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In more than 30,000 cinemas and
10 million homes worldwide, Dolby Digital is the standard for 5.1-channel
surround sound.
Dolby Laboratories has now taken
Dolby Digital one step further with Dolby Digital EX. This new technology adds
an extra surround channel for an even more exciting, enveloping surround-sound
effect. This Guide explains how it works, and how you can hear it in your own
home.
Serious home theater fans will
appreciate the extra sense of dimensional detail and intensified involvement
that Dolby Digital EX adds to the already thrilling Dolby Digital 5.1-channel
listening experience.
In the Cinema
Dolby Digital Surround EX adds
to Dolby Digital 5.1 movie soundtracks a third surround channel, reproduced by
speakers positioned directly behind the audience. This extra rear surround
channel works with the usual left and right surround channels to produce an
intensified realism that draws you even further into the action. (See Figure
1.) As a result, alien creatures can circle all around you, fighter planes
can fly directly over you, and rain can pour down all around you more
realistically than ever before.
The additional back surround
information is encoded onto the regular left and right surround channels of
otherwise conventional Dolby Digital 5.1 soundtracks. In cinemas equipped with
Dolby Digital Surround EX decoding, the added information is reproduced as a
third surround channel. In cinemas without Surround EX decoding, the extra
information is played through the regular left and right surround channels, so
no information is lost.
Numerous films have been
produced in Dolby Digital Surround EX, and more are released every month. For a
list of current and upcoming Surround EX films, visit the "Movies and
Cinema" section of the Dolby Laboratories website, www.dolby.com.
In the Home
Feature films originally
released in Dolby Digital Surround EX carry the encoded third surround channel
in their subsequent DVD releases, as well as onto 5.1-channel digital satellite
and terrestrial TV broadcasts. If your home theater system has a receiver or
preamp/processor with Dolby Digital EX decoding-the home version of Surround
EX-you can hear Surround EX soundtracks as they were meant to be heard, with the
increased realism created by the extra surround channel. As in the cinema, with
regular 5.1-channel Dolby Digital playback no sonic information is lost
(although you'll miss out on the heightened realism).
Newer Dolby Digital Surround EX
soundtracks contain a digital flag which can automatically activate the EX
decoding in a receiver or preamp/processor. For titles released prior to late
2001, however, you need to turn on the EX decoding manually.
Although Dolby Digital EX
decoding is intended for soundtracks that have been Surround EX encoded, you may
find that some regular 5.1-channel soundtracks sound quite good with EX decoding
switched on. Its effectiveness varies from soundtrack to soundtrack, so be sure
to try it both ways.
Adding Dolby Digital EX
to Your System
A Dolby Digital EX home theater
system closely resembles a conventional 5.1-channel system. The differences are
the addition of EX decoding, one or two more surround speakers at the rear, and
one or two more amplifier channels.
With receivers and
preamp/processors equipped for Dolby Digital EX, the additional decoding is
built in along with conventional Dolby Digital 5.1 decoding. Some receivers also
build in extra amplification for the third surround channel, while with others
you need an extra, standalone amplifier. If you have a preamp/processor, you can
either add another single- or two-channel amplifier to your existing setup, or
opt for a six- or seven-channel amplifier to consolidate all amplification in
one unit. If you add an extra amplifier, it should be of similar design and
power rating to your existing amplifier or receiver.
For Dolby Digital EX playback,
as with regular 5.1 playback, place the left and right surround speakers to the
sides of, or slightly behind, your listening position. For the third surround
channel, place an additional surround speaker, or, preferably, an additional
pair of surround speakers, directly behind the listening area, as shown in Figure
2.
If you use a single rear
surround speaker, center it behind the listening area at the same height as the
side surround speakers, preferably above ear level. If you use two back surround
speakers, which give a more diffuse and natural surround effect, they should be
at least four feet apart (creating an included angle of about 90 degrees to the
listener), also centered behind the listening area and at the same height as the
side surround speakers.
The ideal is to have identical
speakers for all the surround channels. They should at least be of the same
brand and of similar design. They can be monopolar (direct-radiating), bipolar,
or dipolar designs, depending on your preference and room acoustics.
Adjusting Your
Dolby Digital EX System
Once your additional surround
speakers and amplifiers are connected, adjusting a Dolby Digital EX system for
maximum performance is much like adjusting a conventional Dolby Digital system.
First, using an onscreen menu
(Figure 3) or front-panel controls, depending on your particular receiver or
preamp/processor model, "tell" your receiver or preamp/ processor that
you have a center surround speaker or speakers.
Second, "tell" your
receiver or preamp processor whether the additional speakers are Small or Large,
as an indication of how much bass they can reproduce.
Choose Small if they are
bookshelf or wall-mount systems without internal amplification; choose Large if
they have built-in powered woofers, or are floorstanding, tower-type units.
Third, set the delays for the
extra surround speaker(s). Many receivers and preamp/ processors let you enter
the distance to the speakers in feet or meters, then calculate and set the delay
automatically. If yours requires you to enter the delay in milliseconds (ms),
subtract the distance in feet to the left surround speaker from the distance to
the left front speaker to get the proper setting in milliseconds. Measure these
distances from your usual listening position.
Finally, activate the internal
test-tone generator in the receiver or preamp/ processor, and adjust the level
of each channel so that all the speakers play at the same level. You can do this
by ear, or you can use a sound-pressure level (SPL) meter for a more precise
adjustment. For specific instructions, see the processor's owner's manual.
All
Dolby Digital related content is Copyright © 2002 Dolby Laboratories, Inc. All
rights reserved.
Dolby and the double-D symbol are registered trademarks of Dolby Laboratories.
All other trademarks are the property of their respective owners.
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