The 1970s: Dolby Stereo
True surround sound made a comeback in the 1970s with the introduction of
Dolby Stereo. In spite of its name, this was an optical four-channel technology, introduced in 1976 by
Dolby Laboratories.
Instead of using magnetic audio tracks, which tended to be of lower fidelity, Dolby reverted back to the earlier—and superior—optical recording technology. It also added noise-reduction technology for clearer playback.
The big boost for surround sound was the release of a single movie—1977's
Star Wars, with its swooping rear-channel effects. The success of
Star Wars inspired theater owners to upgrade their sound equipment to the Dolby Stereo standard, and led to other producers and studios embracing the surround sound format.