which soundcard would allow me to do this ?

[VJ]

Hello,

I am considering the purchase of a new computer, and wonder if the following is possible. My computer is located relatively close to my TV and hifi. A lot of soundcards currently allow Dolby AC3 decoding (dolby digital) for games and DVD-rom drives.

Which soundcard would allow me to perform such decoding for a tv-signal ? A lot of tv-stations here in Belgium use digital sound, and quite often movies are shown using dolby pro-logic or even dolby digital. (My parents tv has a dolby-prologic decoder, and I definitly know it works for movies being broadcasted.)

Without having to buy such a tv or a home-theater amp (I have a very good analogue amplifier - Onkyo 9711 Intregra), what hardware (and connection-setup) would I need to be able to use my computer as an ac3 decoder (I could then route the front audio to a line in on my Onkyo, the rear audio to an old JVC amp) ? I imagine the soundcard would have to support 4 or 6 speakers (e.g. Turtle Beach), but what about the input ? All I have is an RF signal, and an analogue stereo-signal (TV-output). Can this analogue stereo-signal still be decoded, or would I need some form of RF -> digital setup ?

Thanks !


Jörg

[VJ]

Well, I browsed the dolby website, and found this schema for dolby pro-logic.
<img>http://www.dolby.com/graphics/img/fig02-60.jpg</img>
This makes me think that the stereo-signal coming from the tv can still be decoded. Can anyone confirm ? Now I'm still searching for Dolby Digital (I know I'd then also need to add a center speaker to my setup).

Any thoughts ?


Jörg

[Greebe]

Verstraete J, the diagram you have found is an electronic variation of an old theme. If you connect any pair of relatively cheap speakers negative terminals together and then wire each positive terminal to the hot (+) side of both right and left channel then you have what is called ambience speakers. Ambience speakers only produce the differencial signal portion of the stereo signal. Additionally depending on placement, this can be also used for image enhancement instead of for ambience.

All Dolby did was add a delay (we used BBDelays in the day for this (20+ years ago))and toss in a quasi B-type filter to reduce hiss commonly found in TV broadcasts (not required for use with CD quality music) and a gain control to allow the user how much ambience they prefer (typically <15% of the overall signal).

[az]

Dolby Surround (and Pro-Logic) is basically just enhanced stereo, and is "encoded" into the stereo signal, therefore you only need a stereo signal for it (in fact, this is the only method of broadcasting it, afaik). Dolby Digital (AC3) on the other hand uses 5.1 real channels, and there is no way getting a Dolby Digital signal out of just two channels. I know some TV stations here say they broadcast in Dolby Digital too, but how to decode it (or how they broadcast it, because it's their normal program and you need no set top box for it) is beyond me. So Dolby Surround would be your only option, perhaps with Dolby Digital as an enhancement if you use your PC as a DVD player (you'd need a graphics card with a TV out, of course).

AZ

[VJ]

Thanks for confirming the simplicity of the Dolby surrond (and prologic) setups !

-
Dolby Digital (AC3) on the other hand uses 5.1 real channels, and there is no way getting a Dolby Digital signal out of just two channels. I know some TV stations here say they broadcast in Dolby Digital too, but how to decode it
-

I have browsed the dolby websites, and found some schematics on ac3 (part of a pdf file). Decoding the ac3 signal requires some processing power (5 channels analogue are coded into a 2 channel digital broadcast). I think it should work if I could find a tv-tuner that offers a digital audio output (similar to the output on a dvd-drive). The actual decoding of the signal could then be done by the soundcard. But up to now I had no luck in finding such a tuner on the web (I also searched for e.g. a tv-card with a digital out, but no luck), not even in diy kits.

As you say, dolby pro logic is still an option, but there is quite a difference between pro logic and digital...

Thanks!


Jörg

[VJ]

I think I might have found something. The ATI all in wonder card (combined vga/tv) has an s/pdif connect for digital out (as they mention on their website.

On the French Matrox site, the specs for the Marvel G200 TV tuner upgrade state :
"Sortie audio S/PDIF par connecteur RC pour le son Dolby Digital des titres DVD (nécessite un ampli Dolby Digital et le module Matrox DVD Video)" This is not mentioned on the English matroxsite... Is there an s/pdif on the Rainbow runner G ?

Does anyone has knowledge of stand-alone TV-tuner cards with an S/PDIF connection (I would like to keep a Matroxboards as videocard).

Jörg

[J1NG]

There is indeed a SPDIF connection on these BOB (Break Out Boxes). But as far as I'm aware, they only work with the Hardware DVD Module for the Marvel G200. I could be wrong though.

J1NG

[VJ]

It would seem to me that if it is a true S/PDIF, it should be possible to connect this to a digital input ?

But then again, it could be that the S/PDIF only gives output when dvd's are played through the hardware-module.....

Jörg