I just wanted to chime in on the DTS vs AC3 thing.
One major difference between DTS and AC3 is the method of compression. Not necessarily dynamics (volume) but the actual data compression.
DTS is not about low bitrate, not at all. This is why the 5 channel DTS track on the original pirates movie sucks up 700+ MB of the disk. DTS concentrates on preserving the audio quality and yet fitting the same 5 channel data onto a physical piece of media. Theatre systems actually use regular CDs encoded with raw DTS for playback. A time code on the film keeps the audio in sync with the video.
AC3 is Dolby's version of a similar format. However, data compression is really the goal. AC3 is pre mp3 and AAC, and it shows. The artifacts that exist are pretty nasty. The maximum bitrate is 448 kbps on a DVD if you want your DVD to meet standards and play on most players. The reason the compression method was developed was to actually fit a packet of audio onto each frame of film. So the audio is encoded optically on the 35mm film itself. The problem for theatre versions is that the film over time wears out. Audio data is therefore lost. I've heard this in some really bad theatres that just run their print to death.
One thing that is nice is that DTS HD is really going to be HD. Normally we hear 16 bit 48 KHz audio on DVDs and on most BlueRay and HD-DVD releases. AC3 really wasn't well designed for anything more than 16 bit anyway. DTS HD isn't really even the same format as the original DTS. Now, with DTS-HD we can get 24 bit 192 KHz if we desire. Why in the world would we need this? Simple, we're human. Dynamics really do matter to us. When we experience normal life, we hear sounds that register very low, and some that are exessively loud. Digital audio at 16 bit just can't reproduce the dynamic range our ears prefer. However, 24 bit audio provides a massive improvement. With extremely good recording and playback equipment sounds as simple as a paper clip dropping on concrete or a train horn buzzing by can be reproduced at their original dynamic range. As for the KHz thing, it is simple. We comprimise on quality so often that we all don't know what we're missing.
To give you an idea, all of our phone calls on land line phones are at 8 KHz. This means that only low frequencies and up to a limited point are heard. Essentially we miss a ton of information. Digital audio capture is the reason for this loss. We have to limit the number of times we sample a sound. Well, high pitched sounds require that you sample them thousands of times per second in order to even remotely reproduce them. Since the human ear can only really hear to about 22 KHz (44 KHz digital) then what is the need for higher sampling rates? Simple, with 44.1 Khz or 48 KHz sampling we only scratch the surface of fidelity. With 96 KHz recording people generally notice that high frequency sounds have a "crisp" quality to them. That is simply because they've been sampled a proper number of times, and the full detail has been preserved. At 192 KHz, this same effect is experienced, but even for sounds outside of the human spectrum. Sonic research into marine life samples very high frequencies because some animals communicate at frequencies we can't even hear.
So, technobabble aside, the DTS has always been a higher quality sound, but Ac3 (Dolby Digital) takes up less space and can be placed directly on film if necessary. For consumers, most won't notice the difference. In theatres, it really is noticable. Theatres generally have better sound reproduction systems than we do at home. Some even have proper room environments, that really helps the situation.
I believe that if Disney were to use DTS-HD they would use a version that exists that can handle many more channels of unique audio. So, instead of just 5 channels, or 7 channels, maybe they use 64 channels. I've heard unreliable sources tell me that Soarin' uses 136 channels of distinct audio. Crazy part about Soarin' is that those channels are all either above you, below you, or to your sides. However, not much is really behind you. I'd imagine the use in a new ride system would not match traditional theatre use, as Soarin' demonstrates.
OK, I hope this clears up some of the confusion, or at least causes more curiosity about good audio. You know, we all get screwed left and right by the "consumer" quality of audio. Basically it is because most of us just don't know any better. That, and if we all could get the very high quality audio running at home, why would we visit IMAX and stadium seating theatres with amazing sound?
Ryan
Sources:
I've worked on many studio projects, been in radio for years, and geek out on audio in general. AC3 is something I've had the direct experience with, but DTS is so proprietary that even Apple's Final Cut Studio doesn't really support it.
DTS:
http://en.wikipedia.org/wiki/Digital_Theater_System
AC3 (Dolby Digital):
http://en.wikipedia.org/wiki/Ac3