Building a feedback loop - looking for ideas, techniques

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challism
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Post 22 Nov 2021

I'm working on a multi-effect Comb2 that will rearrange the order of the effect units from buttons on the Combi faceplate (all possible orders in serial will be represented, effects can be replaced/drag n dropped and it won't affect the assignments). I'm wanting to add just a little something extra, so I'm thinking and adjustable feedback loop, where each of the effects can adjust the amount of feedback they contribute to the loop (loop and contributions can be optionally muted).

Anyway... I'm pretty much done with the device except for photoshopping the graphics and coming up with some more interesting ideas/methods for the feedback loop reminiscent of LoveOne Photon or Ekss OUROBOROS. Who better to ask than the fine users of the RT community?

Thanks in advance, and I will be sharing the Combi patch here on RT, in the Combi2 subforum, when I'm done.
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Loque
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Post 22 Nov 2021

Everything can be used as long as it has some delay on it.
Reverb, delay, reverse, glitchy stiff, filtering, soung shaping, arpegiats, pitch, frequency, stutter, fm, am, ... All in any combination
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deeplink
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Post 22 Nov 2021

I guess it can be anything, the more creative stuff as loque mentioned above is like reverse, pitch, gaters etc.
RS's Polar with its Loop/RevLoop mode, feedback and pitchshifting leads to some pretty wild stuff.
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MarkTarlton
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Post 22 Nov 2021

Something fun to play with is layering the tail of a reverb pitched up an octave sent through a feedback loop on top of the dry signal for the shimmery type of effect that you hear in Photon. I tend to favor a longer diffused type of verb for this.

Another thing to play with that I am a fan of is adding a filter that sweeps around in the feedback loop, so you can get some cool sounding regenerations that swoosh, or maybe rumble depending on if you are higher or lower up in the frequency register. A limiter would probably be required so you don't fry anyone's speakers or hearing :)

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challism
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Post 22 Nov 2021

Thanks for the input (I really wanted to say feedback)

I think the most important thing for a feedback loop to have is a kill switch, as they tend to get out of control very easily. I've also got a limiter running on the master audio outputs.

The thing I like best about the combi I'm building is all the FX devices can be easily swapped out and combi assignments won't be lost. I'm assigning the combi controllers to utilities. I think I've just about got all the universal knobs and switches assigned that I want (17 switches and 16 knobs used so far). I'm looking at this combi patch as a template/starting point. The rest of the available knobs and switches are left available for users to add and customize the effects devices inside the combis. I really hate that we are limited to 32 of each.

The thing I like least... it's a hungry bugger. Scarfing down those DSP crackers.
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selig
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Post 22 Nov 2021

challism wrote:
22 Nov 2021
Thanks for the input (I really wanted to say feedback)

I think the most important thing for a feedback loop to have is a kill switch, as they tend to get out of control very easily. I've also got a limiter running on the master audio outputs.

The thing I like best about the combi I'm building is all the FX devices can be easily swapped out and combi assignments won't be lost. I'm assigning the combi controllers to utilities. I think I've just about got all the universal knobs and switches assigned that I want (17 switches and 16 knobs used so far). I'm looking at this combi patch as a template/starting point. The rest of the available knobs and switches are left available for users to add and customize the effects devices inside the combis. I really hate that we are limited to 32 of each.

The thing I like least... it's a hungry bugger. Scarfing down those DSP crackers.
Well, you can't have feedback without an input, so…

One thing to look out for is DC build up with loops, you will almost always need a HP filter in the FB path to control this. My Shimmer Verb Combinator based on Love One's Neutron taught me that (using Pulveriser's HP filter set to 24.8 Hz), and I see Gustav allows you to add a HP filter in Photon's feedback path as well. In my experience you only really need it for high feedback settings, but without HP filtering you'll get runaway DC easily with those settings.

And remember the limiter doesn't actually stop runaway feedback in all cases (especially if it's not in the FB path), it just tries it's best to keep it at a respectable level. You still need to hit that kill switch in those cases!

There may be ways to optimize the DSP hit by trying alternate devices for any task where there are options.
Selig Audio, LLC

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challism
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Post 22 Nov 2021

selig wrote:
22 Nov 2021
challism wrote:
22 Nov 2021
I think the most important thing for a feedback loop to have is a kill switch, as they tend to get out of control very easily. I've also got a limiter running on the master audio outputs.
Well, you can't have feedback without an input, so…
Touche! OK, the SECOND most important thing is having a kill switch. Can't get anything past Giles, can I?

Thanks for the tips. I've also found that a HP filter is crucial. Good point about the limiter.

The biggest problem with the DSP, in this case, are the number of devices in the combi. Even if the utilities are using a small amount - even 0.5-1% CPU usage - it still doesn't take very long for the combi to be hitting some big CPU% numbers. Luckily, my computer is old AF and on its last leg!
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