Thorns

Fractal MIDI sequencer for norns + grid

Requirements

• norns (any version)
• Grid (16x8 minimum)
• MIDI output device

Features

• Monophonic step sequencer (2-16 steps)
• Binary transformation tree with 7 levels of depth
• Five transformation types:
  • Pitch modification (nonlinear power function)
  • Velocity modification (nonlinear power function)
  • Mutate (±1 semitone shifts)
  • Gate chaos (mute/unmute/create notes)
  • Time shift (rotate pattern forward/backward)
• Real-time path navigation through transformation space
• Scale quantization
• Grid-based editing with octave windows
• Separate gate/pitch and velocity editing screens
• Audio engine (PolyPerc) or MIDI output

Controls

Encoders

• E1: Branches (tree depth: 0-7)
• E2: Path (navigate variations: 0.0-0.99)
• E3: Tempo (20-300 BPM)

Keys

• K2: Play/Stop
• K3: Toggle gate/pitch ↔ velocity screen (edit mode only)

Key Combinations

• K1+E1: Shift octave window (edit mode)
• K1+E2: Change pattern length (2-16 steps)

Grid

Edit Mode (Stopped):

• Screen 1 (Gate/Pitch): Click cells to set/clear notes
  • Columns = steps (1-16)
  • Rows = pitches (8 visible at a time from 3-octave range)
  • Scale degrees shown dimly
• Screen 2 (Velocity): Click column to set velocity height
  • Vertical bar height = velocity (8 levels)

Play Mode:

• Displays currently playing transformed sequence
• Current step highlighted
• Shows notes in current octave window

Parameters Menu

• Output Mode: Audio / MIDI / Both (default: Audio)
• Base Pitch: Root note of the 3-octave range (C0-C4)
• Scale: Quantization scale (Major, Minor, Dorian, etc.)
• Transformations:
  • Pitch Mod: Enable/disable pitch modification (default: On)
  • Velocity Mod: Enable/disable velocity modification (default: On)
  • Mutate: Enable/disable mutation (default: On)
  • Gate Chaos: Enable/disable gate chaos (default: On)
  • Time Shift: Enable/disable time shift rotation (default: On)
• Gate Chaos Probability: Chance per step for gate chaos (0.0-1.0, default 0.05)
• Mutation Probability: Chance per step for mutation (0.0-1.0, default 0.5)
• Shift Freedom: Controls time shift distribution (0.0-1.0, default 0.5)
  • 0.0: no shifting (always stays in place)
  • 1.0: all shifts equally likely (uniform distribution)
  • 0.0-1.0: favors smaller shifts
• Audio Engine:
  • Release: Note release time (0.1-5.0s, default 0.5)
  • Cutoff: Filter cutoff frequency (50-5000Hz, default 1000)
  • Gain: Output gain (0.0-4.0, default 1.0)
• MIDI Output Channel: 1-16
• MIDI Device: Virtual or hardware device
• Clock Source: Internal (only)

How It Works

Pitch Range

• 24 semitones total: 8 below base pitch to 15 above
• Displayed in 3 windows of 8 semitones each
• Input is chromatic (all 24 semitones available)
• Output is quantized to selected scale

Transformation Tree

When you hit play with a modified trunk:

1. Generates a complete 7-level binary tree
2. At each branch level, randomly selects from enabled transformation pairs
3. Pre-generates all random values (so playback is deterministic)
4. Stores full sequences at every node

You can enable/disable individual transformations in PARAMS to control which types are used in the tree. If all transformations are disabled, only the trunk plays.

Playback

• Path parameter (0.0-0.99) determines which branch to follow at each level
• Path value is decomposed into binary choices (left/right at each level)
• Plays trunk → level 1 → level 2 → … → level N (where N = Branches)
• Then loops back to trunk

Example: If Branches = 2 and Path = 0.3:

• Path 0.3 falls in range [0.25, 0.375) = binary “01”
• Playback sequence: trunk → left branch → right branch → loop

Transformations

1. Pitch Modification

• Nonlinear pitch transformation using power function
• For each note: r = pitch relative to base (-8 to 15), p = (r - 3.5) / 12
• Random exponent g between 1 and 2
• If p > 0: transformed_p = p^g
• If p < 0: transformed_p = -(-p)^g
• Transform back: r = 3.5 + 12 × transformed_p
• Branch A: uses exponent g (expands high/low ranges)
• Branch B: uses exponent 1/g (compresses toward center)

2. Velocity Modification

• Nonlinear velocity transformation using power function
• For each note: v = velocity (0-127), p = (v - 63.5) / 64
• Random exponent g between 1 and 10
• If p > 0: transformed_p = p^g
• If p < 0: transformed_p = -(-p)^g
• Transform back: v = 63.5 + 64 × transformed_p
• Branch A: uses exponent g (expands dynamic range)
• Branch B: uses exponent 1/g (compresses toward middle velocity)

3. Mutate

• Randomly shifts both pitch and velocity for each step
• Pitch: shifts by -1, 0, or +1 semitone with probabilities: -1 (p/2), 0 (1-p), +1 (p/2) where p = mutation probability
• Pitch bounces off range limits (-8 to +15 semitones relative to base pitch)
• Velocity: shifts by -8, 0, or +8 units with same probability distribution
• Velocity wraps around range (1-127)
• Branch A: Apply shifts as generated
• Branch B: Apply negated shifts

4. Gate Chaos

• Each step has probability p (gate chaos probability) to:
  • If gate on: turn off
  • If gate off but was originally on: turn on
  • If gate off and was never on: create new random note
• Both branches apply same logic to same steps

5. Time Shift

• Shifts pattern by m steps where m is chosen from 0 to pattern_length using weighted distribution
• Distribution: P(m) = x^m · (x-1)/(x^(n+1)-1) where x = shift_freedom parameter
• Special case: if m = pattern_length, reverse the sequence instead of rotating
• Branch A: Rotate forward by m steps (or reverse if m = n)
• Branch B: Rotate backward by m steps (or reverse if m = n - reverse is its own inverse)
• Shift freedom controls distribution:
  • x = 0: always m = 0 (no shift)
  • x = 1: uniform distribution over all m
  • 0 < x < 1: favors smaller shifts
• Preserves all note data, changes timing/position/order

All random values are pre-generated when tree is built, so the same path always produces the same result.

Installation

1. Copy the thorns folder to ~/dust/code/
2. Restart norns or run SYSTEM > RESTART from the norns menu
3. Select THORNS from the norns script selection

Tips

• Start with Branches = 0 to just hear your trunk pattern with scale quantization
• Increase Branches gradually to explore deeper transformations
• Sweep Path slowly to hear smooth transitions through transformation space
• Use short patterns (4-8 steps) for rhythmic variation
• Use longer patterns (12-16 steps) for melodic development
• Try different scales - quantization happens at output, so transformations work in chromatic space
• Adjust transformation probabilities (Gate Chaos, Mutation) and Shift Freedom to taste
• Enable/disable specific transformations in PARAMS to isolate their effects
• Lower Shift Freedom (< 0.3) for subtle rhythmic variations
• Higher Shift Freedom (> 0.7) for more dramatic pattern rearrangement

Credits

Inspired by Qu-Bit Electronix Bloom hardware sequencer. This is an independent implementation with different features and approach. Not affiliated with or endorsed by Qu-Bit Electronix.

Built for norns.

License

Copyright (c) 2025 Marc Pelath

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.