Nyxmix

NyxMix

The open-source alternative to Adobe Audition, built for people and AI agents together.

Multitrack editing, mixing, restoration, spectral repair, loudness mastering and podcast production in your browser. Free, MIT-licensed, no subscription and no account. Everything you can do in the UI, an agent can do through MCP or REST, and you watch it happen live, see who did what, and can undo any of it.

Checked feature by feature against Audition's official reference: of 65 Audition

features, 50 have an equivalent, 14 go further, 1 is partial, none are missing,

and every row is backed by an automated test (full comparison).

Audio output is verified against EBU R128 / ITU-R BS.1770 (48/48 conformance tests).

npx nyxmix   # then open http://127.0.0.1:3950

Screenshots

The demo session was made by an agent with examples/agent-demo.mjs, using nothing but MCP.

Run it

npx nyxmix                               # http://127.0.0.1:3950, sessions in ~/.nyxmix

npx nyxmix --token secret # require "Authorization: Bearer secret" (the UI asks once) npx nyxmix --port 4000 --data ./sessions

Requirements: Node 22+ and ffmpeg 6+ on your PATH (with rubberband, libmp3lame, libopus, which the usual ffmpeg builds have).

From a checkout:

npm install

npm start # same server, data in ./data npm test # integration tests (they boot their own servers) node examples/agent-demo.mjs # an agent producing a podcast episode over MCP

Optional extras

Everything below is optional; NyxMix works without it and tells you clearly when a feature needs one. Python features use a .venv next to the package if there is one, otherwise python3 on your PATH.

Settings

The older KLANG_* names still work.

Sessions as files (.nyxmix)

Save .nyxmix (top bar) downloads a whole session as one file: lossless audio, arrangement, effects, automation, markers, versions, undo history, transcripts, noise prints, reference video and the custom plugins it uses. Open a .nyxmix archive on the start page restores it on any NyxMix server; plugins it brings along are installed after the same checks as a normal install (only where plugins are enabled, never overwriting a different plugin with the same id).

Connect an agent

• MCP (Streamable HTTP): claude mcp add --transport http nyxmix http://127.0.0.1:3950/mcp (with a token: --header "Authorization: Bearer secret")
• REST: /openapi.json, plain-language guide at /llms.txt
• Live events: ws://…/ws?project=
• Send X-Actor: agent: ; the UI labels edits with it.
• Agent skill: SKILL.md

How it is built

• One audio graph, two runtimes. public/js/engine/graph.js builds the mix in the browser's AudioContext for playback and in the server's OfflineAudioContext (node-web-audio-api) for export and analysis. Custom DSP (limiter, gate, de-esser, saturation, BS.1770 loudness meter) lives in engine/dsp-worklet.js and runs as an AudioWorklet in both. What you hear is what you export.
• Every edit is an operation (server/ops.js): JSON-schema validated, applied atomically in batches (later ops can reference earlier results with "$0.trackId"), undoable, logged with its author, broadcast over WebSocket. The UI uses exactly the same calls as agents.
• Lossless storage. Imports become 32-bit float WAV at the session rate. The browser gets a 24-bit FLAC copy (same sound, ~10× smaller). Rendering and destructive processing run on the server in float.
• Feature modules in server/features/*.js register their own REST routes and MCP tools: auto-ducking, proposals and versions, transcription and text-based editing, spectral editing and noise-print reduction.

What it does

Editing — multitrack timeline; move, trim, split, ripple-delete ranges, insert silence, copy/paste, duplicate; snapping; automatic crossfades on overlap; fade curves (linear, equal power, S-curve, exponential); clip gain; markers and range markers; sample-level zoom; undo/redo; named versions.

Mixing — per-track effect chains (parametric EQ with draggable bands, compressor, limiter, gate, de-esser, saturation, echo, reverb, gain) and presets; buses with output routing and pre/post-fader sends; volume and pan automation; auto-ducking under speech; mixer view; live peak/RMS meters and an EBU R128 loudness meter.

Restoration — neural voice denoise (RNNoise), FFT noise reduction, noise-print reduction, hum removal, de-click, de-ess, gate, speech leveler, loudness match and normalize, silence shortening, tempo and pitch (Rubber Band); spectral editor with box selection, attenuate and heal; any process can run on a selected range only, with an A/B preview before applying.

Speech — local transcription with word timestamps; delete words to cut audio; language-aware filler word removal; pause tightening.

Analysis — integrated loudness, loudness range, true peak, sample peak, RMS, clipping, DC, spectral balance, silences, RMS envelope, waveform and spectrogram images (agents can look at them).

Export — WAV/FLAC (16/24/32-bit), MP3, AAC, Opus; loudness normalisation to a target; markers as chapters; stems per track; bounce to a new file.

Agents — MCP server with ~70 tools, REST + OpenAPI, live sync, author on every edit, proposals the person previews and accepts or rejects, versions to return to.

Since the first version — effect-parameter automation and clip volume envelopes; 16 more real-time effects (31 in all: multiband compressor, graphic EQ, multimode and auto filters, expander, transient shaper, distortion, bit crusher, ping-pong delay, pitch shifter, doubler, vocal enhancer, exciter, ring modulator, polarity/DC); true-peak limiter; plugins (AudioWorklet modules, test-rendered before install, off unless NYXMIX_PLUGINS=1); 5.1 surround with a surround panner and 6-channel export; video track with synced picture, filmstrip, frame grabs and scene-change detection; spectral lasso, brush, spot heal and pitch display; automatic pitch correction (WORLD vocoder); de-clipper; clip stretch to an exact length; punch-in recording with monitoring and measured latency compensation; delivery checks (podcast, EBU R128, ATSC, streaming, ACX); export tags, chapters, stems and one file per range marker; session archives; music remix to a target length (beat-matched jumps, editable as clips); manual pitch curves drawn on the spectral pitch display; Generate menu (speech from text, tones, noise, silence); undo history you can jump through; remappable shortcuts; goniometer and phase correlation; user presets; live spectrum analyzer; touch editing; parallel rendering on all cores in crash-isolated processes.

NyxMix vs. Adobe Audition

Output quality is measured against EBU Tech 3341/3342, ITU-R BS.1770-4 true peak and bit-exact null tests in docs/conformance.md (48/48 pass).

The full, test-backed checklist against every effect and feature in Audition's official reference is in docs/audition-comparison.md. Summary:

Where NyxMix goes further: an open API and MCP so agents can edit; live shared sessions with authorship; proposals to review agent changes before they land; transcript-based editing and filler removal; chapter export; it runs in a browser with nothing installed.

Where Audition is still ahead: it loads Windows/macOS VST and AU binaries and runs them live on tracks — no browser can load native plugins; NyxMix hosts 275 native plugins — 110 VST3 and 165 LV2 (LSP, ZAM, Dragonfly, DISTRHO, Calf, x42, MDA) on the server with A/B preview, plus AudioWorklet and Faust plugins (POST /api/plugins/faust compiles Faus