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Surround sound formats
Below is a brief description of the main surround sound
formats you’ll find on DVDs, satellite, cable and
terrestrial broadcasts, and video cassettes.
Dolby
The Dolby technologies are explained below. See
www.dolby.com for more detailed information.
Dolby Digital
Dolby Digital is a multichannel digital audio coding
system widely used in cinemas, and in the home for DVD
and digital broadcast soundtracks. It can deliver up to six
discrete audio channels, comprising five full range
channels and a special LFE (low frequency effects)
channel used mainly for deep, rumbling sound effects;
hence the term “5.1-channel” Dolby Digital.
In addition to the format features above, Dolby Digital
decoders offer downmixing for compatibility with mono,
stereo and Dolby Pro Logic audio from a number of bit
rates and channels. Another feature, called Dialog
Normalization, attenuates programs based on the
average level of dialog in a program relative to its peak
level (also known as Dialnorm) in order to achieve
uniform playback level.
Dolby Digital Surround EX
Dolby Digital Surround EX (the EX stands for EXtended)
is an extension of Dolby Digital encoding whereby a
surround back channel is matrixed into the surround left/
right channels for 6.1 channel playback. This allows for
compatibility with Dolby Digital 5.1 channel decoding, as
well as for decoding using Dolby Digital EX.
Dolby Pro Logic IIx and Dolby Surround
Dolby Pro Logic IIx is an improved version of the Dolby
Pro Logic II (and Dolby Pro Logic) decoding system. Using
the innovative “steering logic” circuit, this system
extracts surround sound from sources as follows:
• Dolby Pro Logic – 4.1 channel sound (mono
surround) from any stereo source
• Dolby Pro Logic II – 5.1 channel sound (stereo
surround) from any stereo source
• Dolby Pro Logic IIx – 6.1 or 7.1 channel sound
(stereo surround and surround back) from two
channel or 5.1 (and 6.1) channel sources
With two channel sources, the “.1” subwoofer channel is
generated by bass management in the receiver.
Dolby Surround is an encoding system which embeds
surround sound information within a stereo soundtrack,
which a Dolby Pro Logic decoder can then use for
enhanced surround listening with greater sound detail.
Dolby Digital Plus
Dolby Digital Plus is the next-generation audio
technology for all high-definition programming and
media. It combines the efficiency to meet future
broadcast demands with the power and flexibility to
realize the full audio potential expected in the upcoming
high-definition era. Built on Dolby Digital, the multi-
channel audio standard for DVD and HD broadcasts
worldwide, Dolby Digital Plus was designed for the next-
generation A/V receivers but remains fully compatible
with all current A/V receivers.
Dolby Digital Plus delivers multi-channel audio programs
of up to 7.1 channels (*) and supports multiple programs
in a single encoded bitstream with the maximum bit rate
potential of up to 6 Mbps and the maximum bit rate
performance of up to 3 Mbps on HD DVD and 1.7 Mbps
on Blu-ray Disc, and it outputs Dolby Digital bitstreams
for playback on existing Dolby Digital systems. Dolby
Digital Plus can accurately reproduce the sound
originally intended by directors and producers.
It also features multi-channel sound with discrete
channel output, interactive mixing and streaming
capability in advanced systems. Supported by High-
Definition Media Interface (HDMI), a single-cable digital
connection is possible for high-definition audio and
video.
Dolby TrueHD
Dolby TrueHD is the next-generation lossless encoding
technology developed for high-definition optical discs in
the upcoming era. Dolby TrueHD delivers tantalizing
sound that is bit-for-bit identical to the studio master,
unlocking the true high-definition entertainment
experience on high-definition optical discs in the next
generation. When coupled with high-definition video,
Dolby TrueHD offers an unprecedented home theater
experience with stunning sound and high-definition
picture.
It supports bit rates of up to 18 Mbps and records up to 8
full-range channels (*) individually with 24-bit/96 kHz
audio. It also features extensive metadata including
dialogue normalization and dynamic range control.
Supported by High-Definition Media Interface (HDMI), a
single-cable digital connection is possible for high-
definition audio and video.
HD DVD and Blu-ray Disc standards currently limit their
maximum number of audio channels to eight, whereas
Dolby Digital Plus and Dolby TrueHD support more than
eight audio channels.
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