Emulating Hardware Effects

Hi all, I’m Restart and I’m an Audulus user since more than 3 years ago, maybe someone remembers me because i had some crazy ideas (and crazy hair right now) for making modules, and I want to restart doing them but before all I want something simplier (I hope).
I’m guitar and bass player, so I would like to use Audulus as my effect station. My idea is to use this midi interface : Sin%20t%C3%ADtulo and control with it the effects in audulus while I’m playing live with the instrument. I could emulate some simple effects but I want more (allways moreeeee) and I had a thought: If I know how to emulate what the basic electronic components (resistor, capacitor, diode…) do in an audio signal, I could make any emulation of any effect following the diagrams that are in the internet, such as this

So… can anyone help me explaining (with examples in audulus if possible) what the electronic components of guitar effect pedals does? I think that if we get this it could be a nice claim for audulus, because as me there are many people that don’t like the limitations and sounds of msot of the apps out there.
Many (men e.?) thanks and sorry for my poor english.


You don’t need to emulate individual components in Audulus, but you can take the block diagram as a guide to creating your stompboxes. This is a distortion pedal, so it has a portion of the pedal that is circled there with some arrows which is a transistor (a JFET maybe? i forget). So what happens is you’re amplifying the signal going into a transistor which gets saturated at a certain loudness and won’t get any more loud - that’s when it bends the sound into more of a square-like wave, cutting off the tops. I think you could get a somewhat similar sound with the JFET VCA here:

The tone controls you’d have to look up the ranges they cover, or just tune them, but my guess is it’s a highpass filter? In that case you can just implement a simple highpass after the drive section.

I’m not sure exactly how the sustain section works, but my guess is the sound kinda cuts off after it gets too low, so more sustain would allow more volume through (probably just another name for distortion control?)

You can disregard the bypass sections at the bottom - that would be just a button in the C input of a crossfade node where the effect is going into input A and the audio passing through the effect would be sent over and plugged into input B - that way the button would switch between the effect and dry signal.


All the transistors are bipolar. In this circuit the distortion is created by the pairs of 1N4148 diodes connected to T2 and T3. The diodes form part of a feedback circuit that alters the response of each amplifier stage by clipping the peaks from the signal. There is an RC filtered feedback loop on each stage as well. The sustain control adjusts the preamp stage gain which, when high, pushes the T2/T3 amp circuit into clipping. The tone control is a 12db/oct RC bandpass filter which is followed by a final amplifier stage and output volume control.

So essentially you have a diode clipper followed by an adjustable filter and a volume control. @biminiroad is in the midst of a refresh of the library and recently posted a demo of an excellent diode VCA:

This, followed by the filter of your choice, would be a better way to build an effect than trying to model a circuit component by component. It is difficult to model active components such as diodes and transistors accurately and creating a model of several connected in complex ways is computationally difficult. You would quickly run out of CPU. The best approach is to figure out the key component that is creating the effect and model that.


I think that is the key here with most of the work. As I am sure you know, with guitar pedals, various factors for why certain parts are used have very little to do with focused engineering, and more to do with what is available and what physically interfaces with what in order to deliver something that fits the market value.

When you approach effects from scratch in Audulus, treating tonal preferences as guidelines, it seems to shine best by being a platform that encourages intimate interaction and exploration of the rich appreciation of detail. It seems to take a while to acquire the knowledge to see this but it also develops the ear that can hear the differences.

Making the claim that a software plugin can emulate an analog through hole circuit gets a lot of attention, but it seems that over the last decade people have figured out when it is best to implement digital algorithms and when you would rather listen to the electricity perform live. There seem to be many more happy accidents in the analog realm, but when you get Audulus involved in a supportive role you can track the accidents, manipulate certain elements, or even work with lesser digital versions in order to move quickly and learn fast without buying a bunch of gear and then selling it.

Lastly, there was a move to get rid of gear and do it all with software. This came and left and we are now somewhere in the middle of the rebalanced appreciation for well designed physical musical tools/instruments that should stand as timeless, achievements – like classic cars.

Oh and, of course, the processing power necessary to run the delays, reverbs, etc. (of the quality that is even close to pedals) quickly creates problems for iPads. It can be a great compliment, but ultimately not a great candidate for replacing a pedal board. At least with the apps that are even attempting this, you have dedicated guitar focused DSP work that has being going on for years, and a platform that is set up to compliment all of the processing challenges involved. That is probably why there are limitations. Multiple modulations slow everything down.

Okay, but that being said, here is a practical thread if it is of any use to you:


It’s also true that many of today’s pedals are digital in nature or a blend of analog and digital circuits. My son has several Strymon units and they all incorporate at least some digital circuitry. Of course even though they have much less powerful CPUs than an iPad, they also have much less to do. The biggest challenge I see with using a Audulus as a pedal board is that all of the effects would be running at once since there’s currently no way to shut down parts of a patch. You can build some pretty nice effects with Audulus but it might be too much CPU to run more than a couple. Still, I use a BIAS BT-4 MIDI foot pedal with Audulus on my Air 2 and I’ve gotten some neat sounds