Plainsound Hexatone

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Try the dev branch

User Manual

Developer Quickstart

Designed by Siemen Terpstra in the late 1980s, based on Erv Wilson's microtonal keyboard designs (1967-), inspired by R.H.M. Bosanquet's Generalised Keyboard (1873) and Ivo Salzinger's Tastatura Nova Perfecta (1721).

Initial development by James Fenn with additions and modifications from Brandon Lewis, Bo Constantinsen, Chengu Wang, Ashton Snelgrove. Sampling credits to Scott Thompson, Tim Kahn, Carlos Vaquero, Dr. Ozan Yarman, Lars Palo, Soni Musicae.

MIDI version designed and programmed by Marc Sabat. Current dev version 3.2.0-beta.2 (May 2026), released as Free/Libre and Open Source Software under GPL-3.0. Current stable release: 3.1.0. Code on github: https://github.com/PLAINSOUND/hexatone. Discord: https://discord.gg/NGVTmDFPtf.

Current State

Hexatone 3.2.0-beta.2 is a live microtonal keyboard and scale workspace built around:

• isomorphic hexagonal layout
• rational / just intonation with automatic HEJI notation
• built-in tunings, Scala import/export, and user presets
• scale editing, including note names and colours
• live retuning of scale degrees and reference frequency
• rationalisation and modulation
• MPE-aware MIDI input with automatic mapping of 2D controller geometries
• MIDI Output (MTS and MPE)
• snapshots for comparing chords and tunings

PLAINSOUND HEXATONE can be used entirely in the browser:

• input with mouse / touch / computer keyboard
• output using built-in samples
• SUSTAIN, OCT, MOD controls
• retuning and scale editing using drag and drop
• scale rationalisation to user chosen parameters
• snapshots

Hexatone also supports:

• WebMIDI with optional SysEx
• MIDI input mapped either to the chosen hex layout or to nearest scale degree
• controller recognition and geometry-aware mapping
• LED feedback on supported controllers
• MTS and MPE output routings
• OSC -> SuperCollider output through a local bridge in a cloned repo

Hexatone is a live performance and composition companion to Scale Workshop.

See also usermanual.md.
For local setup and development commands, see DEVELOPER_QUICKSTART.md.

Isomorphic Keyboards

Wikipedia

The Music Notation Project Wiki

AltKeyboards

Version history

3.2.0-beta.2 (currently in development)

Live performance architecture

• architectural separation of Keys into smaller runtime modules, moving MIDI input, expression handling, snapshots, MTS output, controller maps, and settings-impact classification out of the canvas path
• reduced full Keys reconstruction to true tuning/layout changes; most live performance settings, including MIDI input device now update through targeted runtime paths instead of interrupting the keyboard
• controller geometry changes now rebuild only the controller map, preserving the active Keys runtime

Controller and LED feedback refinements

• refined Auto Send Colours for Lumatone, Exquis, and LinnStrument
• improved Lumatone, Exquis, and LinnStrument output-port matching
• expanded LinnStrument User Firmware response shaping:
  • X Spike Reduction for rejecting noisy raw X excursions under light pressure
  • X Input Smoothing for event-driven per-pad smoothing without requestAnimationFrame or timer dependence
  • Row Glide Shaping for moving between near-linear glide and more quantised row transitions
  • cleaner note attack and release behavior through temporary note-on quantise assist and low-pressure release hold

Scale workspace and rationalisation

• exact interval parsing and workspace groundwork
• rationalisation integrated into the scale-table workflow
• support for exact ratios, cents, and EDO steps in the scale table
• clearer distinction between preserving existing ratios and re-searching a scale from pitch targets
• scale-size growth pads new degrees by repeating the equave, inheriting degree-0 names and colours
• Sort Degrees Ascending reorders interior scale degrees
• interior scale degrees can now be drag-reordered or deleted directly by clicking the degree

Live tuning workflow

• live retuning of individual degrees and reference frequency
• smooth compare/save/revert tuning workflow
• snapshots for capturing and replaying absolute-pitch chords across tuning changes
• sustain/latch and OCT controls for live testing and performance

Notation and JI direction

• HEJI and reference-frame groundwork in the notation layer
• increasing emphasis on exact interval identity and rational interpretation
• JI Modulation fronm a source note to a target with handoff, tracked in a Modulation History palette

MIDI / controller system

• WebMIDI permissions are user-selectable; SysEx is optional
• controller-aware geometry mapping and manual override
• input modes for:
  • MIDI to hex layout
  • MIDI to nearest scale degree
• MPE input and expression support
• LED-capable controller integration

Outputs

• built-in sample synth
• MTS Real-Time MIDI
• MTS bulk-dump tuning-map
• MPE
• OSC -> SuperCollider via local yarn osc-bridge

Controller status

Supported or actively integrated controllers include:

• Lumatone
• Exquis
• LinnStrument
• Tonal Plexus
• C-Thru AXIS-49
• TS41 MIDI Keyboard

Other controller paths remain exploratory or less tested.

Local development

yarn install
yarn start

Useful commands:

yarn test
yarn start
yarn build
yarn osc-bridge

3.1 (April 2026)

WebMIDI and Sysex made User-Selectable

Controller database reactivity based on mode 2D geometry or bypass

TuneCell smoothing rebuilt

MIDI input — scale target mode: new Input Mode selector in MIDI settings: MIDI to Hex Layout (existing behaviour) or MIDI to Nearest Scale Degree. In scale mode, incoming MIDI pitch is matched to the closest degree of the active scale by cent distance, across any tuning or equave. User-configurable tolerance (default 25¢) and out-of-tolerance behaviour (Accept Best / Discard). Geometry, anchor, and transposition controls are hidden when scale mode is active.

MTS output — Dynamic Bulk Dump: new transport mode for synths that accept MTS bulk dumps but not single-note real-time SysEx. On each note-on, the carrier slot is patched in a maintained 128-note map and the full dump is sent before triggering the note. Shares carrier selection and MTS encoding with the existing real-time mode.

MTS output — Centered Static Bulk Dump: the static 128-note map is now automatically centered around the screen's central degree (center_degree). The centering algorithm searches MIDI notes 57–72 (A3–C5) for the note whose 12-EDO pitch class best matches the central pitch, maximising usable keyboard coverage. Sustained notes are protected from mid-phrase map updates; Auto-Send option resends the map whenever relevant settings change.

Expression: mod wheel (CC1) is now routed to the sample synth's lowpass filter, matching the MPE slide (CC74) path. Channel pressure (aftertouch) now broadcasts to all sounding voices simultaneously by default (was recency-stack only). Both are also forwarded to MIDI and MPE outputs.

iOS fix: audio now starts on the first touch without requiring the refresh button.

Changed octave-to-equave hardcoded logic to allow user-specified behaviour for other scales (no transposition, transposition by a specified number of scale degrees, or by equave)

Independent retuneability of all scale degrees and reference

Fixed input interoperability logic (mouse, touch, computer keyboard, MIDI)

Added MPE input mode with per-voice pitch bend and pressure routing

Under the hood fixes: refactored persistence and loading logic. Preparing for integration of scale math with xen-devs.

Supported 2D isomorphic controller geometries (auto-detected by MIDI device name):

• Lumatone https://www.lumatone.io/ — 280-key isomorphic surface, 5 blocks × 56 keys, channels 1–5 encode block position (0-55)
• C-Thru AXIS-49 https://www.c-thru-music.com/cgi/?page=prod_axis-49 — 14×7 isomorphic hexes, selfless mode (ch 1, notes 1–98)
• TS41 MIDI Keyboard https://tristanbay.com/gear/ts41-midi-keyboard/ — 41-EDO Bosanquet layout, single channel (ch 1, notes 1–126)
• Exquis (Intuitive Instruments) https://dualo.com/en/welcome/ — 61-note isomorphic hex grid, Rainbow Layout (Preset 6), MPE output on ch 2–15
• Tonal Plexus https://hpi.zentral.zone/tonalplexus - (ch 3-14, layout for 205edo)

In progress but untested:

• C-Thru AXIS-64 — 16×8 variant of the AXIS-49 layout, not tested
• Roger Linn Design LinnStrument 128 — 16×8 grid, one row per channel (ch 1–8), full MPE support
• Ableton Push 2 / Push 3 — 8×8 isomorphic pad grid, single channel, default 4ths tuning
• Novation Launchpad (Pro / X / Mini mk3) — 8×8 grid in programmer mode

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3.0.2 (March 2026)

Major reactivity fixes; MTS & MPE functionality expanded; scale resizing and Divide Octave/Equave features.

3.0.1 (early 2026)

Updated UX; added latch sustain; moveable central scale degree.

Version 3.0.0 (early 2026)

Added Scala/JSON IO; user presets; polyphonic aftertouch response with built-in sounds.

Version 2 (2022–2026)

Marc Sabat forked Ashton Snelgrove's webpack rebuild with rudimentary MIDI and began Hexatone develpment fron the former "Terpstra Keyboard". Renaming to acknowledge Erv Wilson's central contribution to the hexagonal 2D layout. Added full MIDI input and output path; Lumatone plug-and-play compatibility with channels-to-equaves logic; reshaped built-in presets; user-switchable Built-In/MTS/normal MIDI output options. Added and edited samples.

Version 1 (2016)

Terpstra Keyboard — hexagonal keyboard proof of concept that helped kickstart the Lumatone.