Cracking The Code on Complex Guitar Pedals

I am wondering how to use an audio signal to modulate knobs. I am sure there are some basic methods, but what sort of more creative signal flows are there?

A basic Audio signal from a guitar is obviously problematic, as it will only scale b/w about 1-2 out of 10. It is also too fast of a modulation source.

It would be nice to have a trigger generated from a string pluck that could reset an LFO or initiate an ADSR. (I am learning that this is one approach with its own limitations and benefits).

I find videos like this get my imagination going:

This article is helping me.

Which I found on this thread which is also helpful.

I am realizing that this approach is similar to compression where you rectify the signal in order to create a cv. Makes me wonder about the difference between modelling an analog circuit and just creating a digital form from scratch. I suppose that in many ways this node based programming is necessarily like modelling analog circuits.

I see here that the peak detector in this compressor is very mathematically intimidating for me.

It would be interesting if someone wants to pull a John Madden and markup this image with an iPad or something and explain what is happening.

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I’m a little confused by what it is you are looking for, but I’ll give it a try.

You should be able to simply attach them to the knob. Also, it might be fine to run the audio through a clamp expression to limit the signal to 0 to 1.

You can add as much gain as you like in Audulus, you just have to keep in mind that you also raise the noise floor. You can use cascaded EnvFollow nodes to get smoother modulation that still follows your signal.

Well, thinking in terms of constantly flowing signals is closer to circuitry than writing lines of code and then compiling them, yes. But analog circuit modeling requires a deeper understanding of the elements of circuitry that you don’t necessarily have to involve yourself with in Audulus. I don’t often think about resistance or capacitance when making a module in Audulus.

I’m not exactly sure where the compressor you got that picture from came from so it’s a little bit out of context, but it looks like it is an attack/release envelope that is made out of two filters so it has a nice non-linear curve.

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The picture is of the peak detector module in this compressor:

compressor.audulus (163.5 KB)

I like the simplicity of the older articles and appecriate grounding ideas like this in analog circuitry. Then I can understand the various applications for implementing a design in terms of a desired outcome, watching it develop in the hands of different people.

Having just made a “real” compressor, in this instance it may be helpful as I have not built anything at the node level in Audulus yet. The subject of sidechaining seems to help. But, then this is probably a computationally inefficient method, but I don’t know.

The clamping seems to work well. Adding modulation attenuation offset is kind of useful, but is it possible to amplify modulation signals, rather than just setting the range?

I am not sure if I did this clamping right.

You can also see there are a lot of EnvFollowers linked up. This you said would provide smoothing. How do you get something as smooth as an LFO at audio rates?


The signal at the top is ADC-> Envfollow, while the one underneath is ADC ->Enfollow ->Enfollow ->Enfollow ->Enfollow ->Enfollow ->Enfollow.

As things are happening so quickly it is hard to clearly see the effect.

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Oh yeah! I’m actually kind of curious, how does that one work? Like what are the circuits doing?

You could probably run the signal coming through the cascaded EnvFollow chain through a simple slew limiter (low pass filter with a ~.999 alpha) and get something slower moving.

You might also check out the super simple compressor in the module library under effects>dynamics. It’s one of my designs, and I actually developed it to create enveloped control voltage based on a guitar signal.

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I worked off of this design.

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So from my understanding, we need a really tight “Auto-Wah” module, which could be modeled from you super simple compressor.

That is, being able to draw smooth modulation source curves for feeding knobs seems like an indespensible tool for getting the kind of functionality you see in the Chase Bliss pedals.

This way, we have a tool that is not buried in a single effect, but is available to use on existing projects and future applications.

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audio triggered envelope.audulus (26.7 KB)

Ok, so I separated the control voltage from the compressor. Now it’s like rectifying the wave, and setting a comparator to a certain volume. Then running the comparator signal through a slew to create a smooth CV.

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Awsome! This could get documented and posted as an effect tool for sure.

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Looks good!

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Auto-wahs are best done digitally with audio-triggered envelopes like @robertsyrett pointed out. The problem is just that you’ll be introducing noise modulation to the filter that isn’t ideal. I might be wrong but I think it’s easier to get the smoothing in the analog realm from the analog filters, or the way that an analog filter responds to those little remnant noisy peaks sounds less “crunchy.”

Do you mean analog modeled filters or hardware?

Hardware - generally they do better with high frequency noise modulation

Out of the question here. :grin:

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Yeah so what I’m saying is using an envelope based one will give you a cleaner sound than an envelope-follower based on will.

You mean trigger an EG module with the audio signal?

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Yes, like this one!

Envelope Follower.audulus (94.9 KB)

Using this kind of design also gives you more flexibility as to how the filter sounds.

That’s great thanks. At the same time I feel like they are two different approaches and that there are still great applications for the other Auto-Wah. While distortion in modulation that is too dynamic becomes unusable, some slightly variable noise in the modulation signal can retain a bit of the guitar feel, rather than it being too much like a synthesizer. But I could be wrong, I will have to do some testing.

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In fact my guess is the only reason why most Auto-Wahs don’t have more envelope control is because it just adds more circuitry and expense to the pedal. An ADSR, especially in the old days, would have taken up several square inches of board just by itself.