 Four channels of information (Left, Center, Right and Surround) were matrix-encoded into two optical soundtracks on 35 mm theatrical release prints, occupying the same area of the film which previously held the monophonic soundtrack.The matrix-encoded track was decoded by the cinema processor in the theater during exhibition.Ultra Stereo Labs (USL), which had been concentrating on the manufacture of sound equipment for studio screening rooms, was drawn into the exhibition-end of the business.