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I'm trying to connect up my Xbox 360 digital audio to my 5.1 speakers via my PC (my LCD has dual input, DVI for the PC, D-SUB for the Xbox).

The motherboard (Abit AB9 QuadGT) has a Realtek ALC888 chipset and I have a 5.1 speaker system connected via 3 x 3.5mm jacks (FR/FL, RR/RL, C/LFE) and I get full 5.1 output from the PC.

I have connected the optical audio cable from the Xbox to the Optical In on the motherboard's backplate.

With the Xbox in Digital Stereo mode I get 2 channel audio from the Xbox, through the PC, to the speakers.

With the Xbox in Dolby Digital 5.1 mode I get no sound at all.

I have the latest Realtek drivers installed in Win 7 32-bit.


  1. Is it possible to use the full 5.1 DD from the Xbox?

  2. If so, am I missing some option(s) in the Realtek setup?

  3. Do I need some other piece of software to do this? (AC3Filter or FFDShow perhaps)

Many thanks

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To answer your questions in order:

  1. Yes, it is. The Xbox 360 supports Dolby Digital 5.1
  2. As long as you have it set to use the digital optical input rather than the sounds on your PC, that's all the setting you need to do
  3. Here is where your problem is. See below:

The problem seems to be that Dolby Digital signals need to be decoded for them to be played. This is no problem for any receivers that support Dolby Digital, because they have built in decoders.

Your PC (or more specifically, your motherboard/sound card), does not have a built in decoder or it would be working. I imagine most 'high end' sound cards have built in decoders.

You do need extra software for this to work.

Looks like realtek claims to have software enabled decoding of Dolby Digital, so you can try that, or,

ffdshow claims to be able to decode 5.1 Dolby Digital and it is FOSS, so you should be good to go with that.

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@th3dude - can you provide a link to the Realtek Decoder info? – Shevek Apr 27 '10 at 10:40
@Shevek - maybe here? these are 'High Definition Codecs' rather than the standard AC97 codecs -… – th3dude Apr 27 '10 at 12:28
that's what I have installed... – Shevek Apr 27 '10 at 12:45
@Shevek - Did you try ffdshow? Its possible that the Realtek software doesn't have DD support. – th3dude Apr 27 '10 at 12:58
going to try it tonight – Shevek Apr 27 '10 at 13:43
up vote 0 down vote accepted

Looks like it's not possible at all:


  • Source outputting an AC3 stream ---> SPDIF input on your computer ---> 5.1 speakers connected to your computer.
  • Source outputting an AC3 stream ---> SPDIF input on your computer ---> AC3 Software Decoder ---> 5.1 speakers connected to your computer.


  • Source outputting a 2 channel PCM stream ---> SPDIF input on your computer ---> L & R speakers connected to your computer.
  • Source outputting a 2 channel PCM stream ---> SPDIF input on your computer ---> Audio signal remixer ---> Audio 5.1 speakers connected to your computer.

lots more info on the link...

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