DTS and Dolby Digital through S/PDIF

[dohanc]

I have a question that I can't find any good websites that really explain it. I am very familiar with 2-channel audio however have no experience so far with multichannel. I listen to music and watch movies via my computer. I am getting a new sound card (M-Audio Revolution 5.1 or 7.1) which seems to be one of the best HQ audio cards. My question is about the S/PDIF output.

I am getting a new receiver that decodes Dolby Digital, DTS, etc. I would like to send a digital out of the sound card to the receiver and have the receiver do the decoding. Easy enough so far. My question is if I get a 5.1 sound card, will the S/PDIF output still be able to output 7.1 through the S/PDIF? I know it will not be able to decode 8 channels and send them through its 6 channel analog outs, but the S/PDIF I believe is just a direct compressed digital signal from the movie be it 2, 5 or 7 channels. Any help with this subject? Can't find much directly related to it on the internet. Thanks

 

[MDS]

S/PDIF defines the communication protocol and packet format of the audio. Both digital coax and optical use S/PDIF.

If the soundcard has a digital out and allows you to simply pass the digital signal to that output, then yes you could send a 7.1 signal from the soundcard to a receiver. However, there are exactly ZERO discs that have 7.1 discrete channels. 5.1 will be no problem. For some cards, like the Soundblaster Audigy, you have to enable digital output in the mixer applet that comes with card. The MAudio is probably similar.

 

[Leprkon]

I am getting a new receiver that decodes Dolby Digital, DTS, etc. I would like to send a digital out of the sound card to the receiver and have the receiver do the decoding. Easy enough so far. My question is if I get a 5.1 sound card, will the S/PDIF output still be able to output 7.1 through the S/PDIF? I know it will not be able to decode 8 channels and send them through its 6 channel analog outs, but the S/PDIF I believe is just a direct compressed digital signal from the movie be it 2, 5 or 7 channels. Any help with this subject? Can't find much directly related to it on the internet. Thanks

since 7.1 is an imaginary (ok, simulated) signal, it should be no problem. Your receiver will do the decoding, ripping some pieces of the 5.1 surround sound out to make your 6th and 7th channels.

 

[dohanc]

Anonymous, that was my other question. How many discs are actually using DTS ES or Dolby Digital EX (7.1). Not suprised to learn zero.

Leprkon: I believe what you are talking about is some "surround mode" which simulates a 6 and 7th speaker in which sending a 5.1 signal will be create a 7.1 signal. But is DTS ES or Dolby Digital EX doing this or is it really intended to save some discrete 6th and 7th channel encoded on it?

Depending on the answer of that question, I would then ask do I really need a 7.1 card? A 7.1 decoder on a receiver may be worth it (assuming 7 channels is worth it which is a different subject/thread) but if the 5.1 card can actually output the 7.1 S/PDIF signal then the only different is the 7.1 card actually has 2 more analog outs. Does it make sense that a 5.1 card should be able to output 7.1 S/PDIF?

The M-Audio has a dedicated digital coax out. It can pass through encoded data. Only benefit of geting the 5.1 as opposed to the 7.1 is it is slightly less CPU intensive which would benefit video decoding.

 

[Leprkon]

Leprkon: I believe what you are talking about is some "surround mode" which simulates a 6 and 7th speaker in which sending a 5.1 signal will be create a 7.1 signal. But is DTS ES or Dolby Digital EX doing this or is it really intended to save some discrete 6th and 7th channel encoded on it?

Depending on the answer of that question, I would then ask do I really need a 7.1 card? A 7.1 decoder on a receiver may be worth it (assuming 7 channels is worth it which is a different subject/thread) but if the 5.1 card can actually output the 7.1 S/PDIF signal then the only different is the 7.1 card actually has 2 more analog outs. Does it make sense that a 5.1 card should be able to output 7.1 S/PDIF?

DTS-ES and Dolby Digital EX are both simulated for channels 6 and 7. They are not discrete channels and are created inside the receiver by sound processing algorithms.

I can't comment on cards.. if you are talking computer "audio" cards... I know nothing about them as far as they appy to HT. BMXTRIX or Mudcat will be alot better people to talk to about those.

 

[MDS]

Dolby Digital EX and DTS-ES (matrix and discrete) are 6.1 channel formats, not 7.1. There are no discs with 7.1 discrete channels in any format at this time.

If the sound card says it is 7.1, then it creates the 6th and 7th channels from 5.1 or 6.1 material, in the manner that Dolby Prologic IIx does. I would bet it actually uses DPLIIx although it may use another proprietary algorithm of their own making. If you have the card simulate 7.1 from a 5.1 or 6.1 source, it can send all 8 channels out the 7.1 analog outputs and you could connect it to the 7.1 analog inputs on a receiver. Digital out however will no longer work once the signal has been changed from 5.1 to 7.1 (its the same thing as when you have your dvd player do the decoding of 5.1 - it turns it into 2 channel. You can then send the 2 channel output digitally (that's what the PCM setting on the player controls) but the original 5.1 or 6.1 is long gone.)

So you can send 5.1 or 6.1 digitally out the digital coax to be decoded by the receiver or you can have the card downmix it to 2 channel and send it out the digital coax. If the card does any processing to turn 5.1 or 6.1 into 7.1, you can only send it out the 7.1 analog outs.

 

[dohanc]

So it appears that there is absolutely no use for a 7.1 sound card as I will be using the digital out and have the receiver decode it (create the 7th channel). The last post was helpful, but you say that you can output 6.1 through S/PDIF. Is the 6th channel in 6.1 channel a discrete channel and not "created" from the other channels? If it is, how many movies are actually using this 6.1 format? If it is a discrete channel then the 7.1 card would have some added benefit. If it's just another synthesized channel then the receiver can do that and the 5.1 card is exactly the same for my digital output purpose. Thanks.

 

[MDS]

I don't know off the top of my head how many movies use DD-EX or DTS-ES but I suspect it is near a hundred or more by now. Check out sites digitalbits.com that do dvd reviews.

The only 6.1 format that is discrete is DTS 6.1 discrete and even that is not truly discrete. There are 6.1 separate channels, but the 6th channel is also matrixed into the L/R surrounds. On decoding, that info is cancelled out from the L/R surrounds so you don't have duplicate info in the side surrounds and the 6th back channel. That is why most people don't consider it to be truly discrete.

DTS-ES Matrix and DD-EX are 6.1 formats, but the 6th channel is matrixed into the L/R surrounds and is extracted on playback. So there are really only 5.1 discrete channels.

 

[dohanc]

Ok so I got the formats down. So besides the analog outs of the 6th and 7th channel on a 7.1 sound card, are there any negatives to getting just the 5.1 card? The other thing that hasn't been mentioned is how to actually select the correct decoding format on the receiver. Does the receiver do this automatically or do I have to select this manually.

So from what I gathered so far, there is no difference to getting a 5.1 sound card as opposed to a 7.1 card assuming I am using the receiver decoder with a S/PDIF link as the 6th and 7th channel are synthesized from other discrete channels.

 

[MDS]

Yep, if you are going to send the signal digitally to the receiver and let the receiver use a surround mode like Dolby ProLogic IIx to simulate 7.1, then there is no reason to buy the 7.1 card.

As far as selecting the surround processing algorithm, most receivers let you pick one based on the input signal format and will remember it so that the next time it sees the same type of signal it will automatically switch to the mode you used last. You can change it manually at any time too.

For example, on my Onkyo, I leave it set to DPLII Music. If the input signal is analog or DD 2.0, it automatically switches to the DPLII Music mode. I can also manually change it to DPLII Movie or Neo:6 or All Channel Stereo, etc. at any time.

 

[stand]

Hi all... I have the same audio card - M-Audio Revolution 5.1, and my problem is that I NEVER can make it pass a Dolby Digital signal to my receiver. I use the digital coaxial output of the card with a good cable and my receiver always says its a DTS signal, not Dolby Digital... At that same time I play the same disc on my DVD player and my receiver immediately gets the Dolby Digital signal and DD led lights up...

Anyone got a clue? Maybe this card is not capable of sending Dolby Digital signal through its coaxial digital output?