Surround Sound Formats: What You Need To Know
Dolby® Digital is, without a doubt, the most popular surround sound
format out there. Yet there are several other surround formats on the
market, too. Because most people, from surround sound novices to A/V
experts, find new formats a little confusing, we've provided a quick
description of how each format works. You can also take a look at our surround format chart for an even faster summary.
Dolby Pro Logic: The basics
Dolby Pro Logic® was the home theater audio standard for years, and is still a common form of surround sound. It provides four channels
of sound: three full-range channels which play through the front right,
front left, and center speakers, and a fourth channel of
limited-bandwidth sound which is shared by two surround speakers. Dolby
Pro Logic is a "matrixed" multichannel system, meaning that some
channels are actually derived from other channels — in this case, the
center channel and surround channels are created from the exisiting
left and right channels.
Dolby Pro Logic sound starts as four channels, and is encoded to
two channels for transfer. This encoded signal is easily carried via
videotape or stereo TV broadcast. During playback, your receiver
converts the Dolby-encoded signal back to 4 channels.
How Dolby Pro Logic works
Why Dolby Pro Logic II?
Dolby Pro Logic II improves on original Dolby Pro Logic with special circuitry that creates a convincing 5.1-channel experience with stereo, full-bandwidth surround channels!
And yet Dolby Pro Logic II uses the same Dolby Surround-encoded and
stereo sources as Dolby Pro Logic. Receivers with Dolby Pro Logic II
give extra intensity to the 12,000 VHS movies with Dolby Surround and
the limitless TV broadcasts and music available as stereo sound.
Dolby Digital: A higher level of realism
Dolby® Digital quickly established itself as a
reigning surround format, largely thanks to DVDs. Although Dolby
Digital, strictly speaking, is a particular method of encoding audio
information digitally, the term is often used to refer to 5.1-channel
audio — its most popular form. In discussing Dolby Digital surround
sound, we'll be focusing on this multichannel format.
Unlike Pro Logic, Dolby Digital 5.1-channel audio is a "discrete"
multichannel surround sound system. Discrete means that the sound
information contained in each of the six available channels is distinct
and independent from the others. These six channels are described as a "5.1-channel" system,
because there are five full-bandwidth channels with 3-20,000 Hz
frequency range for front left and right, center, and surround, plus
one "low frequency effects" (LFE) subwoofer channel devoted to
frequencies from 3-120 Hz.
Advantages to Dolby Digital include the following:
- Dolby Digital is the chosen multichannel digital audio format for DVDs and HDTV
- any receiver with Dolby Digital decoding can also decode Pro Logic
- six discrete channels; sounds can be placed much more
precisely, for improved dialogue clarity, soundstage size,
spaciousness, and realism
- you get stereo surround channels; you can hear separate off-screen sounds to the left rear and right rear simultaneously
- you get a dedicated subwoofer channel, for plenty of deep bass
- thanks to digital encoding, you enjoy greater accuracy
How Dolby Digital works
DTS: Another 5.1 surround option
Like Dolby Digital, DTS® provides 5.1 channels
of digital audio. However, DTS uses less compression than Dolby
Digital. As a result, some say that the sound produced by DTS is
slightly more accurate than the sound produced by Dolby Digital.
The down side is that most DTS DVDs don't have as much room for
extra features (like commentaries, foreign languages, and multiple
versions of the movie). Also, there are very few DTS DVDs or CDs
available, compared to the number of Dolby Digital DVDs.
THX Surround EX and Dolby Digital EX
These playback formats are a collaboration
between THX and Dolby Labs designed to give surround sound improved
directionality. They do essentially the same exact thing, both adding
another one or two "back surround" speakers to the speakers already
present in a 5.1-channel system in order to provide a more fully 360°
wraparound experience. The added channels, rather than being discrete,
simply share a matrixed channel of sound composed of information from
the regular surround channels.
Currently, many newer DVDs are encoded for Dolby Digital EX, and
have that extra channel of surround information ready to go. Also, if
you're playing a regular Dolby Digital 5.1-channel DVD, a THX Surround
EX™ or Dolby Digital EX decoder will simulate 6.1- or 7.1-channel
surround by processing the audio information in the regular surround
channels and sending it to your back surround speaker(s).
DTS-ES: 6.1 surround from DTS
DTS-ES™ uses existing digital multichannel technology to deliver the "5.1" channels of regular DTS, plus it adds a discrete,
full-bandwidth back surround channel. That additional channel may be
played through one or two speakers. Because that sixth channel of
full-bandwidth sound is discrete, rather than matrixed, some consider
DTS-ES an improvement over THX Surround EX and Dolby Digital EX.
Currently, only a few DVDs are encoded with 6.1-channel DTS-ES sound.
Click here for our surround sound formats chart.
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