Rythmbox

A cross-platform desktop MIDI file player and SoundFont (.sf2) instrument player built with .NET and Avalonia UI. The UI is styled after hardware drum-machine workstations like the Boss DR-880: a "DrumStage" layout with a live clock, a big now-playing box, a General MIDI percussion pad grid, and a MIDI loop browser.

This is Phase 1 of the project: a solid player. A DR-880-style step sequencer / rhythm workstation (patterns, songs, kits, effects) is planned as a later phase — see Roadmap below.

Features

• Header: live clock, an AUDIO status badge, a one-click SoundFont loader, and the current loop's tempo readout.
• Now Playing: loop position in the browser (e.g. 01/03), PLAYING/STOPPED status, loop name, big BPM readout, and a playback progress bar, with next/previous loop buttons.
• Percussion pad grid: 19 pads mapped to the standard General MIDI percussion note numbers (Kick, Snare, hats, cymbals, toms, congas, cowbell, tambourine, etc.) — works with any GM-compatible SoundFont. Click a pad (or press 1-8 on the keyboard) to trigger it live. Pads actually used by the currently loaded loop are highlighted with a red border.
• MIDI Loop Browser: point it at a folder of .mid/.midi files; each loop is listed with its hit count, duration, and detected BPM. Selecting a loop loads and plays it immediately.
• Transport: a big STOP/PLAY button, SUB (loop toggle), MIXER (opens the mixer overlay), RESCAN, QUIT, and a MIDI-input connect button.
• Mixer overlay (via the MIXER button): SoundFont preset browser with search and an on-screen piano keyboard for auditioning melodic instruments, live MIDI input device selection, a per-channel mixer (mute/solo/volume) for the loaded loop, and the master strip (master volume, RMS/Peak level meter, output device selection).
• Connect a physical MIDI keyboard (cross-platform, via PortMidi) and play it live through the loaded SoundFont.

Keyboard shortcuts

Key	Action
Space	Play / pause the current loop
1-8	Trigger percussion pads 1-8
Esc	Quit

The reference DrumStage layout also has section (A/B/C/D), intro/ending (I/E), and "full" (`) shortcuts. Those depend on pattern/section data that a plain Standard MIDI File doesn't carry, so they aren't implemented in this MIDI-file-based player — they're natural fits for the Phase 2 pattern/song sequencer (see Roadmap).

Tech stack

• .NET 10 / C#
• Avalonia UI 11+ (Fluent dark theme) with the MVVM pattern (CommunityToolkit.Mvvm)
• SoundFlow — cross-platform audio engine (MiniAudio backend) providing SoundFont synthesis, MIDI file sequencing, and MIDI device I/O (via SoundFlow.Midi.PortMidi) in one MIT-licensed package.

Project layout

Rythmbox.slnx
src/
  Rythmbox.Core/     Engine layer (no UI dependency): PlaybackEngine, SoundFontPlayer,
                     MidiFilePlayer, MidiInputService, LoopLibraryService, GmPercussionMap.
  Rythmbox.App/      Avalonia application: Views, ViewModels, styling.

Building and running

Requires the .NET 10 SDK (or newer) with desktop support.

dotnet restore
dotnet build
dotnet run --project src/Rythmbox.App

Getting a SoundFont

SoundFont files (.sf2) are not bundled with this project since most are separately licensed or copyrighted. To try Rythmbox out, download a free General MIDI SoundFont, for example:

• FluidR3_GM.sf2
• GeneralUser GS

Then use Load SoundFont... in the header to open it. Rythmbox automatically arms the standard GM drum kit (bank 128, program 0) on the percussion channel so the pad grid sounds correct right away.

Getting MIDI loops

Use Browse Folder... in the MIDI Loop Browser to point Rythmbox at a folder of .mid/.midi drum loops. Each file is scanned for its note-hit count, duration, and tempo, and listed for one-click playback.

Roadmap

Planned for a later phase, not part of this initial player release:

• DR-880-style step sequencer: 16-step pattern grid per drum voice, with drum kits mapped from the SoundFont's percussion bank.
• Pattern bank and song chaining (arrange patterns into a full song), swing/tempo controls, section (A/B/C/D), intro/ending, and fill buttons.
• Real-time pattern recording and quantization from the already-wired live MIDI input.
• Per-track effects (reverb/chorus/EQ, via SoundFlow's effects components) and a fuller mixer view.
• Saving/loading Rythmbox projects (patterns, songs, mixer state).