The next wave of home theater sound innovation came with the launch of digital
distribution formats, including DVD, digital cable, DIRECTV digital satellite
broadcasting and free, over-the-air digital television broadcasting. These digital media
opened the door to digital surround sound. Dolby Laboratories answered with the Dolby
Digital system. Compared to Dolby Pro Logic decoding, the Dolby Digital system has
Digital sound quality. The movie sound tracks now approach the sound quality of
Compact Disc. You'll hear full frequency response, low noise and exceptional clarity.
Discrete channels. Where the Dolby Pro Logic decoder must pull the four channels
out of two stereo signals, the Dolby Digital system keeps every channel separate, or
More channels. Where the Dolby Pro Logic system has a single Surround channel,
the Dolby Digital system delivers a separate channel to the Surround-Left and
Surround-Right speakers. All told, there are 5.1 separate channels. That's five full-
range channels (Left, Center, Right, Surround-Left and Surround-Right), plus a Low
Frequency Effects channel to drive the subwoofer.
Low-Frequency Effects (LFE) channel. The human ear can't detect where low-
frequency bass is coming from. This "omnidirectional" quality of bass means that a
single subwoofer can provide bass for an entire surround sound system. The
subwoofer bass will blend with the full-range speakers for a dynamic, high-impact
soundstage. The LFE channel is often called the "0.1" channel because the
subwoofer handles roughly one-tenth the frequency range of the full-range channels.
Scalability. While the Dolby Digital system is often called a 5.1-channel system, it
can also support fewer channels, all the way down to mono, for movies and TV
shows produced before the 1970s.
Since the acceptance of Dolby Digital encoding, the number of surround sound
formats has continued to grow. But don't worry. Modern A/V receivers are good at
automatically detecting the surround sound format and automatically applying the best
Dolby Digital® surround sound. This is the surround sound system used on most
DVDs, on DIRECTV satellite broadcasts and on free, over-the-air High Definition
TV broadcasts. You need a receiver with Dolby Digital decoding.
Dolby Digital EX 6.1-channel sound. The new encoding format includes a matrix
"Surround Back" channel.
Dolby Pro Logic surround sound. This decoding is important because it works
with the Dolby Stereo signals encoded into literally thousands of movies and a large
The Sony Guide to Home Theater
Surround Sound Formats