Some questions about home cinema sound setups

[The Belgain]

I know pretty much how a computer setup works, since all the decoding is done by the computer itself, but how does this work for standalone DVD players?

For proper 5.1 sound (not using a PC) I need to have a standalone DVD-player outputting to a decoder through digital out, and the decoder decodes (and amplifies) the AC3 signal and sends an analog signal to each of the six speakers right?

So does this mean that the DVD player doesn't have an AC3 decoder? This can't be right because otherwise what does it output to the TV when connected straight to the TV through SCART (without a surround setup)? Surely the TV doesn't have a built in AC3 decoder since loads of old TVs have been around since before DVDs came out. But if the DVD player has an AC3 decoder, then why can't it just output analog signals 6 speakers and save you the price of an extra decoder? I'm confused.

At home at the moment, I have a TV which has Dolby Prologic (ie 4 channel) sound. Does the TV downmix a 5.1 signal it gets from the DVD player? Or does it just get a stereo signal from the DVD player?

The DVD player itself has one digital out, and a left-right (NOT surround) audio output.

An explanation of how this all works would be appreciated, or else a link to a site which explains it.



Also, for computer surround, if a soundcard is outputting through SP/DIF, does it have to be outputting to something with a built in decoder? Is the sound quality of SP/DIF much better than analogue or is it more of a marketing gimmick?

[TRILIGHT]

I can't comment on SCART because I don't know what it is. As for your main question, many DVD players do NOT have a Dolby Digital decoder in them. For a while, some players were being offered with one built in which would output the 6 seperate channels into an amp. They, of course, were more expensive due to the extra electronics. Most of the players I've seen recently however, do not have a Dolby Digital decoder in them. When you output the digital audio, all you are outputting is the digital audio stream. The data is read at the receiver and the receiver's decoder determines what to do with it.

As for SPDIF, it stands for Sony/Philips Digital Interface Format. It is simply digital out. It is and is not a "marketing" thing like you mentioned. It IS digital audio and is better than analog. If your card does not have a decoder and provide for seperate channel outputs then you will need a decoder to send it to. If you are using the SPDIF output, you will need an external decoder. As I mentioned before, all this digital out does is send the data stream out. Something receiving this stream must determine what to do with it.

[The Belgain]

Thanks for the reply, but what I still don't understand is that if most standalone DVD players don't have a built in AC3 decoder, then how can they output sound to a TV (ie something without a decoder)? Surely the DVD player must be able to decode the digital information on the DVD to an analogue signal which it sends to the TV?

[TRILIGHT]

All it does is downmix to 2 channel stereo for output via the analog L and R connections. It does not really "decode", per se, the full Dolby Digital data stream.

[Kb_cruncher]

if your dvd player says "dolby digital" and/or "dts" on the front and has six jacks and/or a "optical"jack then it will decode the ac3 stream.if it does not it won't.

hope this helps.

[TRILIGHT]

Having the optical out jack does not necessarily mean there is a decoder built into the unit. Most all DVD players have this. As you said though, if there is a multitude of jacks back there for outputting the 6 channels (trust me, you'll know! hehe), then you definitely have a DD decoder built into the unit and it will decode this stream for output to your main system.

[arttext]

1. A scart (or euroscart) is a plug which transfers all the signals (stereo audio, composite video and/or S-video, and a siganel for the tv set that there is something going on in the player) and also makes the tv set aware of the fact that a video/dvd starts playing and thus automatically starts on any channel showing this video/dvd.
But beware, thare are different scart plugs on the market, with not all the comnnections wired.
2. A stand alone player can either:
1. Have 6 audio channels out (this means either that it has an amplifier on on board or that you have to use 6 amplifiers LOL, or a six channel (incl. subwoofer) amplifier.
2. An optical or ditigal sound outlet. That means that you need an amplifier with a AC3(dolby 5.1) decoder on board.
3.A combination of any above.