Perspecta
Perspecta is a sound recording process that was used for many motion pictures between 1954 and 1957 , including most of the films made in Vistavision .
This process is a kind of “ stereo replacement ”. The sound track contains an optical mono recording, which is compatible with the method used up to that point, and three additional control tones in the range below 80 Hz. Playback takes place on three loudspeakers near the screen (i.e. not distributed in the auditorium) and the control tones control the distribution of the Signal to the three loudspeakers.
The process was mainly used by MGM , Paramount Pictures and Time Warner .