MIDI Grid — accessible quick MIDI entry for REAPER

A grid / step-sequencer entry mode for REAPER's MIDI editor, built for keyboard-and-speech use with OSARA.

Left and right walk the timeline one grid cell at a time. Up and down walk the pitch axis by scale degree. Enter toggles a note in the current cell. Everything you land on is spoken and sounded, so you can hear what is already there as you move.

It is not a replacement for the MIDI editor. It is a fast way to block out a clip; switch grid mode off and OSARA's normal editing is right there, unchanged, on the same cursor.

Requirements

• REAPER
• OSARA — for speech output
• SWS — for the note-naming octave preference

No other extensions. No ReaPack, no js_ReaScriptAPI, no ReaImGui.

Install

Clone or download this repository anywhere you like, then:

1. Close REAPER completely. It rewrites reaper-kb.ini when it exits and will throw away anything written while it is running.

2. Run:

   powershell -ExecutionPolicy Bypass -File install.ps1
   

3. Start REAPER, select a MIDI item, press Alt+Shift+G.

You should hear something like "Grid mode on, C major, grid 1/16, hold off, C5, 1.1.00".

To remove it again: powershell -ExecutionPolicy Bypass -File install.ps1 -Uninstall

The installer backs up reaper-kb.ini to reaper-kb.ini.midigrid-backup before its first change, and is safe to re-run.

Why not "Import key map"?

MidiGrid.ReaperKeyMap is included for reference, but importing it does not reliably work, and the way it fails is silent and confusing: REAPER accepts the file, registers the script actions, and then converts every key binding it cannot resolve into a No-op (no action) entry. The keys appear bound in the action list but do nothing.

The cause is that a KEY line must reference the named command — the SCR id with a leading underscore (_RSmidigrid_open), not the bare id (RSmidigrid_open). install.ps1 writes the underscored form directly.

If you would rather not run a script, you can bind the ten MIDI Grid: actions by hand in Actions → Show action list. That always works.

Keys

Main section

Key	Action
Alt+Shift+G	Open selected item in grid mode

MIDI editor section

Key	Grid mode ON	Grid mode OFF (passes through to)
Left / Right	Cursor back / forward one grid cell	OSARA previous / next chord
Up / Down	Pitch up / down one scale degree	OSARA higher / lower note in chord
Enter	Toggle note at cursor cell	Edit: Event properties
Alt+G	Toggle grid mode on/off	—
Alt+H	Toggle hold mode	—
Alt+A	Repeat current cell (speak + sound)	—
Alt+S	Set root and scale	—
1–9	Grid size — REAPER's own grid actions	same

Alt+Shift+G opens grid mode; it does not close it. Use Alt+G inside the editor to toggle back off.

How it integrates

• Grid size is REAPER's grid. Read via MIDI_GetGrid(), so whatever you already have bound to the MIDI editor's grid actions (by default 1 = 1/1, 2 = 1/2, 4 = 1/4, 6 = 1/16, 8 = 1/8, 3 = 1/32) drives this too. Nothing new to learn.
• The cursor is REAPER's cursor. Time is the native edit cursor; pitch is the MIDI editor's active_note_row. No private cursor state exists, so grid mode and OSARA cannot drift out of sync — you can switch between them mid-phrase.
• Turning grid mode off restores everything. Each bound key forwards to what it did before, so nothing is permanently taken away.

What gets spoken

• Left / right — cell position and everything sounding in it: "3.2.00, C5, E5", and those notes are sounded together.
• Up / down — the note name, plus "on" if this cell already holds that pitch: "E5, on".
• Enter — "E5 on, added" or "E5 off, removed".

Hold mode

With hold off, toggling adjacent cells at the same pitch gives separate repeated notes.

With hold on, a new note touching an existing note of the same pitch joins it into one sustained note. Toggling a cell off in the middle of a sustained run splits it in two; at either end, it shortens it. So you can draw a long note by arrowing right and pressing Enter across several cells.

Scales

Alt+S prompts for a root (C, F#, Bb…) and a scale number. Up and down then move by scale degree, which is what makes entry fast — you cannot land on a wrong note by accident. Pick chromatic for plain semitone movement.

If the cursor sits on a note outside the current scale, up/down move to the nearest scale tone in that direction rather than getting stuck.

Architecture notes

The action scripts never call reaper.defer. This matters. If a script is still alive when you press its key again, REAPER interrupts you with a "script is already running — terminate or launch new instance?" prompt, which makes fast key repeat impossible and, if you answer "terminate" and tick remember, permanently costs you every second keypress.

So preview note timing lives in MidiGrid_Daemon.lua, a single background loop that auto-starts on first use and relaunches itself if it ever dies. Action scripts post a request to transient ExtState and exit within a millisecond. A new request cuts the previous note, so fast arrowing retriggers cleanly. The daemon releases everything on atexit, so notes cannot hang.

Preview requests use non-persisted ExtState — persisting them would write to reaper.ini on every keypress.

Tunables

In ExtState section midigrid:

Key	Default	Meaning
vel	96	Velocity of inserted notes
chan	0	MIDI channel (0-based)
previewdur	0.4	Preview note length, seconds

Tests

test_lib.lua covers the pure logic — scale stepping, note naming, grid labels — against a stubbed reaper table, so it runs outside REAPER:

lua test_lib.lua

Everything touching MIDI data or the REAPER API is only exercised in REAPER itself.

Limitations

• Preview uses StuffMIDIMessage, which plays through the track's instrument via the virtual-keyboard input, so the track must be armed / monitored — exactly as with REAPER's own MIDI preview.
• The grid aligns to the project timeline (bar lines), not the item start. For an item starting off-grid, the first cell will be partial.
• Note octave naming follows the midioctoffs preference; with the default, note 60 reads as C5.