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  • Writer's pictureLeonardo

Caudal is making some chaos

If you have been reading this blog, you may know that I have made multiple prototypes of Caudal. The first revision I made was in 2019 and I have been forced to do major changes due to variety of issues. Almost four years later the hardware version of Caudal is almost here. If you want to get one, you can enable the "Notify When Available" feature in the product page:

Caudal is a module that generates chaotic signals based on the simulation of physical systems. The original model was the four segment pendulum. This system produces signals that are chaotic but have some level of correlation. Compared to random signals, the pendulum model tends to be more harmonious.

You can check the video I made when the software version was released.

Some time after I added new simulations: the four body problem and a fish tank. The four-body problem simulates four planets and their interaction due to gravity. The fish tank is my idea on how fish would navigate around their tank based on simple rules. These three models behave differently but they are equally useful.

Differences between the hardware and software

The Caudal hardware has the following differences compared to the software version:

The “angle” outputs were removed due to lack of space. Instead of having 12 outputs the hardware has 8. I added a builtin sample and hold for each of the two groups (X and Y) of outputs.

All the other features are similar. You can reverse, hit, store and recall the state of the module.

In this initial version of the firmware I have added a fourth mode based on the Buchla source of uncertainty. Caudal has four generators of “fluctuation random voltages”. The Speed and Energy knobs allow to control the frequency and “noisiness” of the voltages. These voltages are sent to the X outputs while the Y outputs generate pulses.

If you don’t know what to do with a module like this here are a few examples. I have asked my friend Rolf Kasten, who has written a very extensive book on generative music, to send me some didactic examples of Caudal in action.

These examples are made with VCV Rack so you will be able of following them even without having the hardware.

But first, here's a patch I made that is fully orchestrated by Caudal.

Examples by Rolf Kasten

So, let me talk about Caudal a bit now. First of all: Caudal is not a generator of random cv, it's not random, it's chaotic. I hear you saying: “Hey, that's the same, isn't it?” Well, it's not. Take the following little patch (“caudal_p1.vcv”, the files can be downloaded below) comparing the output of a S&H module with Caudal's output and you see the differences.

Download ZIP • 15KB

There are two main differences of musical importance: the CV development which is delivered by Caudal is continuous and not stepped, and it has a whiff of regularity, meaning: there seem to shine a kind of pattern through the chaotic movements, like a bundle of sun-beams shining through the roof of leaves, which are moving in a light summer breeze in the forest. In my trilogy about making generative music I'm talking of (and explaining) different characters of randomness and how to make use of them (see

And as Caudal offers 4 different grades of chaos the module invites us to compare and contrast them. Let's have a look at a couple of patches now. The first patch and preset is called “caudal_1.vcv”. The 4 X outputs modulate the pitch of Basal modules, whereas the 4 Y outputs modulate the timbre.

The 4 voices are all based on the same pentatonic scale, so that we can nicely hear how the different “grades of chaos” generate 4 different characters of melodies, which together make a complex sounding polyphonic sound carpet, which nevertheless sounds rather harmonic. 4 slightly different envelopes emphasise the different melodies, and a bit of reverb makes it all sound even nicer. The parameters SPEED and ENERGY are modulated by an LFO-S&H block to bring even more variability to the overall result. The following video shows the patch.

The following patch is a bit more complex. There are two melodies playing together. These two melodies are interrupted by a third melody. All 3 melodies are again based on the same pentatonic scale, but all three scales have different root notes – it shouldn't be a big surprise that these root notes are “C”, “F” and “G”. the patch and the preset are called “caudal_2.vcv”.

In this patch Caudal fulfills different tasks:

  • delivering pitch CV (red patch cables)

  • delivering timbre modulation (green patch cables)

  • switching the voices on and off and envelope gating (yellow patch cables)

  • modulating the delay time (blue patch cable – blue cables are also used for the audio path)

  • modulating itself (purple patch cables)

The colours of the two patch cables leading to the SCOPE in the lower row are without a certain meaning (there's no 6th colour in VCV Rack).

The sound of the 3 voices is generated by Basal, Bleak and the Macro Oscillator. Basal´s pitch development as well as its timbre modulation are smoothed out a bit by two Slew Limiters. I've done the same concerning the switching on and off of voice 3 (Bleak). The Slew Limiter in the upper row makes it more a fast blending in and blending out than a hard switching.

The pitch CV for voice 1 (Basal) is delivered by the sum of outputs AX and AY, voice 2 (Macro Oscillator) gets its pitch CV from output CX, and voice 3 (Bleak) is pitch modulated by output DX.

Voice 1 (Basal) is patched through a REVERB 1 module, voice 2 (Macro Oscillator) is send through a Delay, and only Bleak's voice, which is pitch modulated by the most “excentric” output of Caudal, is sent directly to the audio mixer.

Let's have a look at the mentioned switching mechanism. Caudal's outputs BX and BY send their CV to a logic module. From there (from the “OR” output) the gate signal for the envelope (voice 1 – Basal) is derived: always when at least one of the two Caudal outputs delivers the needed voltage of positive 2 Volt the envelope is roused, and the voice's VCA opens.

But from the same OR output there goes a patch cable to an inverter module, which makes a positive signal negative and vice versa. Let me mention that the logic module puts out either zero volt or plus ten volt. Having mentioned this I may explain the function of the Atenuverter module now. The mentioned inverter spits out zero Volt, when it gets zero Volt, and it delivers minus ten Volt,when it gets plus ten Volt. But zero Volt as well as minus ten Volt doesn´t rouse either an envelope nor opens a mixer channel. What I need is zero Volt (when the OR output delivers plus 10 Volt) and plus 10 Volt, when the OR output delivers zero Volt. Therefore I add plus 10 Volt (Atenuverter) to the inverter´s output and patch the resulting CV to the mixer channels (channel 3) fader CV.

The following video shows the whole patch.

Let´s do something simpler (but not less interesting) again. In the following patch (and preset), which is called “caudal_3.vcv” (what a surprise!:-)) I compare Caudal´s chaotic output with the output of a S&H module.

There are two voices, both generated by Basal modules. Voice 1 (left Basal) is pitch modulated by Caudal (through an attenuating VCA and a quantiser). Voice 2 (right Basal) is pitch modulated by the S&H module (again through a VCA-Quantiser block whith the same adjustments as at voice 1).

The quantiser is triggered by Caudal´s positive CV (always when the Scope´s curve crosses the zero Volt line coming from negative voltages a new pitch CV for voice 2 is generated). The video shows the patch, and the preset invites for experiments of your own.

The last patch and preset (“caudal_4.vcv”) is again a simple one. Here I make use of the fact that Caudal´s CV outputs deliver smooth continuous developments instead of CV steps.

The S&H generates the pitch development, but the smooth CV from Caudal modulates the timbre generating brass like sounds. The following picture shows the little patch.

I have used only one of the three basic algorithms of Caudal (the multi segment pendulum algorithm) here. Each of the three algorithms deliver different characters of “chaos” (see my introducing words and my website to learn more about this matter).

Let me say “Thank you” to Vult for making this versatile (not “random” but “chaotic”) CV generating module.

Cheers and Peace!

Enjoy your day!


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