Re: Weak bass in stereo mode – possibility of virtual 2.1 sound profiles

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Alexander E. Patrakov skreiv 07.10.2018 09:44:

    I don’t understand why this is happening. Shouldn’t
    ‘remixing-use-all-sink-channels = no’ just affect *upmixing* of
    sound,
    and leave 5.1 material alone?


This is a known bug that appears because there are two 5.1 standards: proper 5.1 and 5.1 Side. The video player (I guess you use mpv) says: the extra two channels have to come from the side.

Looks like you’re right. If I run ‘ffprobe’ on my 5.1 test file, it returns:

  Stream #0:1[0x1100]: Audio: dts (DTS-HD MA) ([134][0][0][0] / 0x0086), 48000 Hz, 5.1(side), s32p (24 bit)

So the video file (and mpv) seems to  use the ‘5.1(side)’ standard. (Which is a bit strange, since this is supposed to be a video file to test a normal 5.1 setup, AFAICS.)


But your system does not have speakers there, it has them on the rear. So PulseAudio attempts to remix. In fact, sound both with and without remixing-use-all-sink-channels is wrong.

What’s wrong about the remixing when one uses ‘remixing-use-all-sink-channels = yes’?


Solutions: either upgrade to a 7.1 system or use a different player that doesn't care about Side and Rear. Totem or anything other GStreamer-based should work fine.

I found another solution. In ‘.config/mpv/mpv.conf’, add the following:

  audio-channels=5.1,stereo

Now both 5.1 and stereo material use the correct channel mapping (if I use ‘remixing-use-all-sink-channels = no’ and the 5.1 ouput profile in pavucontrol).

With VLC, I had the same channel mapping problem as in mpv. In the preferences dialogue, there is an ‘Advanced | Audio | Filters | Remap’ setting where I can remap the side audio to the rear speakers. But unfortunately, it doesn’t seem to have any effect (I *have* enabled the ‘remap’ filer in ‘Advanced | Audio | Filters’, and even restarted VLC). But no worries; I prefer mpv anyway, and with the additional config option, everything seems to work fine.

For anyone else who has a similar system (computer connected to a 5.1 receiver / home theatre system using HDMI), here’s all the config file changes I have made to get both stereo and 5.1 sound working perfectly (with PulseAudio 12.2):

In /etc/pulse/daemon.conf, change the default options to
  remixing-use-all-sink-channels = no
  enable-lfe-remixing = yes
  default-sample-channels = 6
  default-channel-map = front-left,front-right,rear-left,rear-right,front-center,lfe

In /etc/pulse/default.pa and /etc/pulse/system.pa, comment out the line (e.g. prefix it with a #)
  load-module module-suspend-on-idle

In .config/mpv/mpv.conf, add
  audio-channels=5.1,stereo


But in reality this should be fixed in PulseAudio code. Maybe I will work on it next week.

That would be great. More stuff *automatically* working correctly is always a good thing! :)


--
Karl Ove Hufthammer

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