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Understanding Surround Sound
Today’s sophisticated surround sound systems seem to spawn a bewildering array
of technologies and acronyms. In this section, we will attempt to give you a basic
understanding of what all that jargon means. As a result, you will be better equipped to
take advantage of the best that home entertainment has to offer.
how many channels? Today’s surround systems are called upon to reproduce soundtracks that were designed
to include anything from one to seven separate channels of information. Some examples
might include:
• watching Casablanca
or The Wizard of Oz (both mono movies, having only a single
channel of audio information in the soundtrack)
• listening to a CD in stereo (only two channels of audio)
• watching the original Star Wars in the original Dolby Surround Pro Logic (four
channels of information derived from two channels)
• watching a modern movie, with a “5.1” soundtrack (meaning five different full-
range signals for the front and surround speakers, plus a special “.1” signal of
special Low Frequency Effects; for this reason, the “.1” channel is sometimes called
the “LFE channel.”)
Your new processor handles all these tasks with ease, switching to an appropriate
processing mode automatically upon sensing the nature of the incoming signal.
However, sometimes it may be up to you to select from among the various signals
available. For example, DVDs often contain multiple soundtracks, with varying
numbers of channels or even different languages. You must choose the one you would
like to hear, using the menu of the DVD itself. For that reason, it helps to have a better
understanding of the jargon that is likely to be presented to you in those menus.
We’ll cover the most common possibilities for you.
matrix or discrete? When movie makers first wanted to expand beyond simple stereo (left and right audio
channels only), they had a problem: the entire infrastructure on which they depended
was stereo.
A company named Dolby Laboratories saved the day by creating a system called Dolby
Surround that embedded two extra channels of sound in the existing stereo pair, in such
a way 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 decoding.
The disadvantage of matrix decoding is what you might expect – it is tough to
completely and perfectly separate two things that have been mixed together. Once you
have baked a cake, it is difficult to get back to the eggs and flour.