I'd like to apply a low-pass filter on the subwoofer channel on my 5.1 sound system under SolydK (a Linux distro based on Debian Testing, PA is installed and configured by default just like under Linux Mint or Ubuntu). I've been trying to achieve this by doing the following.

First, I applied the filter on the LFE channel and created a sink with it:

pacmd load-module module-ladspa-sink sink_name=ladspa_low_pass master=alsa_output.pci-0000_05_02.0.analog-surround-51 plugin=cmt label=lpf control=86

pacmd load-module module-remap-sink sink_name=remapLFE master=ladspa_low_pass channels=1 master_channel_map=lfe channel_map=lfe

Then, I created another sink with the rest of the channels, which I don't want to be filtered:

pacmd load-module module-remap-sink sink_name=remap50 master=alsa_output.pci-0000_05_02.0.analog-surround-51 channels=5 master_channel_map=front-left,center,front-right,rear-left,rear-right channel_map=front-left,center,front-right,rear-left,rear-right

And finally I combined the two sinks into a third one and set it as default:

pacmd load-module module-combine-sink sink_name=combine sink_properties=device.description=myCombine slaves=remap50,remapLFE channel_map=front-left,center,front-right,rear-left,rear-right,lfe channels=6

pacmd set-default-sink combine

The problem is that when I test it with speaker-test -c 6 -t w and sound is supposed to come out from the subwoofer, it is coming from all speakers, and the sample says, ‘rear-centre’.

How can I fix this?

  • It's also possible to do in alsa, use ladspa plugin
    – gena2x
    Jul 16, 2014 at 17:42
  • @gena2x I know, I used to use ALSA directly with Stereo to 5.1 upmixing and LFE low-pass filter, but it would only work when listening to music and it doesn't work at all any more since I switched distro (from Linux Mint KDE).
    – user247824
    Jul 17, 2014 at 10:21

1 Answer 1


Although I haven't been able to figure out the problem with this solution, I have found an alternative one, which seems to be working: using PulseAudio's equalizer, where each channel can be configured separately.

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