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Optical SPDIF input and surround sound - HELP

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  #1  
Old 16-12-2007
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Join Date: Dec 2007
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Optical SPDIF input and surround sound - HELP

Hello everyone,

I need some help real bad.

I recently bought a cheap-o 7.1 soundcard for its optical SPDIF input.
I wanted to use the optical in to connect my PS2 through it, and so get surround sound.

I managed to connect through the SPDIF, but I am only getting stereo sound. Of course I checked with a game that has dolby digital output. I have this sneaking suspicion that the signal is not being decoded properly.

Any ideas?

Many thanks

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  #2  
Old 16-12-2007
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Join Date: Feb 2006
Posts: 176
Re: Optical SPDIF input and surround sound - HELP

Though SPDIF has 4 channel mode of operation but it is infact two channels stereo because it is at a reduced resolution
which makes the 4 channel mode useless. In order to carry 5.1 across the coaxial cable you will need Dolby AC3 encoding. So if you have AC3 capable stereo with TOSLink input, maybe you could verify that AC3 is actually on the link from your game at current time. So better click the below URL and download AC3filter tool: http://ac3filter.net/projects/ac3filter
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  #3  
Old 17-12-2007
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Join Date: Dec 2007
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Thank you Paul for your complete reply

At least I understand the situation now.
I will start experimenting and come back with my results.

Michael
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  #4  
Old 18-12-2007
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It seems that the AC3 filter cannot at the moment accept input through SPDIF and decode it.

It is supposed to be a planned feature but not yet implemented.

http://ac3filter.net/forum/viewtopic.php?t=130

Any ideas? Any other possible ways to solve the problem?

thanks
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  #5  
Old 21-12-2007
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Join Date: Sep 2004
Posts: 129
Re: Optical SPDIF input and surround sound - HELP

I think you need something like a high end Creative card that is capable to do decoding. I know one that is KXproject that is said to be capable for the same but it only provides a driver for the EMU10K based cards. Check it here http://kxproject.lugosoft.com/index.php?skip=1
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  #6  
Old 23-12-2007
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Join Date: Dec 2007
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Oh wow Paul.

I'm humbled by the effort you put in for me. I would never have gone that far in my research because I don't understand the subject. It took me quite some time to understand all that you are writing even :)

I think I will look into the KXproject for now, since money is tight and I only want the PS2 to get working with proper sound. And hopefully when all this is done, I will have learnt a few more things as well :)

I am truly grateful Paul, you're a good man.

Michael
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  #7  
Old 24-12-2007
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My Experience with this Issue...

Think I have your answer - I was just actually working on the same problem but w/ Xbox - except that I bought a relatively expensive soundcard w/ SPDIF optical in (bluegears b-Enspirer) and all the Dolby / DTS licenses (DD Live, DTS Connect, DTS Neo-PC, etc).

At first, I was playing w/ surround sound so I was thrilled - but then I was reading more about the card/technologies and began wondering if what I really was getting was true Dolby Digital or just Dolby Digital IIx (which the card natively processes) b/c the big thing abt this CMedia "Oxygen" chipset that the b-Enspirer card houses is Dolby Digital and DTS ENCODING NOT DECODING which is what it should be doing if I were getting true 5.1 Dolby Digital.

After a few hours of research here are my findings (will discuss PS2 shortly):
So apparently Xbox transmits an AC3 (i.e. Dolby Digital signal) via the Nvidia SoundStorm soundcard it houses. I found out from the Dolby gaming website that in order to take advantage of DD, one needs to enable DD upon startup. And so I enable it and like Paul mentioned in an earlier post, I got a bunch of noise. So the sound card doesn't actually decode Dolby Digital but I still got one hell of a sound card for pc gaming / music. :)

So now onto PS2 which I also own - from that same Dolby gaming website (http://www.dolby.com/consumer/games/yourconsole.html), it says that

"Most PlayStation 2 games use Dolby Pro Logic II exclusively because the PlayStation 2 cannot process interactive Dolby Digital during game play. Some games, however, may feature select cinematics in Dolby Digital."

Also from PS2's Wikipedia entry:
* Output: Dolby Digital 5.1 Surround sound, DTS (Full motion video only), later games achieved analog 5.1 surround during gameplay through Dolby Pro Logic II

So this means that you are getting what you should expect to be getting - a stereo signal via the SPDIF cable as PS2 CANNOT process a true AC3 or DTS signal during gameplay. Dolby Pro Logic II is simply a matrix decoder that converts 2 channels to 5.1 channels.

So like me, if you want to get a true Dolby Surround experience from your console, you'll have to invest in a Dolby Digital receiver (all Dolby Pro Logic II receivers also have Dolby Digital) or possibly an X-Fi card as I read that it does native Dolby Digital decoding (though it is done in software and will result in lag).

Hope this helps.
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