| project name: | grurder |
| project url: | https://github.com/icco/grurder |
| author: | icco |
| description: | generative dual-voice MIDI sequencer with Euclidean rhythms and Turing Machine melodies |
| documentation url: | https://github.com/icco/grurder/blob/main/README.md |
| tags: | sequencer midi generative euclidean |
grurder
A generative MIDI sequencer for monome norns. Takes input from an 8mu and outputs two evolving melodic voices to eurorack via mmMidi (or any MIDI-capable module).
Hardware
- norns (or norns shield)
- 8mu — 8-fader MIDI controller with accelerometer (optional but recommended)
- mmMidi or any MIDI-to-CV module
Install
;install https://github.com/icco/grurder
What it does
Two independent voices, each with their own rhythm and melody generation. Rhythms come from Euclidean patterns[^1] — distribute some pulses across some steps and you get patterns that show up all over world music. Pitch comes from a shift register inspired by the Turing Machine[^2] — a 16-bit loop that drifts based on a probability knob:
- Prob 0: locked repeating melody
- Prob 1: fully random
- In between: gradual drift
Both voices share scale, root, and octave range but have independent registers and patterns.
8mu mapping
Faders (CC 34–41)
| Fader | Sequence | Parameter | Range |
|---|---|---|---|
| 1 | Seq 1 | Step count | 4–16 |
| 2 | Seq 1 | Pulse count | 1–steps |
| 3 | Seq 1 | Rotation | 0–steps-1 |
| 4 | Seq 1 | Flip probability | 0–1 |
| 5 | Seq 2 | Step count | 4–16 |
| 6 | Seq 2 | Pulse count | 1–steps |
| 7 | Seq 2 | Rotation | 0–steps-1 |
| 8 | Seq 2 | Flip probability | 0–1 |
Tilt (accelerometer)
The 8mu's accelerometer controls MIDI velocity for each voice. Configure your 8mu to send tilt on CC 14 (X-axis → seq 1 velocity) and CC 15 (Y-axis → seq 2 velocity) via the 8mu web editor. Tilt maps to a velocity range of 30–127. Without tilt input, velocity defaults to 100.
Buttons
| Button | Action |
|---|---|
| A (C2) | Reset both sequences |
| B (C3) | Randomize pitch registers |
| C (C4) | Toggle seq 1 mute |
| D (C5) | Toggle seq 2 mute |
Norns controls
Works fine without an 8mu:
- E1: Tempo
- E2: Octave range (1–4)
- E3: Root note
- K2: Toggle sequence view / fader view
- K3 short: Reset sequences
- K3 long: Randomize pitch registers
Screens
Sequence view (default): Two lanes showing recent note history. Height = pitch, brightness and bar size = velocity, with the current step brightest. Dots along the bottom show the Euclidean pattern. Header shows root, scale, tempo, octave range, and current velocity for each voice.
Fader view: Eight vertical bars showing the 8mu CC values (stp/pls/rot/prb per sequence), plus velocity readouts and horizontal tilt bars at the bottom.
MIDI output
- Voice 1 → MIDI channel 1
- Voice 2 → MIDI channel 2
- Velocity controlled by 8mu tilt (defaults to 100 if no tilt input)
Params menu
- midi in — input device (default port 1)
- midi out — output device (default port 2)
- scale — major, minor, major pent, minor pent, dorian, phrygian, lydian, mixolydian
License
MIT
[^1]: Godfried Toussaint, "The Euclidean Algorithm Generates Traditional Musical Rhythms" (2005) [^2]: Tom Whitwell / Music Thing Modular, Turing Machine