Loom

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Playback ​

Loom's CLI and Studio do not include a synthesizer. They send MIDI events to an output port, and another app turns those MIDI events into sound.

Playground is different: it uses a small GM-lite browser preview built on WebAudio samples. That preview is useful for quick browser feedback, but it is not a complete General MIDI sound source. Use MIDI playback or MIDI export when you need accurate playback through your own synth.

The recommended local setup is FluidSynth with a General MIDI SoundFont.

FluidSynth with Nix ​

If you already have a SoundFont installed, start FluidSynth like this:

bash
nix run nixpkgs#fluidsynth -- -a coreaudio -m coremidi ~/Library/Audio/Sounds/Banks/FluidR3_GM.sf2

For debugging, add -v to print incoming MIDI events:

bash
nix run nixpkgs#fluidsynth -- -a coreaudio -m coremidi -v ~/Library/Audio/Sounds/Banks/FluidR3_GM.sf2

nix run nixpkgs#fluidsynth already launches the fluidsynth binary. Do not repeat fluidsynth after --.

FluidSynth with Homebrew ​

Install FluidSynth:

bash
brew install fluid-synth

Then start it with the same Core Audio and Core MIDI drivers:

bash
fluidsynth -a coreaudio -m coremidi ~/Library/Audio/Sounds/Banks/FluidR3_GM.sf2

For debugging:

bash
fluidsynth -a coreaudio -m coremidi -v ~/Library/Audio/Sounds/Banks/FluidR3_GM.sf2

Adjust the SoundFont path if your .sf2 file is somewhere else.

Play from Loom ​

In another terminal, list MIDI output ports:

bash
loom ports

Pick the FluidSynth port index, then play or live-code:

bash
loom play examples/starter/melody-simple.loom --port 0
loom live examples/starter/melody-simple.loom --port 0

If the FluidSynth port is not listed, restart FluidSynth and run loom ports again.

MIDI Monitor ​

If sound does not play, use MIDI Monitor to check whether Loom is sending MIDI events. It is useful for verifying note, channel, control change, and program change messages before debugging the synth or audio output.