What Is Surround Sound?
Surround sound refers to the use of multiple
audio tracks to envelop the movie watching or music listening
audience, making them feel like they're in the middle of the
action or concert. The surround sound movie soundtrack
allows the audience to hear sounds coming from all around
them.
Where does the sound come
from?
True surround sound formats rely on dedicated
speakers that literally and physically surround the
audience. There is a center speaker which carries most
of the actors dialog, and part of the soundtrack.
There are left and right front speakers that carry most of the
soundtrack (music and sound effects), and may carry parts of
the dialog (when the director wants to intentionally off-set
the source of the dialog to either side, from its default
dead-center screen location). Then there is a pair of
surround sound speakers that are placed to the side (and
slightly above) the audience to provide the surround sound
and ambient effects. Finally, a subwoofer can be used to
reproduce the low and very low frequency
effects (LFE) that come with certain movies.
Dolby
Digital™
Dolby
Digital (formerly known as Dolby AC-3, where AC-3 is
short for audio coding 3) is the de facto surround sound
standard in today's home theaters. It is the surround
sound format used in thousands of movie theaters today.
And, since about the mid-1990's, it has become available for
home theater use by consumers. Today, a large
percentage of the DVD-Video titles come with Dolby Digital
surround sound. Dolby Digital content first appeared on
LaserDisc, since DVDs only emerged in the Spring of
1997. (Hi-Fi VHS still only supports up to
Dolby
Surround Pro-Logic.)
Not only is Dolby Digital the
standard for DVD-Video, but it is also part of the High
Definition TV (HDTV) standard. It is used in
pay-per-view movies and digital TV channels of digital
satellite broadcasting (e.g., DIRECTV system). Dolby
Digital is the successor to Dolby Surround Pro-Logic.
The Dolby Digital surround sound format provides up to
five discrete (independent) channels (center, left, right,
surround left, surround right; giving it the "5" designation)
of full frequency effects (from 20 Hz to
20,000 Hz), plus an optional sixth channel dedicated for low
frequency effects (LFE), usually reserved for the subwoofer
speaker. The low frequency effects channel gives Dolby
Digital the ".1" designation. The ".1" signifies that
the sixth channel is not full frequency, as it contains only
deep bass frequencies (3 Hz to 120 Hz). Readers should note that not all
Dolby Digital soundtracks have 5.1 channels of audio.
Those that are have the designation "Dolby Digital 5.1".
Since Dolby Digital is a flexible surround sound format that
supports up to 5.1 channels, Dolby Digital soundtracks
could have one channel of audio (mono, designated as "Dolby
Digital 1.0"), two channels of audio (stereo or Dolby Surround
Pro-Logic, designated as "Dolby Digital 2.0"), or five
channels of audio (designated as "Dolby Digital 5.0").
In fact, the Dolby Digital 2.0 soundtrack is required
for all Region
1 (U.S. and Canada) DVDs.
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The consumer must use an audio component which has a Dolby
Digital decoder (and amplifier) in order to process and route
the channels of sound and drive the loudspeakers. Most
Audio/Video Receivers today have such decoders and amps with
the proper loudspeaker connections.
DTS Digital
Surround™
An alternative and
competing format to Dolby Digital is DTS Digital
Surround, or just "DTS". Like Dolby Digital, DTS is
another 5.1-channel surround sound format that is
available in movie theaters, and as an optional
soundtrack on some DVD-Video movies for home theater
viewing. But unlike Dolby Digital, DTS is not a standard
soundtrack format for DVD-Video, and is not used by HDTV or
digital satellite broadcasting.
The primary advantage of DTS is that it offers
higher data rates than Dolby Digital, leading many home
theater enthusiasts to claim that DTS is better than
Dolby Digital in sound quality. The down side is that a
DTS soundtrack uses more of the disc's data capacity due to
its higher data rate. This fact plus the fact that DTS
is not a standard soundtrack format for DVD-Video makes DTS an
optional 5.1-channel surround format that is actually
available on few DVD-Video movies. There are far more
DVD-Video titles with Dolby Digital soundtracks than there are
those with the DTS surround sound format.
Dolby Surround
Pro-Logic™
Dolby Surround Pro-Logic emerged in home
theater systems in the early 1990's. It became the
surround sound standard for Hi-Fi VHS, and is still the
standard for today's analog TV broadcasts, since the Dolby
Surround Pro-Logic signal can be encoded in a stereo analog
signal. If you have an "older" Dolby Surround Pro-Logic
receiver, you can still enjoy movies from DVD-Video, since all
DVD-Video players down-mixes the Dolby Digital information to
the Dolby Surround Pro-Logic format, and outputs the signal as
a stereo audio pair.
Extended
Surround formats:
Dolby Digital EX™, THX Surround
EX™ & DTS Extended Surround™ (DTS-ES™)
Just when you thought 5.1-channel Dolby
Digital and DTS surround sound were enough, there are two new "Extended Surround" formats, namely THX
Surround EX™ and DTS Extended
Surround™ (or DTS-ES™ for short).
The THX Surround EX format
is jointly developed by Lucasfilm THX and Dolby Laboratories, and is
the home theater version of "Dolby Digital Surround EX™", an
Extended Surround sound format used by state-of-the-art movie
theaters. Lucasfilm THX licenses the THX Surround EX
format for use in receivers and preamplifiers. And as of
November 2001, Dolby Laboratories has begun to license what is
THX Surround EX under its own name, Dolby
Digital EX™, for consumer home theater equipment.
(Since THX Surround EX and Dolby Digital EX are equivalent, we
will refer to THX Surround EX and Dolby Digital EX
interchangeably, with preference for the former since that
name has been around longer.)
THX Surround EX is the Extended Surround
version of Dolby Digital 5.1, while DTS-ES is that of DTS
5.1. The difference between the new
Extended Surround formats and their 5.1-channel surround sound
counterparts is the addition of a surround back
channel, whose corresponding speaker is placed
behind the audience. This allows certain
soundtrack effects to be presented behind the audience,
thereby achieving more enveloping and complete 360° surround
sound. (Remember that in the 5.1-channel surround sound
formats, the surround speakers are placed one on each side of
the audience - not behind them.) Additionally, while the
Extended Surround sound format
calls for one surround back channel, two surround back
speakers are generally recommended for better
envelopment. Acknowledging this widely accepted industry
position, some high-end receiver manufacturers have introduced
"7.1-channel" capable receivers, with decoding and sometimes
amplification for the two extra surround back channels.
Both THX Surround EX and DTS-ES
Matrix surround sound encode the surround back channel
information into the surround left and surround right channels
(similar to the way the center channel is encoded for Dolby
Surround Pro-Logic). This cross-channel encoding is
referred to as matrix encoding, since the surround back
channel is encoded and later decoded (or derived) from those
of the surround left and surround right channels.
Because of this matrix encoding scheme, the surround back
channel is not a true discrete channel and is
technically considered a 5.1- channel format. And for
this reason, they are sometimes referred to as "Dolby Digital
5.1 EX" or "DTS 5.1 ES".
A true
6.1-channel format: DTS-ES Discrete 6.1
DTS-ES can optionally support a fully discrete
surround back channel. That is, the surround back
channel has it own data stream and is truly independent from
those of the surround left and surround right channels.
This true 6.1-channel format is appropriately called DTS-ES Discrete
6.1 (in contrast to its matrix counterpart, DTS-ES
Matrix). And as with DTS-ES Matrix, this discrete format
is better realized with two surround back speakers.
The Extended Surround formats are completely
backwards-compatible with their 5.1-channel
counterparts. That is, THX Surround EX is backwards
compatible with Dolby Digital 5.1, and DTS-ES Matrix and
DTS-ES Discrete 6.1 are backwards compatible with DTS
5.1. Additionally, DTS-ES Discrete 6.1 is backwards
compatible with DTS-ES Matrix. In order to hear the
matrix Extended Surround formats, you will need a THX Surround
EX, DTS-ES Matrix, or a generic "6.1-channel" decoder in your
receiver or preamplifier and use the digital audio output of
your DVD player. To hear DTS-ES Discrete 6.1, you will
need a DTS-ES Discrete 6.1 decoder in your receiver or
preamplifier. In any case, you will also need six or
seven channels of amplification, and one or two extra speakers
for the surround back channel. Rest assured, you can
still use your existing (or a soon-to-be-purchased) DVD-Video
player, as long as it features Dolby Digital and DTS digital
output.
Movies and DVDs
featuring Extended Surround
"Star
Wars: Episode 1 The Phantom Menace" is the very first
movie to feature Dolby Digital Surround EX format. The first DVD
with THX Surround EX is "Austin
Powers: The Spy Who Shagged Me", while the first with
DTS-ES 6.1 Discrete is "The
Haunting". "Terminator
2: Judgment Day (Ultimate Edition)" DVD features both THX
Surround EX and DTS-ES Discrete 6.1. Proper use and
placement of surround sound speakers are key to getting the
most out of surround sound systems.
Home
Theater Surround
Sound
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