Sequencing & Clock

Random

Random CV generator — the modular synth answer to "what if the patch made up its own mind?".

What is a Random?

A random CV generator is the modular synthesizer's source of controlled chaos. At its heart is a simple idea: every time it gets clocked, it picks a new random number and outputs that number as a control voltage. Send that voltage to a VCO and the pitch jumps somewhere new. Send it to a filter cutoff and the timbre wanders. Send it to a VCA and the volume flickers. The patch starts making decisions you didn't tell it to make.

Random CV traces straight back to Don Buchla's 266 Source of Uncertainty from 1981, which dedicated an entire module to noise, sample-and-hold, and stochastic voltage. The Make Noise Wogglebug (2009) updated the idea for Eurorack, and the Mutable Instruments Marbles (2018) — see MI-Marbles — turned it into a full stochastic music workstation. The lineage is aleatoric music with knobs.

The cleverness in modern random modules is in interpolation. A bare random module gives you stepped output: instant jumps between values. But the same random sequence interpolated linearly gives you ramps; interpolated with cosine curves gives you smooth wandering modulation; interpolated with exponential curves gives you sharp percussive swoops. One random source, four flavors of randomness — from twitchy to organic — running in parallel. They are mathematically the same sequence; what differs is how the output morphs between values.

The other essential control is probability. At 100% every clock pulse generates a new value. At 50% half of the pulses are skipped — the previous value holds. At 0% nothing changes. Probability transforms a generator from "new note every step" into "sometimes a new note, sometimes a repeat", which is what makes it sound like music rather than dice rolls.

Our Random

Our Random is 10 HP with four simultaneous outputs from a single random sequence: STEP (sample-and-hold), LIN (linear ramp), SMTH (cosine interpolation), and EXP (exponential curve). They are all the same underlying values; what differs is the morph between them, so you can patch the smooth output to a filter and the stepped output to pitch and they will move together.

The internal clock is 0.01 to 100 Hz on an exponential scale, with 1V/Oct tracking on the rate CV input — a +1V doubles the rate, just like a VCO. Patch an external clock to TRIG and the internal clock yields automatically. Probability is 0 to 1, with CV modulation; we add the CV to the knob value so a +0.3V offset shifts probability up by 30%.

Range (0V to 10V) sets how far the values can swing, and the Offset toggle picks unipolar (0V to +Range) or bipolar (-Range/2 to +Range/2) — important because pitch CV usually wants unipolar (positive only) but modulation usually wants bipolar (positive and negative). The dedicated TRIG OUT fires on every value change, so you can drive an ADSR exactly when a new note appears.

In a patch

The most common use is generative pitch. Random stepped output → quantizer → VCO V/Oct gives you a melody that is unpredictable but always in scale. Add a clock to TRIG so the random voltage updates in time with the rest of the patch, and you have a generative sequencer in three modules.

For modulation rather than pitch, use the smooth output. Patched into filter cutoff or oscillator FM amount it produces slow organic drift — the patch breathes instead of staying static. The exponential output is good for rhythmic accent: through a VCA it creates per-step volume variation that sounds more like a drummer's dynamics than a stiff sequencer.

Random CV plays nicely with Bernoulli gates (random gate routing) and Marbles (full stochastic sequencer). For mathematically structured rhythm rather than pure randomness, use a Euclidean generator. Random CV is for unbiased uniform noise; the others impose specific structure.

Inputs

RATE (cv) — CV modulation for the internal clock rate. Tracks 1V/oct - higher voltage means faster rate.
PROB (cv) — CV modulation for probability. Added to the Prob knob value.
TRIG (gate) — External trigger input. When patched, overrides the internal clock. Each rising edge generates a new random value (subject to probability).

Outputs

STEP (cv) — Stepped random output (sample-and-hold). Jumps instantly to each new value. Classic S&H behavior.
LIN (cv) — Linear random output. Ramps in a straight line from the previous value to the new one.
SMTH (cv) — Smooth random output. Uses cosine interpolation for gentle S-curve transitions. The most musical and organic-sounding output.
EXP (cv) — Exponential random output. Fast attack, slow decay - creates sharp swoops. Great for percussive or accent-like modulation.
TRIG (gate) — Trigger output. Fires a short pulse every time a new random value is actually generated (respects probability).

Controls

Rate — Internal clock rate (0.01 to 100 Hz). Controls how often a new random value is generated. Only active when no external trigger is patched.
Prob — Probability of generating a new value (0 to 1). At 1.0, every trigger makes a new value. At 0.5, half the triggers are skipped. At 0, values never change.
Range — Voltage range of the output (0 to 10V). Controls how far the random values can swing.
Offset — Unipolar/bipolar toggle. Unipolar outputs 0V to +Range. Bipolar outputs -Range/2 to +Range/2.

Inspired by

The lineage of randomness in modular runs from Don Buchla's 266 Source of Uncertainty (1981) through Make Noise's Wogglebug to the Mutable Instruments Marbles. Four simultaneous interpolation outputs (stepped, linear, smooth, exponential) cover the full range from classic sample-and-hold to slow drift in one module.

Mutable Instruments Marbles
Buchla 266 Source of Uncertainty
Wogglebug

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