30
Understanding Surround Sound
Today’s sophisticated surround sound systems have spawned a bewildering
array of technologies and acronyms. In this section, we’ll give you a basic
understanding of what all that jargon means. As a result, you’ll be better
equipped to take advantage of the best that home entertainment has to offer.
how many channels?
Today’s home entertainment systems reproduce soundtracks that include
anything from one to eight separate channels of information. Examples include:
• Watching mono movies, such as
Casablanca
or
The Wizard of
Oz
, having only a single channel of audio information in the
soundtrack.
• Listening to a musical CD, which is typically stereo or 2-channel
sound.
• Watching the original
Star Wars
in the original Dolby Surround
Pro Logic format, which is four channels of information derived
from two channels.
• Watching a recent movie or T.V. show in a 5.1-channel or
7.1-channel surround format, which identifies that the source
material has either five or seven full-range signals for the front,
surround, and rear speakers plus the .1 signal for the Low
Frequency Effects (LFE), also referred to as the LFE channel, for
the subwoofer.
Your SSP handles all of these tasks with ease, switching to an appropriate
processing mode automatically upon sensing the nature of the incoming signal.
However, you may still have to select from the available choices. For example,
disc-based media often contains multiple soundtracks with varying numbers of
channels and even different languages. Because you may have to choose the one
you want to hear using the menu of the media itself, you should know what
jargon you’ll likely see.
matrix or discrete?
When movie-makers first wanted to expand beyond simple stereo (left and right
audio channels), they had a problem - the entire infrastructure on which they
depended was stereo.
Dolby Laboratories solved that problem with a system called Dolby
®
Surround
that embedded two extra channels of audio sound into the existing stereo pair
so that specialized circuitry could retrieve the extra information with reasonable
accuracy. This technique, whereby channels are mixed together with the
intention of separating them later, is called matrix encoding and decoding.
The disadvantage, as you might expect, is that it is difficult to completely and
perfectly separate two channels that have been mixed together.
By contrast, modern soundtracks use discrete channels of information. That is,
each speaker has a distinct signal that is completely independent of every other
channel. This approach is clearly more desirable, since it gives the movie-makers
more creative control over the quality of your experience. Musicians also prefer
discrete formats, since it allows them to place their instruments and voices with
greater precision, to create the musical effects they desire.
