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THX Surround EX™ (Dolby Digital EX)
THX Surround EX,
also known as Dolby Digital EX, refers to the Dolby
Digital version of the new "6.1"-channel surround sound
format that extends the 5.1-channel surround sound format with one (or
two) additional speaker(s) located in the back of the audience (i.e., back
surround channel). THX Surround EX is actually a 5.1-channel
format with the back surround audio channel matrixed into those of the right and left surround. The back surround channel is
matrixed in similar fashion as the front center channel is matrixed into
the front right and left channels in the Dolby
Surround Pro-Logic format. As such, the back surround channel
is not discrete and
therefore THX Surround EX is not a true "6.1" format.
What about the extended surround "7.1" format? Well,
"7.1" is not a true surround sound format. Rather it
refers to home theater equipment manufacturers' proprietary
implementation of two back surround channels using the same back
surround audio signal that was discussed above. Usually, the audio
signal fed to the two back surround channels are identical, but some
manufacturers may choose to mix some information from the left and right
surrounds. Again, these are proprietary implementations that vary
across manufacturers and are not industry standards. The
use of two back surround speakers fills in the sound better from the
rear of the audience than single back surround speaker implementations.
To take advantage of THX Surround EX, you must have both:
(1) a DVD player and use one of the digital audio outputs (e.g., "Toslink"
optical or coaxial).
(2) a THX Surround EX decoder, usually a function of the receiver or
pre-amplifier. Look for the "THX
Surround EX"
words or logo on the faceplate. Receivers
featuring THX Surround EX decoding are still relatively expensive,
particularly those that comes with
six or seven channels of
amplification for the full frequency channels.
DTS Extended Surround Matrix is a competing
extended surround matrix
format, while DTS Extended Surround Discrete 6.1
is the only true discrete
6.1 format.
Also see: Surround Sound
Formats page for a full explanation, Dolby
Digital, DTS Extended Surround, DTS
Additional Information and References: Lucasfilm
THX Surround EX page, Dolby Digital home page
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