Star Wars: Episode I was the first of a number of films using an additional rear
channel routed to the array of speakers along the back wall of a cinema. In the
cinemas, this back channel is not a discrete channel, but is matrixed into the left
and right surround channels, much as the center front channel was matrixed into
the left and right front channels in earlier matrix optical surround formats. This
matrixed back channel is embedded in the soundtrack printmaster, so finds its
way into all cinema digital sound formats. DTS uses the name "ES" on its cinema
decoder; others call the process “Surround EX”. Either set of letters stands for
When the film soundtrack is transferred to DVD, the matrixed back channel again
automatically appears in the 5.1-channel soundtracks on the disc. However, DTS,
with its greater bandwidth, is able also to offer a fully discrete back channel which
can be recovered by a new generation of decoders. Such soundtracks are fully
compatible with existing 5.1-channel DTS decoders; on a 5.1 setup, the back
channel information would be heard in and between the left and right surround
speakers. Thus "ES" is the general term for DTS tracks with a back channel, and
"ES 6.1 discrete" is the particular case where the back channel is discrete.
To summarize about DTS-ES for the home:
ü The back channel is always matrixed into the LS and RS channels.
ü A discrete back channel can optionally be encoded as well.
ü A DTS-ES 6.1-discrete decoder will play the discrete back channel.
It will also subtract the discrete back channel out of the matrixed LS
and RS channels, restoring the LS and RS channels as
ü Any DTS-ES track, discrete or not, is fully compatible with 6.1-
matrix decoders because the matrixed tracks are always present.
ü Any DTS-ES track is fully compatible with 5.1 decoders because
the back channel information is matrixed into the LS and RS
channels and will thus be heard in and between the LS