This document discusses different classifications and uses of sound in films. It describes sound as being classified into sound effects, music, and spoken language. Sound can be synchronous, recorded at the same time as images, or nonsynchronous, recorded later and dubbed onto images. Sound can also be diegetic, coming from within the depicted scene, or nondiegetic, coming from outside the scene, like voiceovers or background music. The document then provides examples to illustrate synchronous/nonsynchronous and diegetic/nondiegetic sound. It continues discussing the history of sound in films and different uses of music to set mood, suggest locales or characters, or control emotional shifts.