Macro of 35mm film audio tracks, from left to right: Sony SDDS, Dolby Digital, analog Optical, and finally DTS time code.

Two methods of recording sound onto film. Variable density (left) and Variable width (right).

 Graphic of a 35mm video film depicting two frames of SMPTE color bars defaced with a caption reading “TELECAST”. A Variable Density audio track is present. It contains a 400Hz sine wave spanning 2/24 of a second. The source audio used to generate this image has a sample rate of 11520Hz.