Configuring PipeWire Filter Chains to Inject Real-Time Noise Cancellation into System Audio Inputs

נקודות עיקריות

1. Install a noise suppression plugin. LADSPA or LV2 plugins such as rnnoise provide the suppression algorithm.
2. Define the filter chain. A config file declares nodes, links, and plugin parameters in the PipeWire graph.
3. Route the microphone through the chain. Connect the physical input to the filter, then the filter to the application input.
4. Tune plugin parameters. Adjust aggressiveness and VAD thresholds to balance suppression and voice clarity.
5. Persist across sessions. Place the config in /etc/pipewire/pipewire.conf.d so it loads at startup.
6. Verify with a test recording. Record before and after to confirm suppression without artifacts.
7. Monitor CPU usage. Real-time DSP consumes cycles; keep headroom for the rest of the system.
8. Handle multiple microphones. Each input needs its own chain instance or a shared chain with dynamic routing.

Architecture

The microphone feeds a PipeWire filter node that hosts the DSP plugin. The filter output connects to the virtual input that applications read. The graph is managed by WirePlumber, and the plugin runs in the PipeWire process with real-time priority.

Production configuration

# /etc/pipewire/pipewire.conf.d/20-noise-cancel.conf
context.modules = [
  { name = libpipewire-module-filter-chain
    args = {
      node.description = "Noise Cancelled Mic"
      media.name = "Noise Cancelled Mic"
      filter.graph = {
        nodes = [
          { type = ladspa name = rnnoise plugin = "/usr/lib/ladspa/librnnoise_ladspa.so" label = "noise_suppressor" }
        ]
        inputs = [ "rnnoise:in" ]
        outputs = [ "rnnoise:out" ]
      }
      capture.props = { node.target = "alsa_input.usb-mic" }
      playback.props = { media.class = "Audio/Source" }
    }
  }
]

pw-cli list-objects | grep -i 'Noise Cancelled'
pw-link -l | grep -i noise
# record a test
cat /dev/zero | head -c 0; arecord -D pipewire -f S16_LE -r 48000 -c 1 -d 5 /tmp/test.wav
aplay /tmp/test.wav

# adjust in the filter.graph node block
control = {
  "VAD Threshold" = 0.5
  "Noise Reduction" = 0.8
}
# reload
systemctl --user restart pipewire wireplumber

Edge cases from production

• Some plugins introduce latency; measure round-trip delay and compensate in conferencing apps.
• Aggressive suppression clips consonants; reduce the threshold for speakers with soft voices.
• USB microphones with built-in DSP conflict with the software chain; disable hardware processing first.
• Filter chains do not survive a WirePlumber restart unless the config is in the right directory.

שאלות נפוצות