Cathode

A guitar processor for your computer, in the spirit of the Axe-Fx III. Plug your guitar into an audio interface and build a rig from circuit-modelled amps, cabinets, drives and effects on a grid, with scenes, channels and modifiers for playing live. It runs on your Mac or PC, or on a small Linux computer in your rig that you control from any browser.

Cathode is free and open source (GPL-3.0-or-later).

Status: release candidate. 1.0.0-rc.4 is the fourth release candidate; see the changelog. Presets saved from 1.0 on keep loading in later releases.

What it does

• 88 amp models, each built from its schematic: stage by stage, with the tone stack, power amp, transformer and speaker load, and the amp's own front-panel controls. Plus expert settings (tubes, bias, sag, supply) behind them.
• Neural captures: load NAM (.nam) and AIDA-X models in the Amp NAM block.
• Cabinets: a Cab block that builds the response from 10 speakers, 11 microphones and 7 cabinets, with mic position, distance and angle. Load your own impulse responses (.wav, .cabgrid) too, mix them, trim them, or capture one with a sine sweep.
• 48 block types: drives, delays (including multi-tap, ten-tap and plex delays), reverbs, chorus, flanger, phaser, rotary, tremolo, wah, pitch and harmonisers, synth, vocoder, compressors and gates, EQs, filters, a looper, a tuner, mixers and FX loops.
• A grid like the hardware's: six rows of fourteen cells, parallel paths, mixers and feedback loops.
• Built for playing live:
  • eight scenes per preset, and four channels per block;
  • modifiers driven by LFOs, envelopes, a sequencer or MIDI controllers;
  • a Perform page with big controls;
  • MIDI control and footswitch layouts;
  • a metronome and tap tempo.
• A library:
  • presets with banks and setlists, snapshots and templates;
  • block presets;
  • NAM amps and IR cabs, all in one place.
• Several inputs and outputs: up to six inputs, four stereo outputs with their own EQ, an FX loop, and a DI out for reamping.

Download

Get the latest build from the Releases page.

Package	For	Notes
Cathode-<version>-mac-arm64.dmg	macOS on Apple Silicon	Not notarised yet: on first launch, right-click the app and choose Open.
Cathode-<version>-win-x64.exe	Windows 10 and 11	Not signed yet: SmartScreen asks you to confirm.
Cathode-<version>-linux-x86_64.AppImage	Linux desktops	Make it executable (chmod +x) and run it.
cathode-server-<version>-linux-<x64|arm64>.tar.gz	A small Linux computer in your rig, with no display	See the headless rig.

Each release lists SHA256SUMS to check the downloads against. Every file and SHA256SUMS itself carry a signed build-provenance attestation: gh attestation verify <file> --repo Rikarin/cathode shows it was built by this repository's release workflow (verifying a download).

Where it plays sound today

Platform	Audio and MIDI
macOS	✅ CoreAudio and CoreMIDI
Linux	◐ ALSA (direct, no sound server) and JACK or PipeWire, with ALSA sequencer MIDI, early: tested in containers, not yet on a real interface
Windows	◐ WASAPI, ASIO and WinMM MIDI, early: WASAPI tested on shared-mode output only (exclusive mode and inputs still need a real interface), ASIO only against Steinberg's sample driver

Without a working audio driver, Cathode runs on a silent "null" backend: you can build and edit presets, but you will not hear them.

Getting started

1. Connect your audio interface and open Cathode.
2. Open Settings (⌘, on a Mac, Ctrl+, elsewhere), go to Audio setup, and choose your interface, its sample rate and buffer size. 64 samples at 48 kHz is the target. A loopback test there measures your real latency.
3. Double-click an empty cell on the grid to add a block. An Amp and a Cab between Input and Output make a rig.
4. Select a block to edit it in the drawer below the grid. Right-click a knob to add a modifier or put it on the Perform page.
5. Save with ⌘S. Press ? to see every keyboard shortcut.

Your presets and assets are stored in Cathode's data folder (~/Library/Application Support/Cathode on a Mac).

A headless rig

The cathode-server package runs the engine and the server on a small Linux computer (a Raspberry Pi 5 or a mini PC) with your audio interface, and serves the editor to the network. You play and edit from a phone, a tablet or a laptop's browser, or from the desktop app's remote-server connection.

tar xzf cathode-server-<version>-linux-arm64.tar.gz
cd cathode-server-<version>-linux-arm64
sudo ./install.sh

The installer starts Cathode at every boot and prints the address to open and an access token. See packaging/headless/README.md for choosing the audio interface, updates and logs.

Licence and trademarks

Cathode is free software: you can redistribute it and modify it under the terms of the GNU General Public License, version 3 or (at your option) any later version. See LICENSE. The third-party code built into its native libraries, and the licence each is used under (the Windows ASIO backend uses Steinberg's ASIO SDK under GPLv3), is listed in THIRD-PARTY-NOTICES.md.

Cathode is not affiliated with or endorsed by Fractal Audio Systems. Axe-Fx is their trademark. Amplifier, speaker and microphone names belong to their owners and are used only to say which equipment a model is based on.

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Development

Repository layout

Folder	What's in it
engine/	The C# (.NET 10) engine: the DSP library, the NativeAOT real-time host (cathode-host), the ASP.NET Core server (cathode-server, REST and WebSocket API), the native audio and NAM shims (engine/native), tests and tools. See engine/README.md.
editor/	The Angular editor and the Electron desktop app (an Nx workspace). See editor/README.md.
website/	The project's website: an Angular page prerendered to static HTML. See website/README.md.
packaging/	The headless rig package: build script, installer and systemd services.
docs/	The design: architecture, testing, plan, amp modelling, , , , and the .

The engine runs as two processes: an allocation-free NativeAOT host that owns the audio thread, and a server that holds presets and serves the API, so its garbage collection never touches the audio. Blocks are described once (a descriptor of parameters and pages) and that drives the DSP, the API's validation, the editor's generated controls and the tests.

Build

You need the .NET 10 SDK, Node with pnpm, and CMake with a C and C++20 compiler (on Linux, also libasound2-dev).

cd engine && native/build.sh && dotnet build -c Release

cd editor && pnpm install

Run

The desktop app starts the engine host and the server itself:

cd editor && pnpm exec nx serve desktop

For quick UI work in a browser, run the engine host without a device, the server, and the editor's dev server:

cd engine && dotnet run -c Release --project src/Cathode.Host -- --serve --null-audio --socket /tmp/cathode-host.sock

cd engine && dotnet run -c Release --project src/Cathode.Server -- --Cathode:Engine:SocketPath=/tmp/cathode-host.sock

cd editor && pnpm exec nx serve editor

The server listens on http://127.0.0.1:5180, with OpenAPI at /openapi/v1.json; cathode.http walks through the API. To run the host on a real device as a separate process, see engine/README.md.

Test

cd engine && dotnet test -c Release

cd editor && pnpm exec nx run-many -t test

cd editor && pnpm exec nx e2e desktop

The engine suite covers every block (generated conformance tests, zero allocation on the audio thread), the amp models against circuit simulations of their schematics, golden renders and the API. The desktop end-to-end tests drive the real Electron app with the engine on the null backend.

Release

Push a version tag (v1.2.3) and release.yml builds every package on its own OS and publishes a GitHub release. See docs/10-releases.md.