Meaning of optical soundtrack

op'tical sound'track

Pronunciation: [key]
  1. the final soundtrack on a motion picture, which appears as a band of black and white serrations along a strip of film to the left of the composite print. Light is shined through the serrations and is converted to audible sound. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.