LoopMidi

LoopMidi is a Qt/QML MIDI loop sequencer. It records up to four 16-step MIDI tracks from any MIDI keyboard (e.g. Arturia MiniLab 3) and plays them back together as a continuous loop through a virtual MIDI port that any DAW or synthesizer (e.g. Surge-XT) can subscribe to.

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Features

Feature	Details
4-track recorder	Pick an active record target and edit its 16-step sequence
Layered playback	All tracks play together from the same transport
Record modes	Record every beat in sequence or overdub only the currently playing beat
Virtual MIDI output	Exposes "LoopMidi Output" — connect Surge-XT or any app to it
Passthrough	Notes from your keyboard are forwarded live to the virtual port while playing/idle
Adjustable BPM	40 – 240 BPM slider for playback speed
Project files	Save/load named .loopmidi projects with BPM and all track data
MIDI Learn	Bind transport buttons to any CC knob or pad from each button's right-click menu
Keyboard shortcuts	R record, Space play/stop, C clear, Esc stop all
Beautiful dark UI	Step grid with velocity bars, live note visualizer, animated indicators

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Quick Start (Nix)

# Run directly
nix run github:yourusername/loopmidi

# Or build
nix build github:yourusername/loopmidi
./result/bin/loopmidi

Development shell

nix develop
cmake -B build -DAPP_VERSION=0.3.0
cmake --build build -j$(nproc)
./build/loopmidi

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Setup with Arturia MiniLab 3 + Surge-XT

1. Start LoopMidi — a virtual port named LoopMidi Output appears.
2. Select input port — choose Arturia MiniLab 3 in the left sidebar.
3. Open Surge-XT → MIDI settings → subscribe to LoopMidi Output.
4. Enable Passthrough (on by default) so live notes go straight to Surge-XT.
5. Choose the active track and record mode, press Record (or R), and play notes on the MiniLab.
   Recording stops automatically; playback begins immediately.
6. Surge-XT will receive the looping notes and play them back.

MIDI Learn (MiniLab 3 pads / knobs)

1. Right-click a learnable transport button and choose MIDI Learn.
2. Move a knob or press a pad on the MiniLab 3.
3. The CC or note is captured. That control now triggers the action.

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Architecture

Arturia MiniLab 3
      │  (RtMidi input)
      ▼
  MidiEngine (C++)
      │ passthrough / sequencer
      ▼
  LoopMidi Output  ◄── virtual ALSA MIDI port
      │
      ▼
  Surge-XT (or any DAW)

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Building manually (non-Nix)

Requirements: Qt 6, rtmidi, ALSA (Linux), CMake ≥ 3.20.

cmake -B build -DAPP_VERSION=0.3.0
cmake --build build -j$(nproc)

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License

MIT © 2024 — see LICENSE.