Rainmaker External Feedback loop

Hi there

I thought I’d try an external feedback loop with Rainmaker to see what additional possibilities it offered for Karplus Strong synthesis beyond the 4 filter types in the internal feedback path. I thought that using a complex filter like Morgasmatron would offer some additional sculpting capabilities. I got some unexpected results when I did this and wanted to see if anyone had suggestions.

The Patch

  • Start with P38: KarplusStr
  • Tap output with stackable cable, one side to audio output, the other to Morgasmatron input A
  • Morgasmatron mix out to external mixer channel 2 in
  • Filtered, enveloped white noise to external mixer channel 1 in
  • Mixer out to Rainmaker in
  • Rainmaker comb feedback all the way down
  • Mixer channel 1 (sculpted noise) close to unity gain
  • Slowly bring up mixer channel 2 (filtered feedback circuit) to increase the feedback amount

I was expecting raising mixer channel 2 to have a similar effect to increasing Rainmaker’s comb feedback dial - that it would lengthen the decay of the sound.

What actually happened is that it didn’t do much of anything. I tried removing Morgasmatron from the feedback path, routing Rainmaker’s output directly back to it’s input (through an attenuator). Same thing. Little to no result on the sound with low amounts of feedback. As feedback is increased, it adds more of a rumble to the sound but didn’t really increase decay time.

Any thoughts on this?

Interesting. I’ll have to give this a shot and see what I come up with.

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OK, I messed around with this and did get some cool results. I shot a little video but unfortunately I wont be able to post it until Monday.

Are you using the Morgasmatron in the feedback loop in Bandpass mode?

Awesome - much looking forward to your video when you’re able to post it.

I’m pretty sure I tried BP. I tried quite a few different things, though I think mostly LPF.

OK here it is. It’s a little long and meandering because I was just filming as I experimented with things, but it’s worth skipping through to see where things end up.

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I thought the whole thing was pretty interesting! It never quite did what I would have expected it to, which is to behave very similarly to the comb’s internal feedback circuit. But you got some really interesting sounds out of it nonetheless.

Definitely worth some further experimentation for me. Seems like using Morgasmatron in bandpass mode was pretty key. You never got the weird rumbling that I did.

Thanks for making this video! Good stuff. :slight_smile:

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Glad you enjoyed it! I had fun making it, too.

I did get some more rumbly tones with larger comb times, keeping the comb shorter provides more tonal feedback.

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Keep in mind that there is a significant delay being added in by your external feedback loop. The Rainmaker itself has a delay/latency of about 2msec caused by the A/D and D/A converters. Then the Morgasmatron will add some delay (frequency dependent to boot!). For pitched Karplus-Strong you need very short delays. With the delays added by your external feedback path you will only get rather low frequency K-S, hence the rumbling.


Thanks. I’ve been trying unsuccessfully to explain to myself why this didn’t quite work as I’d expect. Now it all makes sense!

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