A digital audio encoding system from Dolby that was first used in movie theaters in the mid-1970s. It recorded four channels of audio and provided a breakthrough re-introduction of the optical soundtrack over magnetic tracks on 35mm film. Many noise reduction and equalization techniques were also used on 70mm magnetic-recorded film. Dolby Stereo was later renamed the Dolby analog format. See
Dolby Surround and
Dolby Digital.