Dolby Surround

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Dolby Surround was the earliest consumer version of Dolby's multichannel analog film sound format Dolby Analog SR (Spectral Recording).

When a Dolby Surround soundtrack is produced, four channels of audio information—Left, Center, Right, and Mono surround—are matrix-encoded onto two audio tracks. The stereo information is then carried on stereo sources such as videotapes, laserdiscs and TV Broadcasts from which the surround information can be decoded by a processor to recreate the original four-channel surround sound. Without the decoder, the information plays in standard Stereo. The Dolby Surround decoding technology was updated during the 1980s and re-named Dolby Pro Logic. The term Dolby Surround is still used, however, to describe soundtracks that are matrix-encoded using this technique.de:Dolby Surround