A LISTENER'S GUIDE
TO DVD-VIDEO
DVD-Video doesn't just offer a better picture. It also provides vastly
improved sound-and a lot more of it. Up to eight soundtracks, including
different-language versions of a movie, can be included on the same disc. What's
more, the soundtracks can carry anything from mono sound up to 5.1-channel
surround sound, and use different digital audio coding technologies.
Soundtrack Formats
Most DVD-Video discs feature a mono, two-channel
or 5.1-channel Dolby Digital soundtrack. Many two-channel soundtracks,
particularly on discs of movies, are Dolby Surround encoded for four-channel
playback over systems equipped with Dolby Surround Pro Logic decoding. Older
movies, of course, often have mono soundtracks.
Sound Modes
Many DVD-Video releases display icons that show the
number of audio channels in a soundtrack and the channel configuration. An
example of these sound mode icons is shown in Figure
1.
Some 5.1-channel decoder units and A/V receivers have playback mode displays
based on these same icons. Some discs provide a variety of soundtracks using
different sound modes. A movie disc, for example, might use 5.1-channel Dolby
Digital for its English track, and Dolby Surround for other languages.
Digital Audio Types
A DVD-Video soundtrack can be of one of several
audio types, based on different digital audio coding systems-and soundtracks of
different audio types can be included on same disc.
Dolby Digital is categorized as a "mandatory" audio type, meaning it can be
the only one used on a disc. Those that are categorized as "optional" can be
used only when at least one soundtrack of a "mandatory" type is on the disc as
well. Figure
2 lists the various audio types used on DVD-Video discs.
Because all DVD-Video players are equipped with Dolby Digital decoding as
standard, most DVD-Video titles have only a mono, two-channel or 5.1-channel
Dolby Digital soundtrack as previously noted. Packaging for these titles usually
displays the  logo.
Additional indicators or logos are displayed if soundtracks of more than one
audio type are present. The Dolby Digital track on such discs may be identified
by the  icon combined with a sound mode icon.
Figure
3 shows an example of a disc with four soundtracks utilizing different sound
modes and digital audio types.
Playback
Most DVD-Video players provide two-channel analog outputs
plus a digital audio output.
As shown in Figure
4, the two-channel analog output is for connection to a TV, a two-channel
stereo system, or a home theatre system with Dolby Surround Pro Logic decoding.
The player will automatically create a Dolby Surround encoded, two-channel
version of 5.1-channel Dolby Digital soundtracks. For mono playback, some
players can also create a mono version at the listener's option.
As shown in Figure
5, the digital output is for connection to an external unit, such as an A/V
receiver, with 5.1-channel Dolby Digital decoding.
Some players, as shown in Figure
6, have built-in 5.1-channel decoders for connection to a "5.1- channel
ready" receiver. External 5.1-channel decoders, however, provide the greatest
flexibility, and often superior sound as well.
About Surround Sound
Dolby Surround delivers four-channel surround
sound via regular stereo VHS video tapes, TV and FM broadcasts, laser discs,
DVD-Video and DVD-ROM discs, video games, and CDs. Four channels (left, center,
right, and surround) are encoded into two-channel soundtracks, then recovered on
playback by means of a Dolby Surround Pro Logic decoder. (Figure
7)
Dolby Digital can deliver 5.1-channel sound from DVD-Video and DVD-ROM discs,
laser discs, and digital TV broadcasts, satellite transmissions, and cable
systems. It differs from Dolby Surround by providing two separate surround
channels for greater realism, and an additional ".1" or "LFE" channel for
low-frequency (bass) special sound effects. (Figure
8)
The LFE channel is sometimes incorrectly identified as the "subwoofer"
channel. While a subwoofer can be helpful in reproducing low bass in general, it
is not necessary to have one if one or more of the speakers in the playback
system have extended bass response. Without a subwoofer, the LFE channel's bass
effects can be directed to those speakers with extended bass. Furthermore, not
all multichannel soundtracks have the ".1" channel; it is used primarily for
explosions, rumbles, and the like on movie soundtracks, and is not present on
all programs.
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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