Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <1083943854.722281@news01.eclipse.net.uk>, "Phil"
<_nospam_@_nospam_.com> wrote:
> "MC" <maxcoppin@-don't-send-me-any-spam-btinternet.com> wrote in message
> news:_1Nmc.250$Yd1.112@newsfe1-win...
> > I'm trying to set up my P4C800 to output 5.1 sound to my amplifier via the
> > digital output. I've set up the speakers to be 5.1 and downloaded the
> test
> > file from here
> >
http://www.microsoft.com/windowsXP/windowsmediaplayer/51audio.asp but I
> only
> > get 2 channels. This "soundcard" claims to be 5.1 but does that only
> apply
> > when using analogue connections? I can get 5.1 out through WinDVD, but
> > that's the only way
> >
> >
>
> AFAIK, the S/PDIF connection can only carry one PCM channel, or one
> digitally coded signal. This basically means that although you can get 5.1
> out of digitally encoded files (AC3 aka Dolby Digital), you can only get one
> PCM channel through, which would only be stereo, as you are experiencing.
> The only way to really get round this is to use a soundchip with Realtime
> Dolby Digital Encoding, namely the nForce 2 Soundstorm chipset, but as this
> only for Sckt A mobos, and is the only chip that does this, so you may be a
> little stuck.
> I have an A7N8X-X (the one without soundstorm), and use S/PDIF to my
> decoder, which conveniently has Dolby Surround/Prologic II, so I just set it
> to this and it splits the stereo in to 5.1....not ideal, but it's better
> than just stereo.
>
> HTH
>
> Phil
This is my favorite page for SPDIF. It says (2) 32bit samples are
sent on the cable, and not all the bits are used for the samples
sent to the hardware. I guess that means, without special tricks,
SPDIF is basically stereo. (You can send four channels of sound,
but to do that, I would expect the resolution of the audio samples
would be cut in half?)
http://www.epanorama.net/documents/audio/spdif.html
About half way down on the following page, it mentions that AC3
is a way of coding a multiplicity of channels, into a stereo stream.
On your DVD player application, AFAIK the software is just doing
passthru (transfers AC3 sound samples from the DVD to the SPDIF?).
http://www.dvdsoft.f4w.net/sound.html (about half way down the page)
There is mention of coding software, but I don't see a mechanism
for real time 5.1 software encoding that can be carried immediately
across SPDIF. To do this, would be taking 5.1 to AC3, across SPDIF,
and reconstituted to 5.1 again. Phil mentions the MCP-T DSP block on
the Nforce2 chipset, and that is a hardware assisted way to do it.
Maybe there is some way to do it in software, assuming the latency
caused by the encoding wouldn't be an issue. Keep searching...
You can also get some (useless) info here. Try "AC-3" as a search
term, for example.
http://dolby.custhelp.com/cgi-bin/dolby.cfg/php/enduser/std_alp.php
http://www.dolby.com/lic/technologies
HTH,
Paul
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