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How Surround Sound Works

        Tech | Speakers

What is Surround Sound?
Sony home-theater system, featuring a DVD player with built-in surround-sound receiver and a collection of speakers
Sony home-theater system, featuring a DVD player with built-in surround-sound receiver and a collection of speakers
Photo courtesy Sony

There are many ways to make and present a sound recording. The simplest method, and the one used in the earliest sound movies, is called monaural or simply mono. Mono means that all the sound is recorded onto one audio track or channel (a single spiraled groove in a record, for example, or a single magnetic track on tape), which is typically played on one speaker.

­ Two-channel recordings, in which sound is played on speakers on either side of the listener, are often referred to as stereo. This isn't entirely accurate, as stereo (or stereophonic) actual refers to a wider range of multi-channel recordings. Two-channel sound is the standard format for home stereo receivers, television and FM radio broadcasts. The simplest two-channel recordings, known as binaural recordings, are produced with two microphones set up at a live event (a concert for example) to take the place of a human's two ears. When you listen to these two channels on separate speakers, it recreates the experience of being present at the event.

Surround recordings take this idea a step further, adding more audio channels so sound comes from three or more directions. While the term "surround sound" technically refers to specific multi-channel systems designed by Dolby Laboratories, it is more commonly used as a generic term for theater and home theater multi-channel sound systems. In this article, we'll use it in this generic sense.

There are special microphones that will record surround sound (by picking up sound in three or more directions), but this is not the standard way to produce a surround soundtrack. Almost all movie surround soundtracks are created in a mixing studio. Sound editors and mixers take a number of different audio recordings -- dialogue recorded on the movie set, sound effects recorded in a dubbing studio or created on a computer, a musical score -- and decide which audio channel or channels to put them on.

In the next section, we'll learn a little bit about how surround sound was created and see how it was configured in older theaters.

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