Audio
Fox officials were keen that the sound of their new wide-screen film format should be as impressive as the picture, and that meant it should include true stereophonic sound.
Previously stereo sound in the commercial cinema had always employed separate sound films, Walt Disney's 1940 release Fantasia had used a three-channel soundtrack played from separate optical film. Early post-war stereo systems used with Cinerama and some 3D films had used multichannel audio played from a separate magnetic film. Fox had initially intended to use 3 channel stereo from magnetic film for CinemaScope.
However, Hazard E. Reeves' sound company had devised a method of coating 35mm stock with magnetic stripes and designed a 3 channel (left, center, right) system based on three .063" (1.6mm) wide stripes, one on each edge of the film outside the perforations, and one between the picture and the perforations in approximately the position of a standard optical soundtrack. Later it was found possible to add a narrower .029" (0.74mm) stripe between the picture and perforations on the other side of the film; this fourth track was used for a surround channel, also sometimes known at the time as an "effects" channel. In order to avoid hiss on the surround/effects channel from distracting the audience the surround speakers were switched on by a 12 kHz tone recorded on the surround track only whilst wanted surround program material was present.
This 4-track magnetic sound system was also used for some non-CinemaScope films; for example Fantasia was re-released in 1956, 1963, and 1969 with the original Fantasound track transferred to 4-track magnetic.
Read more about this topic: CinemaScope