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article last updated on
12.11.2002 | printer-friendly
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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, and
plays a large part in realizing what movie makers call
"suspended disbelief". "Suspended
disbelief" is when the audience is completely captivated by the
movie experience and is no longer aware of their real-world
surroundings.
True surround sound formats rely on dedicated speakers that literally and physically surround
the audience. There is one center speaker which carries most
of the dialog (since the actors usually speak while making their
on-screen appearance), 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). There is a pair of
surround sound speakers that is placed to the side (and slightly
above) of 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 (e.g., the foot-stomping
bass effects in "Jurassic Park" and "Godzilla").
A
typical surround sound home theater system
(picture courtesy
of Dolby
Laboratories)
There are virtual surround sound algorithms (e.g.,
Sound Retrieval System [SRS] and other proprietary algorithms) that make use of only two left and
right speakers and psycho-acoustics effects to emulate true
surround sound formats. While we think the result is a more
expansive soundstage with better ambiance, we have not heard a virtual
surround sound implementation that comes anywhere close to
resembling a true surround sound system. For the purposes of
this discussion, we shall focus only on the true surround sound
formats (that is, those that rely of multiple dedicated speakers).
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. (Incidentally, 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 new 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. To learn more about Dolby
Digital, read this Dolby
Digital reference page.
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. For additional information
about DTS, read this DTS
reference page.
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, at the
leading edge today 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". To refer to
these matrix encoded Extended Surround formats as 6.1-channel would
be wrong. (When we use quotes, as in the
"7.1-channel" reference above,
we are recognizing that it may not be a true discrete 7.1-channel
system.)
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. So our
comment above about high-end manufacturers implementing
"7.1-channel" receivers and preamplifiers for this
purpose still holds true.
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
the new Dolby Digital Surround EX format (though Dolby Digital Surround EX
playback is offered only in the finest state-of-the-art movie theaters).
Even up until now, only a handful of movies have
been released with the new Dolby Digital Surround EX format.
For lists of theatrical movie titles with Dolby Digital Surround EX
soundtrack, click here
for previous
releases and here
for upcoming
releases.
Likewise, only a few DVDs
released to date have either THX Surround EX or DTS-ES.
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. If you're interested in DVDs with Extended Surround sound, our DVD New
Releases and Upcoming Releases
pages designate those DVD titles that are available in either THX
Surround EX or DTS-ES.
Additional Info: Proper
use and placement of surround sound speakers are key to getting
the most out of surround sound systems. For a more detailed
discussion of proper use and placement of speakers for a home
theater environment, read this authoritative
guide from Dolby
Laboratories.
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