, is the SDDS soundtrack as an image of a digital signal. Between the perforations is the Dolby Digital soundtrack (note the tiny Dolby “Double D” logo in the center of each area. ) To the right of this is the stereophonic analogue soundtrack, optically recorded as waveforms containing the audio signals for the left and right audio channels. In the centre is the anamorphic picture. ]] 35 mm film is the film gauge most commonly used for chemical still photography and motion pictures.