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

[Tanu Kaskinen]

On Sun, 2016-03-27 at 14:35 +0200, 紅 蒼穹 wrote:
> Hello,
> 
> I'm using an ALC899 codec with 6x3.5mm jacks and so far, I've been
> using sink-remap [1], which worked fine, 5.1 sound being remixed to
> 2.0 as expected.
> 
> However, there are two problems with this:
> - even though I select the Stereo sink as output in pavucontrol, the
> sound is also playing via my Surround sink
> - the two sinks have their volumes linked.

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.

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.

> Apparently, I could set my card to 5.1 and the grey socket would be
> automatically treated as a 2.0 device, however the behavior is
> completely the same as my earlier setup, including the caveats
> described above
> 
> I would like to split them in separate devices as follows:
> 
> - two sinks visible, Stereo (for the 2.0 amplifier) and Surround (for
> my 5.1 headset with a built-in amplifier), physical 7.1 device hidden
> in pavucontol/KDE's plasma-pa widget

Hiding the 7.1 sink is not currently possible.

> - 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).

> - for the Surround sink, I want the LFE to use the subwoofer, as
> standard PA7.0 behavior.

As long as the 5.1 sink's lfe channel position is the same in both
"channel_map" and "master_channel_map", that's what will happen.

> - selecting one of the sinks should only play sound on that sink, not
> both of them

A playback stream can only play to only one sink anyway. I assume that
your confusion arises from the upmixing that was done between the
stereo sink and the master 7.1 sink due to the "remix=yes" parameter.

-- 
Tanu