Using miditool with GarageBand

GarageBand has no per-track MIDI input selection: it listens to every MIDI source on the system at once. Out of the box that means it hears your raw keyboard and miditool’s output, so every note plays twice, once untransformed. This page fixes that.

The fix

On macOS, miditool can hide the raw keyboard from every other app while it runs. Add hide=true to the input node:

miditool.kdl

input "Roland" hide=true
output virtual="miditool Out"

shuffle-lock seed=42
velocity-curve gamma=0.8

While miditool run is active, the raw keyboard is invisible to GarageBand and everything else; only miditool Out remains. GarageBand hears exactly one stream: the transformed one.

When miditool exits, the keyboard reappears. Nothing about the device or the system is permanently changed.

Start order matters

GarageBand scans MIDI sources at launch and keeps whatever it found. So:

1. Start miditool first: miditool run
2. Then open GarageBand.

If GarageBand was already open, quit and relaunch it once while miditool runs. The same applies after any change to which ports exist.

If a run is killed hard

miditool restores the hidden keyboard on any normal exit, including Ctrl-C. If the process is ever killed outright (a force quit, a power cut), the keyboard can stay hidden. One command recovers it:

miditool unhide

Without an argument it restores every hidden source; pass a name substring to restore one.

When something seems off

miditool doctor

doctor checks the pieces this page depends on: it lists your MIDI ports, warns about sources that look hidden, validates the config, and warns if GarageBand or Logic Pro is already running (and therefore holding the pre-miditool port list). A typical healthy report:

ok    midi backend: 1 input (Roland FP-30 MIDI IN), 1 output (Roland FP-30 MIDI OUT)
ok    config miditool.kdl: parses, 2 top-level effects
ok    no MIDI sources look hidden
warn  GarageBand is running; apps started before miditool keep hearing the raw keyboard until relaunched
ok    Logic Pro is not running

Elsewhere than GarageBand

Hiding is a CoreMIDI feature, so hide=true is macOS only; other platforms ignore it with a note. DAWs with per-track input selection do not need it at all: see Other DAWs.