[pulseaudio-discuss] Weak bass in stereo mode – possibility of virtual 2.1 sound profiles

[Karl Ove Hufthammer]

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