would.

I have a saw wave in Zebra that sounds very similar to the Feedback oscillator with the Harmonics and Feedback turned all the way down but once I bring the comb in I can't get as close as I'd like to the Feedback Osc sound...

Give me some minutes, I'll post some patches and MP3s to illustrate.

Ultimately, I want to reproduce a patch I made on my V-Synth with Zebra so I can make it part of my patch bank.

Here we go...

V-Synth: http://www.3amnoise.net/fboscVsynth.mp3
The first time I hit the keys it's just the saw wave, the second I fade in the feedback, the third I fade in the feedback then the harmonics then I mess with the harmonics and pitch

Zebra: http://www.3amnoise.net/fboscZeb.mp3
Same thing as above but I'm adusting the input/dry instead of feedback and tune instead of hamonics

Here is the Zebra patch...
http://www.3amnoise.net/FeedbackOscillator.h2p

Thanks guys.

[jupiter8]

Have you tried and sampled the wave with different amounts of feedback and build a wavetable of it ? I have no idea if that is a better approach but it is an idea.

[Urs]

Yeah... these fb oscs were the one thing that I liked most on the JP8000 when I tested it... 10 years ago...

I have no clue how they work though...

Hmmm...

Cheers,

Urs

[Howard]

Maybe hard-sync the oscillator to a phase-shifted version of itself, from 0 to 180°? No idea what that would do (if anything) - just a thought...

Ah, no (just tried it on my V-Synth) - definitely a feedback delay thing. So what would the above do - can anyone try it on something e.g. Nord Modular?

[justin3am]

Thanks for the thoughts guys... I think I'm gonna make do with the results I've gotten. They aren't perfect, but they don't need to be, there is so much modulation going on. I often prototype sounds on the V-Synth then translate them to other synths to see if I get unexpected pleasant qualities, which seems to be the case here.

Anyway, I may still try loading samples of the Feedback Osc into Zebra but I'm not worried about getting the sound down exactly, just close enough for rock and roll.

[Mighty Pea]

Thanks for sharing the preset! Sounds like an interesting technique