• Install Debian package sox.

  • Load the kernel module snd_aloop to create an ALSA loopback device.

    sudo modprobe snd_aloop

  • Record a noise and generate noise profile using sox.

    sox noise-from-headset.wav -n noiseprof noise-from-headset.prof

  • Use pacmd to get the device name of the newly created loopback device for output, which should be alsa_output.platform-snd_aloop.0.analog-stereo.

    pactl list | grep -E -A2 '(Source|Sink) #' | grep 'Name: ' | grep -v monitor | cut -d" " -f2 | grep output.*aloop

  • Pipe the audio stream from the microphone through sox.

    pacat -r -d echoCancel_source --latency=1msec | sox -v 0.8 -b 16 -c 2 -e signed -t raw -r 48000 - -C 0.5 -b 16 -c 2 -e signed -r 48000 -t raw - noisered /home/jihuan/文档/Documents/computer/linux/experiment/2024-04-03-reduce-noise-from-microphone/noise-from-headset.prof 0.21 | pacat -p -d alsa_output.platform-snd_aloop.0.analog-stereo --latency=1msec

  • Record in Audacity or some other tool using the loopback ALSA input source alsa_input.platform-snd_aloop.0.analog-stereo. This device name can be obtained by running this command:

    pactl list | grep -E -A2 '(Source|Sink) #' | grep 'Name: ' | grep -v monitor | cut -d" " -f2 | grep input.*aloop

N.B. alsa_input.platform-snd_aloop.0.analog-stereo is a virtual device in the loopback sound card, which is to be connected to a recording application. Meanwhile, echoCancel_source is the actual PulseAudio device to receive physical audio stream collected from the microphone. Therefore, the default source of PulseAudio should be set to echoCancel_source, but not alsa_input.platform-snd_aloop.0.analog-stereo.

References