Need some guidance guys

[ANONANON]

I'm watching an old yamaha HTR-5540 amp on ebay. It has just one optical input which is all i need for my htpc.

My htpc will have either a xonar DX or xonar DG installed. Will i get the full 5.1 sound experience with this setup without any further equipment by using SPDIF cable? Do these cards decode the data or do they just pass it through to the amp for that to decode it?

If SPDIF won't work, will i be able to connect the green, black and orange plugs of the sound card to the 6ch input section of the amp (top left of the picture)

Sorry for the noob questions but it's so confusing to me. Dolby digital live, pro logic II, DTS, THX, PCM

 

[Marsman]

That's very few inputs that AV receiver has. What if you want to add other devices at some point? Console, Sky, etc?

If you are sure only the two SPDIF inputs is all you will ever need, then you won't have a problem connecting to your HTPC via one of the two Xonar cards. If you are not going to use for gaming at all, then a DG/X will suffice.

Any DVD or media file with 5.1 AC3/DD/DTS audio track, should be passed on by the software to the receiver to decode. With DVD's this is easy with pretty much any playback software. With some media files though, it can be a pain, depending on the software player.

That receiver does have 5.1 direct input, so you could if you wanted, use the analogue connections on the card using cables that split the 3.5mm jacks into two RCA/phono connectors.

Dolby Digital Live is a 5.1 real time encoder found on the Xonar D1/X and up. It's mainly used for gaming though, as PC games do not have Dolby Digital tracks like a DVD.

Dolby Pro Logic II, is a mode found on the receiver. It upmixes any stereo sound to 5.1.

DTS, is the equivalent of Dolby Digital.

THX, is a audio reproduction standard designed by George Lucas' company, which was initially used for cinemas. Can also be found in home speaker equipment now.

PCM, stands for Pulse Code Modulation. It's what digital audio connections use, namely SPDIF and HDMI. SPDIF was designed in the 80s, before 5.1 came about. When using PCM, it is only capable of sending/receiving stereo. That is where Dolby Digital and DTS come in, they are used to encode and compress the stream, so that 5.1 can be sent along it. HDMI can use multi channel PCM, so does not require AC3/DD/DTS encoded audio in order for 5.1 to be sent over it.

 

[ANONANON]

Absolutely brilliant marsman. Thanks a lot for that buddy. That's answered a lot of questions for me. To be entirely honest, i'm just trying to get a half decent theatre setup for as cheap as possible. As long as the surround sound is convincing enough, then that'll do it for me, hell even sound technology from 10years ago is good enough for me.

What would give the best sound results do you think? Use SPDIF and Dolby Digital Live on the Xonar DX?, or use the analogue outputs from the sound card? It will be purely for watching films and nothing else.

 

[Marsman]

Well, there is no need to use Dolby Digital Live. However, should you buy a D1/X, you have it if you need it.

If you are going to buy a D1/X, then using analogue connections might be the better option. It really depends on how good the AV receiver is though. When using analogue connection on a sound card, that is handling the conversion of digital data into analogue sound. When using digital connection (SPDIF), the AV receiver converts the data into sound. The question is, which has the better DAC (digital to analogue converter), the AV receiver or the sound card. That really depends on how good the AV receiver is, and what it originally cost. A cheap new AV receiver will not have as good a DAC as a good mid range sound card such as the D1/X, but a AV receiver costing a few hundred will have a considerably better DAC.

Age is irrelevant really when it comes to quality, something that sounded good 10 years ago will still sound good today. It's mainly features that are missing from older AV receivers when compared to newer ones.

 

[ANONANON]

Whilst browsing the net i found this so came here to sort of answer my own question, then realised you posted a reply. In a nutshell, it confirms what you said about using analog over spdif. And here was me thinking spdif was the be all and end all.

Normal Dolby Digital uses 448kbit on DVD but can use 640K on BluRay.

Dolby Digital Live! uses 640kbit. Yes, it is the same as normal Dolby Digital.

But here is the problem. 5.1 audio is a 6-channel signal. 6 channels of 16bit/44.1KHz audio uncompressed takes up 4223kbit bitrate. With the best lossless compression algorithms we can reduce this by around 30% on average so that's still about 2963kbit required to send the full 6-channel sound.

Problem is, we cannot send this kind of bit-rate across the S/PDIF interface. So you need to encode it into a compressed and lossy codec. Dolby Digital needs to throw out some audio data to be able to shrink it down to 640kbit. To keep the story short, it starts by throwing out sounds that most humans can't hear anyways, but there is still a lot more that needs to be thrown out to finally reduce it to 640kbit.

You need to compress the original sound that your video game is sending out by 85% to make it fit within a 640kbit stream. That's a lot of compression. Even in the best case, looking at using as much lossless compression as is possible we would still need to further shrink the ~2963kbit compressed lossless stream down by 78% to make it fit in 640kbit.

When you use analog or HDMI none of this compression is needed and you can simply send the full 4223kbits to your amp

Analog it is then