New DJ controller software — a free alternative to Rekordbox / Serato.
Status: currently developed and tested on Linux (Ubuntu / PipeWire) with the Pioneer DDJ-FLX4 controller. Cross-platform support (Windows / macOS) and other controllers are next on the roadmap.
- Scans
~/Musicrecursively (mp3, wav, flac, ogg, m4a, …) using ATL for tag metadata - Track table with Artist · Track · BPM · Key · Time columns
- BPM column auto-uplifts as analyses come back from cache / madmom
- SQLite-backed analysis cache at
~/.local/share/sholto/library.db— every track is analysed once and the result survives restarts - 3-tier lookup pipeline: in-memory → SQLite → compute, with automatic write-through
- Best-in-class beat tracking via madmom's RNN + dynamic-Bayesian-network detector (the
madmom-onnxfork — ONNX runtime, no Theano) - Real downbeats drawn as taller / coloured ticks (not "every 4th")
- 3-band frequency split (low / mid / high) per waveform column via biquad filters with 5-tap smoothing
- Stem separation via Demucs (htdemucs — Hybrid Transformer). One-time pass per track produces vocals / drums / bass / other WAVs, cached at
~/.local/share/sholto/stems/<hash>/so re-loads are instant - Live analysis reporter — track rows show an indeterminate progress bar while analysing and a themed ✓ once basic + stems are both done
- Two decks with independent playback, scrubbing, and analysis
- SoundFlow + miniaudio under the hood — routes through PulseAudio / PipeWire on Linux
- Per-track audio cache: load into either deck instantly the second time
- Audio output device selectable at runtime from the Settings menu; chosen sink persists
- Sub-pixel-accurate playhead read straight from the data provider (no drift between 44.1 kHz source and 48 kHz engine)
- Stem-mix playback — once stems are ready, the deck transparently switches to a four-SoundPlayer mix (drums / vocals / bass / other) all sample-locked to the engine clock. Per-stem volume becomes live-mutable
- 3-band Linkwitz–Riley isolator EQ per deck (24 dB/oct crossovers at 250 Hz / 4 kHz). Full-cut all three bands → true silence, like a DJM hardware isolator. Lock-free
BiquadEq3BandSoundModifier, atomic gain updates from MIDI - Magnetic beat-snap — when both decks are playing and their nearest downbeats approach alignment, jog ticks get scaled down by a smoothstep curve and a green glow lights both decks; once you let go, the adjusted deck quantises onto the reference deck's grid
- GPU-baked waveform rendered once at load to a Skia surface; per-frame cost is one textured blit (no per-pixel re-paint)
- Rekordbox-style 3-colour bands that stack low → mid → high outward from the centre line
- Beat-grid markers along the top edge — downbeats highlighted
- Spinning vinyl disc that rotates one revolution per bar at the track's BPM, with a mint-coloured needle peeking out from behind the album-art label
- Outer ring colour transitions green → yellow → orange → red across the track length; flashes when within the last 10 %
- Effective-gain line — a thin mint horizontal line across each waveform showing the combined channel × crossfader volume
- Big track title + artist next to each deck's disc
- BPM rendered both prominently in the deck readout and softly inside the spinning disc label
- Stem activity chips under each disc — coloured parallelogram tags (DRMS / VOX / INST), filled when audible, hollow when muted
- Red mute tint over the whole deck whenever its effective gain is 0 (channel fader down or crossfader fully on the other deck)
- Seven themes selectable from Settings → Theme:
- Tokyo Night (default — navy + neon magenta/cyan)
- Classic (cyan / amber, Rekordbox-style)
- Serato (red / green / blue)
- Smoke (moody warm charcoal + whiskey amber)
- Catppuccin Mocha (soft pastel mauve/peach)
- Glacier (calm Nordic slate-blue)
- Bloodmoon (carbon + crimson + bone — high drama)
Gestures that live across mouse, keyboard, and controller:
- Click the BPM chip on a deck to halve / double the analyser's reading. The chip jumps + flips card-style and lands on the corrected number — fixes the common madmom "doubled it" mistake (e.g. a 87 BPM downtempo coming back as 174). Click again to flip back. Persisted to SQLite per track.
- Hold the controller song-select (browse encoder press) for ~1 s on a highlighted track to force a fresh re-analysis. Bypasses every cache tier and overwrites the stored BPM / beats — rescue path for tracks whose cached analysis is wrong.
- Magnetic beat-snap between decks — when both decks are playing and their nearest downbeats drift toward alignment, jog ticks get scaled down by a smoothstep curve and both waveforms light up with a green stripe at the matching beat. Let go and the adjusted deck quantises onto the reference deck's grid. Same feel as Rekordbox / Serato beat-lock without needing to explicitly arm anything.
- Play / pause on each deck
- Jog wheels — top platter (fast scrub) and side ring (fine seek), with different scrub-rate scaling per surface
- Channel volume faders per deck (14-bit MSB CC, channels 1 / 2)
- Crossfader with equal-power gain curve (14-bit MSB CC, channel 7)
- Top scroll wheel — rotate to step through the track list (signed delta encoder)
- LOAD 1 / LOAD 2 buttons load the highlighted track into the corresponding deck
- HI / MID / LOW EQ pots drive the per-deck isolator (14-bit MSB CC
0x07/0x0B/0x0Fon channels 1 / 2) - Hot-cue pads 1 / 2 / 3 temporarily repurposed as stem mute toggles — drums / vocals / instrumental on each deck (once Demucs analysis has landed)
- Works on Linux via either RtMidi or a built-in
/dev/snd/midi*raw-MIDI fallback (handles cases where RtMidi can't see the device under PipeWire) - Pluggable mappings — drop a new
IControllerMappingintosrc/Sholto.Controller/Mappings/, register it inMappingRegistry.All, and any controller can be supported the same way
- Space play/pause Deck 1; hold Shift for Deck 2
- ← / → seek ±10 s on Deck 1; hold Shift for Deck 2
- Arrow keys intercepted at the window level so the track-list ListBox doesn't eat them
Sholto.Library Track, TrackScanner — domain primitives
Sholto.Analysis WaveformPeaks, BasicAnalysis, beat — pure analysis math, no deps
trackers, AnalysisProvider, MemoryCache
Sholto.Storage SholtoDatabase, AnalysisCodec, — persistence boundary (SQLite)
DatabaseAnalysisCache
Sholto.Audio AudioEngine, DeckPlayer, AudioFileDecoder — playback I/O via SoundFlow / miniaudio
Sholto.Controller MIDI input + Mappings/ — pluggable per-device mappings
Sholto.App Avalonia UI — everything visible
Built on .NET 10, Avalonia 11, SoundFlow (miniaudio under the hood, talks to PulseAudio / PipeWire on Linux). Audio decoding via NAudio + NLayer.
git clone https://github.com/sebastianpatten/Sholto.git
cd Sholto
bash install.sh # one-shot install — .NET 10, ffmpeg, madmom-onnx, demucs, libpulse symlink
dotnet run -c Release --project src/Sholto.Appinstall.sh is idempotent — safe to re-run. It uses sudo apt for system packages and uv for madmom, both standard tools on modern Ubuntu / Mint / Pop! / Debian.
Default to -c Release for everyday use — audio analysis (BPM detection, key detection, stem separation) is CPU-heavy and a Debug build is noticeably slower. Use a Debug build (dotnet run --project src/Sholto.App) only when you actually want the debugger or extra runtime checks.
For iterative development, use dotnet watch so changes auto-rebuild:
dotnet watch --project src/Sholto.App run -c Release --no-hot-reloadThe library scans ~/Music on startup. Click a track in the list to load it into Deck 1; press LOAD 2 on a DDJ-FLX4 to load into Deck 2.
Dual-licensed — see LICENSE:
- Individuals & noncommercial users: free under the PolyForm Noncommercial 1.0.0. Fork it, modify it, gig with it, contribute back — all fine.
- Commercial use (products, hosted services, large-company internal deployment): requires a paid commercial license. Open an issue to arrange.
Small businesses under $1M annual revenue can deploy Sholto internally under the PolyForm terms. The goal is to keep Sholto free for individuals and small shops while asking large companies to contribute back.