Dolby Digital 5.1
Dolby Digital 5.1 is a digital compression system allowing a total of five completely independent sound channels to be played from a DVD player, satellite decoder or digital cable: the left and right channels, the central channel, the two rear channels and a special channel for low frequencies, LFE (Low frequency effects). This system keeps the dynamics and bandwidth of the original cinema theatre soundtrack distributed under the "Dolby SRD" (Spectral Recording Digital) trademark. The result is significantly better than using Dolby Prologic I or II, since the system reproduces six channels (including the low frequency channel) that are totally separate right back to the original recording.
Dolby Digital EX and DTS ES: These are evolved versions of the two previous standards. Now the sound is no longer broadcast over five main channels, but six! An extra effect channel is inserted between the two rear loudspeakers requiring an amplification channel and an extra speaker of course. The process is currently only used for a small number of films where particular attention has been paid to the cinema sound. In suitable premises, adding an extra surround channel makes the film even more spectacular.