Distortion in Delay Feedback Loop

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suckerformimi
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Distortion in Delay Feedback Loop

Post by suckerformimi » Wed Feb 12, 2020 11:33 am

I am trying to create a delay effect where the repeats distort more with each repeat. I have been trying guitar pedals but they seem fundamentally unsuited to the task because of the gain they need to distort. So I’m looking for a distortion or waveshaper that will keep distorting as gain is reduced. Is there such a thing?

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Re: Distortion in Delay Feedback Loop

Post by vidret » Wed Feb 12, 2020 12:00 pm

what do you mean when you say guitar pedals are unsuited?

Do you mean distortion pedals or delay pedals? Either way, both are pretty suited to the application (unless the delay pedal doesn't have an fx loop, since that seems to be what you want to do).

you want it to keep distorting as the gain is reduced - do you mean the echoes should keep distorting no matter what the input signal is doing?
Do you want distortion/compression on the echo without the gain/volume of the echo to be present? Patch a compressor in the feedback loop of the delay (as well as any sort of distortion), this should get you there.

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dooj88
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Re: Distortion in Delay Feedback Loop

Post by dooj88 » Thu Feb 13, 2020 9:22 am

i think you need 2 feedback loops here. one as the send from the delay to distortion and back to delay, and a second sub feedback loop with just the distortion (with attenuation).

so patch out of delay send into a mixer (you'll see) then into the distortion, distortion back into delay return input (probably attenuating the signal before the return. but you need a sub-feedback loop to increase the distortion of the repeats. so you'll mult the signal coming out of the distortion, run it through a VCA then back into the mixer that goes into the distortion.

or perhaps i'm waaaaay overthinking this and the second sub loop is the product of excessive amounts of caffeine this morning.
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Re: Distortion in Delay Feedback Loop

Post by cornutt » Thu Feb 13, 2020 3:53 pm

Yeah, that's a little weird, because creating distortion usually means boosting the signal level. But if you boost the level in the delay's feedback loop, the repeats will never fade out -- it'll keep repeating forever, or even run away. It would need something like a compander setup, where it compresses the input going into the distortion box to boost the leve, and then downward-expands the output to restore it to its previous level. Sort of like what a tape noise reduction system does. I'm sure there's a way to patch this up using envelope followers and VCAs, but off the top of my head, I can't think of it at the moment.
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Re: Distortion in Delay Feedback Loop

Post by jorg » Thu Feb 13, 2020 4:55 pm

You need something with crossover distortion; that actually sounds more distorted on small signals than large ones.

suckerformimi
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Re: Distortion in Delay Feedback Loop

Post by suckerformimi » Fri Feb 14, 2020 7:40 am

jorg wrote:
Thu Feb 13, 2020 4:55 pm
You need something with crossover distortion; that actually sounds more distorted on small signals than large ones.
That sounds like what I am looking for. I could not find crossover distortion in eurorack though.

Sorry if I wasn't clear about the issue I am running into. To get distortion the gain has to be high enough that the repeats keep getting louder.

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Re: Distortion in Delay Feedback Loop

Post by starthief » Fri Feb 14, 2020 8:12 am

How about this:

Code: Select all

delay send -> distortion -> VCA -> delay return
delay send -> envelope follower -> invert -> gain/drive on the distortion
              envelope follower -> VCA CV
With some tweaking that might do the trick. It's also possible that you don't need dynamic gain on the distortion because the feedback itself will distort more, but of course, once you've clipped to a squarewave you're not going to get any more clipping. Hmm.
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jorg
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Re: Distortion in Delay Feedback Loop

Post by jorg » Fri Feb 14, 2020 9:02 am

suckerformimi wrote:
Fri Feb 14, 2020 7:40 am
I could not find crossover distortion in eurorack though.
Sorry if I wasn't clear about the issue I am running into. To get distortion the gain has to be high enough that the repeats keep getting louder.
Right; the gain problem is why I suggested crossover distortion; you don't need to add any gain for that.

You could use a rectifier module such as this:
https://www.modulargrid.net/e/cfm-bhwr-rectifier/

...recombine the positive and negative halves of the wave, and you should get some significant crossover distortion.

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Re: Distortion in Delay Feedback Loop

Post by vidret » Fri Feb 14, 2020 10:42 am

jorg wrote:
Fri Feb 14, 2020 9:02 am
suckerformimi wrote:
Fri Feb 14, 2020 7:40 am
I could not find crossover distortion in eurorack though.
Sorry if I wasn't clear about the issue I am running into. To get distortion the gain has to be high enough that the repeats keep getting louder.
Right; the gain problem is why I suggested crossover distortion; you don't need to add any gain for that.

You could use a rectifier module such as this:
https://www.modulargrid.net/e/cfm-bhwr-rectifier/

...recombine the positive and negative halves of the wave, and you should get some significant crossover distortion.

Please expand on this, won’t you just get the original signal back if you recombine them?

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Re: Distortion in Delay Feedback Loop

Post by abelovesfun » Fri Feb 14, 2020 11:11 am

Are you going direct to stomp or using an adapter to match levels? I find there is a night and day difference between the two. Here is a demo of mine:



I would mult the delay repeat out, one clean and one distorted, and use a crossfader module or pair of vcas to control the fade from clean Repeats to distorted Repeats. Assuming I understand what you are looking for.
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Re: Distortion in Delay Feedback Loop

Post by jorg » Fri Feb 14, 2020 11:36 am

vidret wrote:
Fri Feb 14, 2020 10:42 am
Please expand on this, won’t you just get the original signal back if you recombine them?
If the rectifier is built with ideal diodes, yes, you get your original signal back.
But there is no such thing as ideal diodes. So you get crossover distortion.

You could even build this as a little cable with a lump in the middle, with the circuit below. Notice the distortion is worse with a 2Vpp signal than a 5Vpp signal. If you want to make it a little milder, replace the diodes with Schottkys, such as BAT54.
Crossover distortion.PNG
Crossover distortion 5V.PNG
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suckerformimi
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Re: Distortion in Delay Feedback Loop

Post by suckerformimi » Fri Feb 14, 2020 9:22 pm

abelovesfun wrote:
Fri Feb 14, 2020 11:11 am
Are you going direct to stomp or using an adapter to match levels? I find there is a night and day difference between the two. Here is a demo of mine:



I would mult the delay repeat out, one clean and one distorted, and use a crossfader module or pair of vcas to control the fade from clean Repeats to distorted Repeats. Assuming I understand what you are looking for.
Yes, I am using the Doepfer module with the built-in cross-fader. So I have pretty good control of the levels.

suckerformimi
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Re: Distortion in Delay Feedback Loop

Post by suckerformimi » Fri Feb 14, 2020 9:35 pm

jorg wrote:
Fri Feb 14, 2020 11:36 am
vidret wrote:
Fri Feb 14, 2020 10:42 am
Please expand on this, won’t you just get the original signal back if you recombine them?
If the rectifier is built with ideal diodes, yes, you get your original signal back.
But there is no such thing as ideal diodes. So you get crossover distortion.

You could even build this as a little cable with a lump in the middle, with the circuit below. Notice the distortion is worse with a 2Vpp signal than a 5Vpp signal. If you want to make it a little milder, replace the diodes with Schottkys, such as BAT54.

Crossover distortion.PNG
Crossover distortion 5V.PNG
I can imagine that this would work very well - the sound would generated with each repeat down to to just the peaks of the original signal, and then those would disappear. It wouldn't give me much control over the distortion though.

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Re: Distortion in Delay Feedback Loop

Post by jorg » Tue Feb 18, 2020 10:59 am

suckerformimi wrote:
Fri Feb 14, 2020 9:35 pm
...It wouldn't give me much control over the distortion though.
Try this:
Crossover distortion v2.PNG
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