README.md

Wild Pebble

Still very much in Beta testing

A generative rhythm and melody organism for the Music Thing Modular Workshop Computer.

Inspired by the spirit of Jonah Senzel's Pet Rock.

Wild Pebble creates evolving rhythmic structures, quantised melodic patterns, drum voices, and modulation voltages that slowly transform over time while remaining musically connected.

The goal is not precise repeatability, but constrained musical evolution.

Features

Dual probabilistic trigger streams
Quantised melodic CV generation
Internal kick and snare percussion voices
Self-mutating sequence behaviour
Phrase replication and variation
Slowly evolving scale randomisation
Internal tension modulation
External or internal clocking
Swing timing modes
Low CPU usage

Outputs

Pulse Output 1

Primary rhythm stream.

Used internally to drive:

melodic progression
kick drum voice

Pulse Output 2

Derived companion rhythm stream.

Used internally to:

trigger the snare voice
create correlated rhythmic variation

CV Output 1

Quantised melodic pitch output.

Generated from evolving scale-constrained note sequences.

Wild Pebble slowly changes between related scales over time depending on mutation amount and switch mode, creating harmonic drift without fully losing musical coherence.

CV Output 2

Energy/tension modulation output.

A smoothed evolving modulation source derived from:

step energy
accent
internal tension state

Audio Output 1

Kick drum voice driven from the primary trigger stream.

Produces deep evolving bass drum patterns with long decaying tails and pitch movement tied to sequence accents.

Audio Output 2

Snare and percussion voice driven from the companion trigger stream.

Combines tonal percussion with noise elements for shifting rhythmic textures ranging from soft clicks to noisy snare bursts.

Controls

Main Knob

Controls internal clock speed.

Ignored when external clock is present.

Clock Range

Wild Pebble’s internal clock ranges from approximately:

~90 BPM at the slowest setting
to fast audio-rate adjacent rhythmic speeds at the highest setting

The clock is designed to move smoothly from slow generative sequencing into dense evolving percussion patterns.

Swing amount varies depending on switch mode and affects every second step of the internal clock.

X Knob

Controls rhythmic density.

Higher values increase trigger probability. The range of probability of a trigger is from 5% to almost 100% chance. I recommend starting with the knob at 12 o'clock

CV Input 1 modulates density.

Y Knob

Controls mutation intensity.

Higher values increase:

sequence mutation
melodic movement
scale changes
structural instability

CV Input 2 modulates mutation amount.

Switch Modes

Up

stable melodic motion
restrained mutation
slower harmonic movement
tighter rhythms

Middle

balanced mutation
moderate swing
evolving melodic variation
gradual harmonic drift

Down

aggressive mutation
strongest swing
wider melodic jumps
more active scale changes
denser companion rhythms

External Inputs

Pulse Input 1

External clock input.

Automatically overrides the internal clock while active.

Pulse Input 2

Freeze input.

While held high:

mutation is disabled
current structure is preserved

Clocking and playback continue normally.

LED Behaviour

Wild Pebble uses the Workshop Computer’s 6 LEDs as a live visualisation of rhythm, density, mutation, and system state.

LED	Function	Behaviour
LED 1	Main Trigger	Flashes when `PulseOut1` fires
LED 2	Density	Brightness follows Density control (`Knob X + CV1`)
LED 3	Mutation	Brightness follows Mutation amount (`Knob Y + CV2`)
LED 4	Energy	Displays smoothed internal energy/modulation level
LED 5	Clock Source	Fully lit when external clock is active
LED 6	Tension	Displays evolving internal tension state

Sequencing Behaviour

Wild Pebble continuously evolves using:

probabilistic trigger generation
constrained mutation resistance
phrase copying
harmonic rotation
evolving scale selection
tension cycling

The interaction between rhythm mutation, melodic drift, repeating phrases, and gradual scale movement creates patterns that evolve organically while remaining playable and musically usable.

Building

Requires:

Raspberry Pi Pico SDK
Workshop Computer framework

Typical build flow:

mkdir build
cd build
cmake ..
make

Philosophy

Wild Pebble is intended to feel less like a fixed sequencer and more like a small autonomous musical system.

The interaction between:

mutation
repetition
probability
tension
harmonic drift
evolving drum voices
slow scale randomisation

creates continuously shifting patterns that remain musically coherent and performance-friendly. Tension evolves slowly over time with one full cycle taking 1440 sequencer steps.

Wild Pebble contains an internal evolving energy system.

Each step in the sequence carries its own energy state which slowly changes over time through mutation, repetition, and interaction with the global tension cycle.

Energy influences:

modulation movement
rhythmic intensity
dynamic behaviour

Some parts of the sequence gradually become:

more active
more unstable
more forceful

while others become:

restrained
sparse
quieter

This creates long-term phrasing and shifting musical behaviour even when rhythmic structures repeat.

The smoothed Energy CV output exposes this evolving internal state to the outside patch, allowing Wild Pebble to animate filters, VCAs, LPGs, reverbs, FM depth, and other modulation destinations with continuously changing expressive movement.

Together with the slow tension cycle, the energy system helps Wild Pebble behave less like a traditional sequencer and more like a small autonomous musical organism.

LED 4 and 6 now display their respective states more clearly