[pulseaudio-discuss] Avoiding 2ch upmixing to all speakers

Dom H speedsix.lists at googlemail.com
Sat Nov 13 05:16:43 PST 2010

I'm currently giving mplayer's 'pan' audio filter a go, this lets you
decide how each input channel is mixed into the relevant output
channel. As an example, for the centre channel I can specify that 0.5
goes into each front speaker (actually around .65 to get a matching
level all across the front 3) Same goes for the extra rear channels of
8ch tracks such as Dolby EX/TrueHD etc, so for the extra right rear
surround I put .7 into my actual right rear and .3 into the rear left
speaker (again maybe a bit more like .75/.45 as they're too low) For
simplicities sake, pulse is left set to 5.1, it just doesn't receive
anything on the centre channel (which has no speaker attached to it)

Pulse does seem to handle mixing of the extra surround channels in an
8ch mix into 6 but they are VERY quiet and seem to be mixed between
the front and the rear of that side and not offset somewhere between
the 2 rears.

I would prefer to use Pulse for this as I think it's the right place
for it to be done but the inability to adjust the volume kinda kills
it. Well, maybe the volume doesn't need to be configurable, maybe they
just need more output, as in, for a missing centre putting more than
.5 into each front.

I still leave pulse doing the LFE remixing (for music playback) which
works well (still works with a discrete LFE track which is good),
problem is, I can't have JUST lfe mixing enabled without having
upmixing. Setting enable-mixing = no and enable-lfe-mixing = yes
doesn't work. It would be nice if upmixing/downmixing/LFEmixing were
configurable separately. I'm not your average user but imo upmixing
2ch into all speakers is quite an undesirable default. I think
downmixing/LFEmixing should be enabled 'permanently' separately in the
config with upmixing being a clickable option into the volume applet.
Most AV decoders work this way, you have to actually enable upmixing
by switching to a particular mode, downmixing/bass routing is
configured in the setup and always one (you'd set it once and leave

Can pulse be configured for speaker delays aswell? i.e accepting a
distance measurement in metres to set an audio delay in ms for each


On 8 November 2010 20:58, Colin Guthrie <gmane at colin.guthr.ie> wrote:
> 'Twas brillig, and Tanu Kaskinen at 08/11/10 17:47 did gyre and gimble:
>> On Thu, 2010-11-04 at 22:47 +0000, Dom H wrote:
>>> I have a 4.1 system and pulse does a good job of mixing the missing
>>> centre into the fronts for 5.1 audio tracks, I'm recently switched
>>> from a digital out system with my external receiver doing all the
>>> decoding and mixing, to my HTPC doing the job and outputting analogue
>>> to my amp. I'm trying to get pulse to mimic the exact behaviour of my
>>> external decoder, have a few questions though;
>>> 1. Can I stop 2ch audio being mixed to all 4 speakers but retain the
>>> centre mixing into the mains for 5.1 tracks?
>> I don't think so.
> I think one way to get half-way towards this solution would be to use a
> module-remap-sink with a 2 channel setup and the remix=no argument. When
> you want to play 2ch sounds, you will have to explicitly select the 2ch
> virtual device which may not be that convenient.
>>> Have the pulse devs considered replicating how most hardware decoders
>>> handling speaker configuration? As an example, on my Denon receiver,
>>> each speaker can be configured as Large, Small or None. Large speakers
>>> receive regular full range output, small speakers have their low
>>> frequency mixed to the subwoofer output and output sent to a 'None'
>>> speaker is mixed elsewhere (eg centre into fronts) Seems like quite an
>>> elegant solution, would certainly solve all the issues I'm seeing
>>> listed above.
>> I haven't heard that anyone is planning to improve the remixing code.
>> Patches would surely be accepted, though, so it's only a question of who
>> has the time and motivation to do the work.
>> For the issue number one, adding a configuration option for stereo
>> duplication shouldn't be very hard. Any takers?
> I think in the past we discussed how to configure mixing in this way but
> I can't remember what we came up with. I think the general options were
> relating to how mono and stereo sounds were upmixed but further than
> that too much configuration was kinda thought to be unnecessary
> (generally speaking - someone will always find a need of course!)
> Col
> --
> Colin Guthrie
> gmane(at)colin.guthr.ie
> http://colin.guthr.ie/
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