Dolby Digital encoding question (soundstorm/x-Mystique/x-plosion)

cokecan

cokecan

cokecan

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ive had soundstorm a couple fo years ago loved that for its DDL encoding, and i also have a mystique at the min that ive had for quite some time.

been havin this convo with my friend about dolby digital encoding and its makin me wonder.

my friends saying that all i got from soundstorm and my mystique is basically pro-logic 2, simply because you cant encode something into dolby digital that wasnt originally in dolby digital (i.e. music etc) which to me seems logical and why dvd's are dolby digital as they were originally encoded into 5.1, but then ive been tryin to explain to him that pro logic 2 and something thats been encoded into dolby digital by either the mystique or soundstorm does sound quite a bit different.

so, am i literally just listening to stuff in pro-logic 2 thats had the dolby digital name gaffa taped over it to disguise it :) lol or is it somethin else

can someone explain what it is ive been listenin to all this time???
 
It may well be Pro Logic II, I don't know, but I would have thought it would have mentioned it on the box if it was.

The only thing DDL cards do differently is compress whatever the card produces in to a single 5.1 AC3 stream. If anything it's worse than a good analogue card as it's being compressed (75 - 107kbps per channel)

Unless the soundcard had poor DACs you're not going to gain anything going Dolby Digital Live vs 5.1 Analogue output.

Having said that, for music listening Dolby Digital Live does kick-ass with the C-Media 8768+ (X-Mystique/TB Montego DDL), and it's all pretty academic until you get to really high end gear.

edit:

Some useful links:

Dolby Website
Dolby Digital Wiki
Pro Logic II Wiki

You probably already knew most of the stuff in the links already, but they're useful anyway.

Even Dolby don't try and make it out to be too special...just takes the sound, encodes it and outputs it over S/PDIF :)
 
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ok so accordin to them webbys, the dolby.com one inparticular, its saying that with the DDL encoding, its actually using the cues in the audio to produce a 5.1 sound from a 2 channel sound, sending the right sounds to the right speaker to match any on-screen action etc according to where the cue's are in the original sound, where as pro-logic 2 afaik just kinda clones the L and R channel in the surround L and R speakers and seperates the lower frequencies for a sub

if i'v eunderstood that right then it is actually dolby digital and pro-logic 2 then???

anyone wanna check that? :) lol
 
Dolby Digital Live: Takes each channel from the computer, encodes it in to one stream but each channel remains seperate and other than compression nothing is done to each channel. Exactly the same end result as using analogue cables on the back of the soundcard.

Dolby ProLogic II: Takes a stereo source and either:
  • Upmixes it blindly
  • Decodes extra channels that have been matrix encoded in to a stereo source

So you could have:
  • Stereo source encoded with ProLogic II
  • Pro Logic II decodes it and splits it back up in to 5.1 channels to output via the soundcard
  • Sound card takes the 5.1 channels, compresses and encodes the channels in to one single AC3 bitstream and outputs over S/PDIF.

Step 3 in there could quite easily be simply passing the 6 channels out via the 3 analogue ports on the soundcard and there'd be no conceivable difference in quality on most gear.

Whilst gaming:

  • Game Audio
  • Card processes sound in 5.1* channels
  • Card encodes 5.1 channels in to an AC3 bitstream as above, preserving each channel, and outputs it. Again, this could equally be done via analogue

What Dolby are saying the advantages of DDL are with the positional audio are that typically using S/PDIF output you're limited to stereo PCM audio, which if you then wanted surround sound you'd have to upmix on the amplifier/receiver. This obviously isn't ideal as the upmixer doesn't know where the original audio should be, but it takes a good guess at it.

Dolby Digital Live comes along and can preserve each channel over the S/PDIF cable, so therefore when a bullet goes flying over your head in game, with DDL you'll know exactly where it came from, and exactly where it's going. With upmixing, you'll just have to hope it guesses correctly.



*I'm not sure if there's actually a 0.1 channel involved at this stage, I think DDL takes the lower frequencies and makes it's own LFE channel
 
The only difference between soundstorm and analogue 5.1 PC sound is the packaging. DD live still encodes 6 discrete channels as if they were about to be passed to the analogue outputs, but instead are encoded as DD. It's just a different transfer mechanism in effect. I'm not sure what it does with stereo signals, but 5.1 signals from games will be passed as intended (perhaps with some bass management) to the decoder.
 
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