# Show HN: DJ Mix realtime local AI music with a controller; Magenta, Stable Audio > Source: > Published: 2026-06-15 11:40:35+00:00 **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` )