When you go to a movie theatre, producing perfectly synched sound that completely envelopes the room isn’t as simple as just playing an audio track. There are two forms of analog sound: optical process and magnetic.
In the early days of movies, many films used an optical process to create sound synched to the film.
In the optical process, a clear line is recorded into one side of a film strip, and the line’s width changes according to the film’s sound frequency. A light shines through this strip, and the light transforms into an electrical current thanks to a photocell. This current is sent to a pre-amplifier, which sends it to the amplifier, and then the signal goes to the speakers.
As filmmaking became more mainstream, the number of films that used magnetic recording as opposed to the optical process increased. Magnetic recording had better sound quality, but it is more expensive and degrades easily. The expense of the magnetic recording far outweighed the quality, leading to a significant problem for the film industry.
However, in the mid-1960s, Dolby sound laboratories created a method to reduce noise in the original optical process. The sound in the optical process due to this method was much cleaner – one example of its use is in A Clockwork Orange.
The first-ever movie with surround sound was Walt Disney’s Fantasia, which was released in 1941. It cost movie theaters a whopping $85,000 to install the special projectors and speakers that were needed to handle the four additional audio tracks. This system was installed in one theatre in Los Angeles and one in New York.
Soon, Dolby created a way to make surround sound more easily available with Dolby Stereo. Eventually, Dolby went on to create Dolby Digital for theaters, which debuted when Jurassic Park was released in the 1990s.
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