There\'s Dolby Digital, which is probably the most common thing used in theaters. Of course there\'s also Dolby EX, but that is just an extra center-rear channel.
SDDS-Sony Dynamic Digital Sound which offers a left-center and right-center channel that none of the others offers. However many people find it difficult to maintain in the theater
DTS- Digital Theatre Systems- This is where the soundtrack is kept entirey on a compact disc. The DTS reader follows a timecode on the movie print, thus keeping all the dialog and music in sync.
THX-Was designed by Lucas to form a series of standards that go above and beyond NATO standards. This certification includes what the walls of the theater are made out of, what kind of screens it has, where the speakers are, and what kind of equipment is used. Dolby Digital, SDDS, and DTS are all THX certified as being quality ways to reproduce sound.