Pseudo Rungler

Generative
Written By Peter Barata

Rob Hordijk (1958 to 2022) was a Dutch musician and instrument builder. He originally trained as a sculptor and jewellery maker, but by the late 1970s Hordijk was experimenting with electronic music/sound. He wanted to use electronics to shape sound as a sculptor would shape their material.

Hordijk wanted to build instruments that could be more than appliances. He wanted to build electronic collaborators. He wanted his instruments to have a certain level of mystery and for them to reveal themselves to musicians only after exploration. He believed an instrument should respond to a player the way they might improvise with a musical partner. He wanted to build electronic instruments that could offer something unexpected rather than always spitting out identical predefined patterns.

Chaos

In the 1980s Hordijk developed an interest in chaos theory.

Chaos is not randomness. Chaos is deterministic. Randomness means events that have no order, cannot be reproduced, and have no statistical relationship to each other. Chaos is fully deterministic, meaning that the same starting conditions will always produce the same result, but it is also extraordinarily sensitive to those starting conditions. A tiny change at the beginning can produce enormous differences later. This is the famous "butterfly effect."

A chaotic system tends to settle, temporarily, into stable states called attractors. These appear, in musical terms, as repeating patterns. Small changes to the input can shift the output from one attractor to another. Between stable states, the system can enter a transition phase that sounds like pure randomness, before settling into a new repeating pattern.

A circuit that emits chaotic behaviour can generate endless waveforms, short loops, rhythms, and melodic fragments.

The Rungler

The Rungler is Hordijk’s best-known, chaos-inspired circuit. It’s at the heart of the Benjolin and has inspired countless DIY derivatives. It is ideal for generating short stepped melodic patterns and CV modulations that mutate in an unpredictable but still deterministic fashion.

The basic outline of the Rungler is as follows: A sine-wave oscillator is used to clock a CMOS shift-register. A triangle-wave oscillator is used as that shift-register’s data source. The shift-register’s various outputs are then fed back into both oscillators’ FM inputs. The user has control over the rate of each oscillator and the amount of feedback going to each.

Each oscillator has a direct output. The shift-register provides stepped, smoothed, pulsed, and clock outputs. The smoothed output is a slewed version of the stepped output. The pulsed output is a gate signal derived from the stepped signal.

The shift-register’s tendency to either evolve or lock into a pattern can be controlled by a three-position mode switch on its data input. The switch’s settings are: random, sparse, and dense. Random produces noise-like textures. Sparse produces looping patterns useful for melodic pitch modulation. Dense produces continuously evolving non-repeating sequences.

Because a shift register’s current state depends on its previous state, and because the Rungler feeds its own output back into the oscillators that drive it, each new state is a function of the previous state plus the current knob positions. This is what makes the Rungler chaotic in the technical sense: it tends to settle into temporary balanced states (short looping patterns or textures), and a small nudge to any control will push it into a new balanced state, often by way of a brief unstable passage. Depending on how the oscillators and feedback are set, the Rungler can lock into a tight loop, drift through continuously mutating sequences, or hover in an in-between zone where patterns emerge, hold, and dissolve.

Basic S&H Based Rungler-like Patch:

Cascadia doesn’t have a shift-register, but you can make a Rungler-like patch with the sample-and-hold instead. The basic core of the patch remains the same. Use one oscillator to clock the S&H, and a second oscillator as the data source. Mult the S&H output to two different VCAs. From the VCAs patch back into each oscillators’ inputs. The user has control over each oscillators’ rate, and the amount of feedback going from the S&H back to each oscillator.

Switch VCO-B pitch to ‘B’ only.

Patch VCO-B sine out to S&H clock in.

Patch VCO-A triangle (from the mixer section) to S&H source in.

Create the feedback loops:

Patch the S&H out to the mult in.

Patch from the mult to VCO-A FM in. The FM slider now controls the amount of feedback.

VCO-B doesn’t have an FM in with a built-in VCA. So, go from the mult to VCA-B in. Set the VCA-B control switch to the up position. Then patch from the VCA output back to VCO-B pitch in. The VCA-B CV amount knob now controls the amount of feedback for VCO-B.

S&H Outputs:

The S&H output is normalled to the slew-limiter input.

Patch the slew output to mixer in 1.

Patch a mult out to mixer in 2.

Drone:

Make Cascadia drone by pushing the VCA-A level slider all the way up.

Play:

Experiment with different settings for everything. Small changes will create different patterns. This patch is great at creating noise, clicks and traditional ‘avant-garde’-like bleeps and squawks.

This patch is just a jumping off point. Use it as a base to start exploring from.

Optional:

Wave Folding:

Use Wave-folding for more timbres.

Patch the filter out to the wave folder in.

Patch any waveform from either VCO A or B to the wave folder fold input.

Turn up the VCA-A aux slider.

More Feedback:

Create a wider variety of textures by patching from the main out to other places in the circuit.

Patch from the main out to either the VCF FM in, wave folder fold amount, or VCA-B CV in.

Complex Modulation:

Sum two LFO outputs and patch the result to a VCF FM input, VCA-B CV in, or VCO-A index.

Envelope B:

Try using ENV-B as an oscillator and modulating its settings.

Download PDF

Portrait

Further Reading

Peter Barata
Next

808 Bass Drum