[pulseaudio-discuss] Splitting a 7.1 device into virtual 5.1 + 2.0 devices?

[紅 蒼穹]

Sorry for the late reply, had a busy week.

> The easy way is to use hdajackretask your grey line out as internal 
> speaker, there will be headphone, 5.1 line out jacks and stereo speaker 
I tried that (removing the remap config), but for some reason the only thing pavucontrol now sees is a single audio device that is able to playback at most 5.1 channels. I can't re-route sound to anything else in pavucontrol and the stereo speaker output is silent. I tried both internal speaker and internal speaker (back)

> So the setup is exactly as instructed in the Arch wiki? Two things seem 
> to be wrong in the instructions (I don't know how that could be - did 
> the author not test what he or she wrote to the wiki?): the "remix" 
> option should be "no" in both cases. Otherwise anything played to the 
> stereo sink will be upmixed to all channels of the 7.1 sink. 
But it does work, I'm guessing the author didn't figure out how to improve it. The remix option in this context is a bit misleading, I think. I assumed it meant the sound landing in this sink will be down-/upmixed if set to yes, like the global option.

This certainly explains why the sound is present in front channels of both sinks even though a remapped sink is selected.

>> The second thing is that if the stereo and 5.1 sinks are not supposed 
>> to use overlapping channels, then the channel maps are wrong, because 
>> both sinks use the front-left and front-right channels of the master 
>> sink. The stereo sink should have "side-left,side-right" in the 
>> "master_channel_map" parameter. 
I guess that's another wrong assumption, namely that setting it up like that would mean playing 7.1 content via the ALC889 device would result in side channels playing as front channels on the 2.0 sink...

After applying these two fixes, it now works almost as expected (see below), thank you!

>> - for the Stereo sink, I want the LFE to be mixed into the stereo 
>> channels when downmixing, but left untouched for stereo content (just 
>> like it did with PA6.0). Same for rear and center channels. 
> 
> This does not require any changes to anything. As long as remixing is 
> enabled in daemon.conf (like it is by default), playback streams with 
> LFE will be downmixed to have LFE in the left and right channels, and 
> if the playback stream doesn't have an LFE channel, then there's 
> nothing to do (leaving LFE "untouched for stereo content" doesn't make 
> sense to me, because there's nothing to leave untouched). 

That's not what seems to be happening here, though.

When I have lfe remixing = yes (default):
- LFE is mixed to stereo output when downmixing from 5.1
- there are no low frequencies present at all in 5.1 output when playing a stereo track.

When I have lfe remixing = no:
- LFE is mixed to stereo output when downmixing from 5.1
- LFE (or rather, bass) is present in 5.1 output when playing stereo

So to me, it seems the behavior is exactly inverse to what the description of the option says.

Btw, the current setup triggers that bug I reported [1] in a slightly different way: connecting the headphones switches the device to 2.0 mode, unplugging even without restarting leaves the device in 2.0 mode. This mutes the remapped stereo output.

Regards,
Soukyuu

[1] https://bugs.freedesktop.org/show_bug.cgi?id=94716