difference between Dolby Digital 5.1 and DTS 5.1?

Both are lossy compression systems for 5.1-channel digital data streams. DTS compresses less and retains more of the original info, so generally sounds better.
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Actually the compression ratio for DTS and DD on DVD are the same. IIRC it something like 12:1 DTS got the reputation for using less compression back in the days of laser disc. On a laser disc DTS is something like 3:1 vs DD's 12:1.

Anybody who claims they hear something different is right, but it's not due to compression. It's different mastering. The soundtracks are done in different studio's by different technitions. The DD soundtrack is the same master track as the theater, the DTS is a remaster.

As an example, look and listen to Gladiator. You can argue the the dts and dd sond differnent, but you can't argue with the fact that the DD soundtrack won an Academy Award and the DTS did not.

Don't get me wrong, I like having both on my disc's.

The DTS track is always a larger file, how could they be the same? You will only need to strip both soundtracks to see this.

Dave

They are different encoding systems which do the same thing; i.e. produce 5.1 discrete channels.

DD 5.1 was first to market. It has a leg up because of that. DTS was later developed by technicians for Steven Spielberg's "Jurassic Park". In theory it is superior. It uses a higher data rate, 1.5 megabits/sec versus 384 kilobits/sec for DD 5.1 It also uses a lower compression ratio, 4:1 versus 10 or 12:1 for DD 5.1 The theoretical advantage is not often realized in practice, often because of limitations on the DVD itself which is used to hold the recorded material. This may disappear as DVD's which hold more information become more common. As long as your processor does both, everything is fine.