how many channels?
matrix or discrete?
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.
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
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.
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.
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