Dolby (Surround)
Dolby Surround was the earliest consumer version of Dolby's multi channel analog film sound decoding format Dolby Stereo, introduced to the public in 1982. The system has four channels of audio information - left, centre, right, and mono surround – which are matrix-encoded onto two audio tracks. The stereo information is then carried on stereo sources such as videotapes, laserdiscs and television broadcasts from which the surround information can be decoded by a processor to recreate the original four-channel surround sound.