Sound Printing

Optical sound tracks, whether variable area or variable density, are always printed on a continuous contact rotary printing gate, even if the image is printed by step contact. Even early rotary contact printers of the 1930's had a separate sound head to allow the sound to be printed after the image, so that the entire combined print could be printed in one pass.

Older optical and step contact printers rarely had an inline continuous head to print the sound until the 1960's, and a print made on one of these printers had the sound printed by a second pass through a special sound printer [or a normal rotary contact printer with a sound head].