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Revised March 12, 2024

Surround sound in movie theaters has been around much longer than most people realize. Many movies, beginning in the 1950s with CinemaScope® films, used several tracks of audio on the film to give the sense of being surrounded by sound. These movies had discrete (separate) tracks for each of several speakers behind the screen, and one for an array of speakers to the sides and behind the audience, surrounding them in sound.

Surround sound lets the movie makers “recreate” the sound of the spaces and events they are portraying on screen. By putting into the surround speakers the sound of chirping birds, wind whistling through trees, or a helicopter coming from behind on the right towards the front on the left, the atmosphere is more realistic and believable, immersing us further into the movie.

In addition, having several separate channels of sound behind the screen lets the movie maker provide a much more convincing sonic image up front since the sound of a car whizzing across the screen can move with the image of that car.

Back then, multiple channels of sound were only possible by putting magnetic sound tracks (like there are on magnetic recording tape) to the left side of the picture frame on the big 70mm film prints. Because these prints were expensive, economies of scale drove them out of the mainstream by the late 60s. Surround sound was only available on the biggest budget films and even then, only in big “first run” 70mm-capable theaters in major cities.

In 1977, Star Wars brought us not only a new genre of science fiction film, but a new sound format that would impact motion pictures like no other. Dolby created a way to deliver four channel soundtracks optically on ubiquitous 35mm film. Through their experience with noise reduction technology, Dolby was able to put two optical audio channels on the film in the space previously occupied by the Academy Optical Mono track. They embedded a center and surround channel into these left and right optical tracks. This is called a “Matrix”. When decoded in the theater, the system yielded three screen channels and one surround. The thrill of multiple screen channels and surround sound was now available for all movies at reasonable production costs. By the mid 80s, virtually every commercial movie release featured four-channel Dolby Stereo® sound.

In 1992, with the release of Batman Returns, Dolby unveiled the next generation of motion picture sound, Dolby Digital® (a.k.a. Dolby Stereo SR-D). Dolby Digital (DD) featured three front screen channels, two surround channels, and one LFE (Low Frequency Effect) track. The sound is stored on the film in digital form, and all channels are discrete, meaning that each channel is a distinct or separate track in the recording, rather than the rear channel and front center channel having to be extracted from two stereo channels like it is with Dolby Stereo®.

Dolby Surround 7.1® is a surround sound system introduced by Dolby Laboratories on March 16, 2010 at ShoWest 2010. It is the successor and an extension to Dolby Digital and its EX counterpart. For the first time, true 7.1 capabilities have been implemented into the cinematic space by adding two discrete back surround channels into the mix, replacing the old matrixing strategy of Surround EX. Unlike EX, however; Dolby Surround 7.1 is the first digital cinema-exclusive audio technology, so owners of traditional 35mm projection systems were unable to take advantage of the new system (as the decoders only outputted digital audio from that sound system).

Despite a great deal of hype from Dolby from that time, the technology ultimately proved to be short-lived as the technical prowess of Dolby Surround 7.1 was quickly overshadowed by Dolby Atmos two years later in 2012, allowing for far more than 7.1 channels with its spacial encoding.

Releases featuring only Dolby Surround 7.1 soundtracks would be phased out soon after, and no films after 2014 would be released with a Dolby Surround 7.1 soundtrack as its highest-end format. However, it would be used as a fallback soundtrack for Atmos films for non-spacial-compatible auditoriums.  https://dolby.fandom.com/wiki/Dolby_Surround_7.1#:~:text=Dolby%20Surround%207.1%20is%20a,Digital%20and%20its%20EX%20counterpart.

There are alternatives to Dolby surround sound, with DTS being the main competitor. DTS:X® is the equivalent to Dolby Astmos®. Commercial movie theaters can have dozens of surround sound channels, but in general, the versions of those movies that we watch in our home theaters are much more limited with between 7 and 11 channels. However, our home theater processors can generate sound in channels that are not encoded in the movie Blu-ray discs or streamed movies.

Today, just about every commercial movie release features surround sound in one format or another.