Patching a Chaos Generator with a Slew and a Pulse Wave

This patch tip is inspired by and indebted to Rob Hordijk, whose Nord Modular G2 Pages introduced me to the concept. Regrettably, that site appears to have been removed. My riff on this patch seems to work a little better for contemporary hardware modular synthesizers by working with sub-audio rate pulse waves and slews rather than audio rate squares and low-pass filters which fewer players will have available to use as dedicated chaos signal generators.

Chaos vs. Randomness in Mathematical and Musical Contexts

A fully random signal is non-deterministic. Traditionally, this type of signal would be derived from uniform noise like white or pink noise, and although those kinds of signals would have certain statistical characteristics, at any moment the signal is random. It won’t have apparent repetitions or discernible patterns.

Chaotic signals are different because they are complex and sensitive to their initial conditions, but they seem to react more slowly, evolve gradually, and sometimes get trapped into repeating or morphing patterns. This kind of signal is more musically useful and it’s also more fun to play since it doesn’t necessarily react immediately to changes but gives the performer control of the underlying voltage system. Chaotic signals offer a higher level design of a synthesizer patch and are an excellent technique to explore in modular synthesis.

Here’s a riff on a patch I first learned from Rob Hordijk’s Nord Modular site. You can patch a chaos generator with the following: a S&H, a square wave oscillator and a low pass filter.

Chaos Generator Patch

• Pulse wave LFO => Slew input
• Slew output => Sample and Hold (signal) input
• Slew output => Pulse wave frequency
• Timing pulse (e.g. a clock or manual gate) => Sample and Hold (hold input)

The sample and hold output is the chaotic signal. It may be useful to patch it to an oscillator’s pitch control so that the effect is easy to hear (especially while dialing in the settings since the chaos patch can freeze up in some settings— it relies on finding a range of “sweet spots” where it will be the most active).

Changing any of the parameters will have an effect on the apparent patterns of the chaos. It is typical for a chaos generator to create riffs, staircase shapes, wildly swinging voltages and more. Playing its input parameters in real time can become an interesting performance control as you attempt to navigate the chaos generator into and out of patterns— you may even choose to “lock it up” deliberately by moving beyond the ranges that keep the patch working.

What to Do with Chaos

Once you’re happy with the chaos signal, it can be routed to any parameters you desire. Keep in mind that different parameters will respond differently (e.g. logarithmic vs. exponential responses) and that some parameters will sound most dramatic in different ranges. Of course, the power of modular synthesis is that you can further process the chaotic signal and here are some patches that will reward further exploration:

• Slew the sample and hold output.
• Patch another slew between the first slew and feeding back the pulse wave frequency.
• Patch the chaos into an addressable sequencer such as the location input on Make Noise’s Rene. This allows another layer of control since the values in each location can be changed while the chaos is controlled in another part of the patch.