[pulseaudio-discuss] Pulseaudio&Surround&

Jon Smirl jonsmirl at gmail.com
Tue Aug 26 11:26:26 PDT 2008

On 8/25/08, Achim Frase <achim.frase at googlemail.com> wrote:
> Am Montag, den 25.08.2008, 16:18 +0200 schrieb tyrchyus:
> > Hi i'm an italian guy. I wrote a guide to set pulseaudio surround with
>  > a52 alsa-plugin.
>  >  I want to know what do you think about and if it is the right way.
>  >
>  > link: http://wiki.ubuntu-it.org/MarcoTacchini/Prove1
>  >
>  > thanks
>  >
>  > tyrchyus
>  >
> Hello Tyrchyus,
>  I can not answer your question but I am a bit curious what you are
>  doing. It looks a bit difficult to me. Don't get me wrong I only want to
>  understand what the reason is for all that.

I was running with a52 for a while and turned it off. It constantly
chews 50% of a core on a Q6600 with music playing.

You set pulse up to run with 6 channels. a52 then takes these 6
channels and AAC compresses them in real time and sends the results
out over SPDIF. If you don't run a52 you only get stereo over the
SPDIF line. This way you get 5.1.

The purpose in doing this is to use a cheap 5.1 Home Theater in a Box
as a PC sound system. In fact they work extremely well as a PC sound
system. I have a $250 Sony system on my machine right now. 1KW sub
came with it.

Now a days most motherboards have SPDIF out. SPDIF is a digital output
so there aren't any quality issues with the motherboard based audio
hardware.  There is no need to buy a fancy audio card, the hard work
happens in the external system.

Internally my Sony system takes this digital output and uses it to
digitally drive a digital PWM Class-D amp. There is no A/D conversion
in the system at all except in the speakers which convert the PWM
pulses to sound. No A/D D/A removes many sources of noise and jitter.

a52 has real potential as a valuable desktop feature but not enough
work is being done with it. It is too hard to configure and it uses
way too much CPU. There are much faster AAC encoders available that
could be used to speed a52 up. I love to be able to enable it with a
simple check box.

>  Is that a hardware specific solution, because I only edit
>  "default-sample-channels = 2" to 6 in /etc/pulse/daemon.conf and also
>  turne up the volume of front, surround, Center, LFE in the gnome Alsa
>  mixer. After that surround sound is working like it should. I hear
>  stereo sound on all 6 channels without problems. I also have no problems
>  with AC3 sound if I watch a movie with totem.
>  In my case I don't need the alsa-plugin.
>  My hardware:
>  product: 82801H (ICH8 Family) HD Audio Controller
>  It would be nice if you could enlighten me.
>  Maybe I don't get the use case right.
>  Regards
> Achim
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Jon Smirl
jonsmirl at gmail.com

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