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

Tanu Kaskinen tanuk at iki.fi
Mon Nov 8 09:47:32 PST 2010

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.

> 2. Can I increase the volume of the centre that is being mixed into
> the mains, it's a dB or so too low?

No, there's no such detailed configuration options.

> 3. When LFE mixing is enabled, does it route bass frequencies into the
> subwoofer channel even when there is a discrete LFE track?

I don't think so (I'd need to check the code to be sure, though). One
thing to note is that the remixing code doesn't deal with frequency
bands. The output channels always get the full spectrum from the input

> 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?


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