Show HN: DJ Mix realtime local AI music with a controller; Magenta, Stable Audio

A developer released Slipmate, an open-source DJ instrument that runs two real-time AI music models locally on Apple Silicon Macs, controlled by text prompts and mixed like vinyl with support for Pioneer DDJ-FLX4 hardware. The tool uses Magenta RealTime 2 for live decks and Stable Audio 3 for generated pads and tracks, requiring ~13 GB of disk space for model weights.

Your generative DJ mate — a DJ instrument for real-time AI music. Two locally-running model decks, steered by text prompts and mixed like vinyl: three-band EQ, one-knob Color FX, a crossfader, headphone cue, and full Pioneer DDJ-FLX4 control. The live decks run on Magenta RealTime 2 https://github.com/magenta/magenta-realtime ; generated pads and finished tracks come from Stable Audio 3. See docs/ROADMAP.md /brxs/slipmate/blob/main/docs/ROADMAP.md for how it got here and for the architecture decisions. /brxs/slipmate/blob/main/docs/adr docs/adr/ - Apple Silicon Mac MLX backend uv https://docs.astral.sh/uv/ - ~13 GB disk for model weights downloaded on first setup: Magenta ~4.5 GB for both deck models, Stable Audio 3 ~8 GB including the medium track model - A Chromium-based browser the app leans on Web Audio worklets and Web MIDI; it is developed and verified against Chrome - Optional: a Pioneer DDJ-FLX4 for hardware control and its headphone jack All common tasks live in the justfile /brxs/slipmate/blob/main/justfile — run just to list them. just setup backend deps, all model weights ~13 GB , frontend deps + build Magenta models land in ~/Documents/Magenta/magenta-rt-v2 override with MAGENTA HOME : both deck models, the default mrt2 small and the heavier, higher-quality mrt2 base , selectable per deck in the UI — the app warns when the combined selection looks tight for your RAM. Stable Audio 3 — generated pads and tracks — is cloned to ~/Repos/stable-audio-3 override with SA3 MLX HOME ; an existing checkout is reused and its weights are pre-warmed so no request ever pays for a download; just setup-sa3 re-runs that half alone. just run Then open http://127.0.0.1:8000 http://127.0.0.1:8000 — add style targets to a deck's pad, hit play, blend targets by dragging the cursor or the dots themselves, to cluster them , and ride the crossfader between decks. Mixer — per-deck volume and Hi/Mid/Low EQ, crossfader, and Record , which captures the master bus to a downloadable WAV. The health row shows the stream buffer, underrun count, and generation speed. Color FX — one knob per deck over a chosen effect: Filter bipolar LPF/HPF , Dub Echo, Space, Crush, Noise, Sweep. The knob's centre/zero is a bit-exact bypass ADR-0008 /brxs/slipmate/blob/main/docs/adr/0008-color-fx-as-one-knob-curves-at-a-pre-fader-insert.md . Freeze loops — capture the last bars of a deck into one of four loop slots and hold the moment on air while you re-steer the model underneath; loops are session-only by design ADR-0009 /brxs/slipmate/blob/main/docs/adr/0009-freeze-pads-loop-played-audio-at-the-channel-head.md . Beat detection — each deck shows its detected BPM behind an honesty gate a dash rather than a wrong number ; with a confident tempo the Dub Echo syncs to the beat and freeze captures quantise to whole beats ADR-0010 /brxs/slipmate/blob/main/docs/adr/0010-beat-detection-on-the-output-behind-an-honesty-gate.md . Deck-to-deck style sampling — one press puts "the sound of the other deck, right now" on a deck's style pad as a blendable target; sampled targets are session-only by design ADR-0011 /brxs/slipmate/blob/main/docs/adr/0011-deck-to-deck-style-sampling-via-audio-embeddings.md . Crates — save a deck's pad + Color FX as a named preset, browse the crate from the FLX4's rotary, and load onto either deck mid-set; export/import as JSON for backup and sharing. Master housekeeping — a limiter on the master the meter, the recording, and the phones all hear the limited signal; its gain reduction shows in the mixer and per-channel auto-gain Trim that levels decks of different loudness, with a manual override. Headphone cue — hit a channel's Cue , ride the Cue mix knob between cue and master, and pick a Phones out : any output device the browser can reach, or the FLX4's own headphone jack, which is fed by the backend over USB ADR-0007 /brxs/slipmate/blob/main/docs/adr/0007-flx4-phones-jack-via-a-backend-cue-sink.md . Settings pad arrangements, volumes, crossfade persist across reloads. Shortcuts: A / B focus a deck's style-target input, X focuses the crossfader. For frontend development: just dev-backend in one terminal, just dev-frontend in another the Vite dev server proxies /ws to the backend . Plug in the FLX4 and click Connect MIDI Chrome asks for MIDI with SysEx; plain MIDI works too, minus position sync . Mapped controls: - Play/pause, channel faders, three-band EQ, crossfader - Channel CUE buttons headphone cue and the transport CUE button deck prep: prime a stopped deck off-air, stop a playing one SMART CFX knob — Color FX amount; hold SHIFT to sweep the style pad instead PAD FX pad bank — select the deck's effect re-press toggles it off ; HOT CUE pads pick style targets; SAMPLER pads freeze loops SHIFT + pad clears a slot HEADPHONES MIX knob — cue mix Browse rotary + LOAD buttons — highlight a crate preset, load it onto deck 1 or 2 Knob and fader positions sync from the hardware on connect, and the LEDs mirror app state. The measured byte map lives in docs/midi-ddj-flx4.md /brxs/slipmate/blob/main/docs/midi-ddj-flx4.md . just test — backend pytest + frontend vitest just lint — format check, ruff, eslint, tsc just check — both of the above; what a PR must pass just verify-stream / just verify-ui — e2e against a running server UI e2e needs Playwright Chromium once: npx playwright install chromium in frontend/ just verify-worklets — the audio-worklet module graph loads in real Chromium self-contained; jsdom executes none of the worklet code - Hardware behaviour is verified by a human against the checklists in docs/ m7- , m9-m10- , m12-hardware-checklist.md