Cardioid

A virtual microphone for PipeWire. Cardioid reads one physical mic, runs it through noise reduction, a filter, gate, compressor, de-esser, equalizer and limiter, and offers the result to OBS, Discord and other apps as an input called Cardioid.

It handles the microphone and nothing else. Desktop audio has no route into the chain, and if the mic is unplugged the input stays silent until the mic returns. It never falls back to another source. The name comes from the cardioid pickup pattern, which takes sound from the front of a mic and rejects the rest.

Filters

Stage	Plugin	Preset
Noise reduction	RNNoise	Voice threshold 65 %
Filter	LSP Filter	High-pass at 90 Hz, 24 dB per octave
Gate	LSP Gate	Opens at -50 dB, reduces by 40 dB
Compressor	LSP Compressor	3.2:1 from -18 dB, 5 dB makeup
De-esser	Calf Deesser	-22 dB at 4.8 kHz
Equalizer	LSP Parametric Equalizer x8	About -2 dB near 270 Hz, up to +3 dB at 3 to 5 kHz
Limiter	LSP Limiter	-3 dB, lifted back to 0 dB

The preset was tuned by ear on a HyperX DuoCast. Other mics will probably need different input gain and gate settings.

Requirements

• PipeWire with WirePlumber, including the pw-* tools and pactl
• lsp-plugins-lv2, calf and noise-suppression-for-voice
• Rust 1.95 or newer, only when building from source
• A desktop with a StatusNotifierItem tray. KDE Plasma has one built in, GNOME needs the AppIndicator extension.

On Arch-based distros:

sudo pacman -S lsp-plugins-lv2 calf noise-suppression-for-voice rust

Cardioid is developed on CachyOS with KDE Plasma on Wayland and PipeWire 1.6, and hasn't been tested anywhere else. Other distros need the same plugins under their own package names. The installer only checks for them on pacman systems.

Install

Download cardioid-<version>-x86_64-unknown-linux-gnu.tar.gz from the releases page, then:

tar -xzf cardioid-*-x86_64-unknown-linux-gnu.tar.gz
cd cardioid-*-x86_64-unknown-linux-gnu
./install.sh

To build from source instead:

git clone https://github.com/PanzerPeter/cardioid
cd cardioid
./install.sh

The script installs Cardioid into ~/.local/bin, building it first when run from a clone, adds it to the app menu and starts it at login. ./install.sh --uninstall removes all of that and keeps your settings.

Use

Pick Cardioid as the input in OBS, Discord or any other app, then turn off that app's own noise suppression and automatic gain so they don't work against the filters.

Closing the window leaves the filters running in the tray. Quit from the tray menu stops them. While no app is listening the mic stays closed, and it opens while the Cardioid window is open so the meters can show a level.

Drag or scroll a knob to change it, hold Shift for fine control, and double-click to go back to the preset. Settings are saved to ~/.config/cardioid/settings.json.

Test recording

Record a test captures 10 seconds before and after the filters at the same time, so With filters and Original play back the same words. Playback goes to your default output and never reaches the virtual mic. The takes are stored in $XDG_RUNTIME_DIR/cardioid and deleted when you close the window.

Troubleshooting

Problem	Fix
The app says the mic is sending pure silence	Check the mic's mute switch and gain.
The app says the filters aren't running	Quit from the tray, run cardioid --background in a terminal and read the plugin error it prints.
Cardioid isn't listed in an app	Check that it's running with pactl list short sources, then restart the app.
No tray icon on GNOME	Install the AppIndicator extension.

How it works

PipeWire's filter-chain module hosts the plugins in a separate pipewire -c process, so no audio passes through the Rust code. Its capture stream targets one device with node.dont-fallback and node.linger, which makes WirePlumber wait for that device instead of linking anything else.

The background service owns the tray icon and restarts the filter process if it stops. The window is its own process that sends parameter changes with pw-cli, so closing it frees its memory.

Run the tests with cargo test. cargo test -- --ignored also checks a running service and a connected mic.

License

MIT, see LICENSE. Fira Sans in assets/fonts is under the SIL Open Font License. The audio plugins are separate projects that PipeWire loads at runtime, and Cardioid doesn't include them.