Think of the films you love most from the late 70s through the early 90s. Raging Bull, The Last Waltz, Planes, Trains & Automobiles, The Princess Bride, Stop Making Sense, The Terminator, Goodfellas. There’s a good chance that you may never hear the original soundtrack again.
For 50 years after the talkie revolution, the optical, mono, analog soundtrack was ubiquitous on 35mm prints around the world. There were alternatives–primarily four-track magnetic stereo. But that more than doubled the cost of making prints, so optical mono remained the standard.
All that changed in the late 1970s,
when after Dolby introduced an optical stereo format for 35mm prints. It didn’t sound as good as four-track magnetic, but it was a whole lot cheaper. The 35mm version of Dolby Stereo (Dolby used the same name for an entirely different format in 70mm) made multitrack audio ubiquitous in movie theaters for the first time. [12/10: I altered this paragraph because my original version implied that Dolby introduced this technology in the late 1970s. It was introduced in 1976.]
Dolby used three technologies to improve the then 50-year-old mono optical soundtrack. First, they split it in two, turning it into discrete, two-track stereo. Then they added a noise reduction filter. Finally, they used some electronic wizardry to channel the two tracks into four different directions. The technology could decode properly-mixed left and right tracks into left, center, right, and surround channels.
By 1978, Dolby Stereo was the norm for action movies, sci-fi, fantasy, concert movies, and musicals. By 1985, almost every Hollywood movie used the format. By 1990, independent and foreign films used it, as well. The big blockbusters, of course, were released in 70mm, with the far superior, magnetic, six-track Dolby Stereo. But the 35mm prints of the same movies used the optical, two-track, four-channel version.
The rise of Dolby Stereo in movie theaters corresponded with the rise of stereo television, first with Laserdiscs, HI-FI VCRs, and finally stereo broadcasting. As it happened, a Dolby Stereo mix worked reasonably well as standard two-track stereo. It didn’t really need the decoder
But it sure sounded better with it. In 1982, Dolby licensed the channeling technology to home audio receiver manufacturers, under the brand name Dolby Surround. The decoding technology is media-agnostic; as long as the media carried two-track stereo, the right receiver, with the Surround feature turned on, could convert it to four-channel surround. To my mind, this was really the beginning of home theater.
Digital 5.1 audio came to movie theaters in the early-to-mid 1990s. But all of the successful digital formats steered clear of interfering with the analog Dolby Stereo soundtrack, needed for backward compatibility and as a backup. Thus, although seldom heard, Dolby Stereo remained on almost all prints until the studios stopped making prints.
When digital 5.1 sound came to home media with DVDs, it was renamed Dolby Surround 2.0, to differentiate it from 5.1 sound. It was pretty common in the early days of DVDs, but soon disappeared. Today, it’s almost impossible to find a Dolby Surround 2.0 mix on any Blu-ray disc. The movies from the glory days of Dolby Stereo are almost always remixed to 5.1 (or 7.1), without even supplying the original mix we heard when we fell in love with them.
I understand that many people, including the filmmakers, prefer the newer, fancier mixes. But I do wish they would include the originals.