When someone asks “What does sound do in a movie” most of us are at least a little confused about how to answer that question. Obviously both music and sound effects can make you feel a certain way. Sound effects can clearly add realism to a scene; make it more exciting, more mysterious, or funny. Same for music. But beyond those obvious jobs, it can be hard to specifically say what sound is doing.

Here are some of sounds jobs. Very often a given sound will be doing two or more of these at the same time:
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- suggest a mood, evoke a feeling
- set or modify a pace
- indicate a geographical locale
- indicate a historical period
- indicate changes in time
- connect otherwise unconnected ideas, characters, places, images, or moments
- define a character
- clarify the plot
- heighten realism or diminish it
- heighten ambiguity or diminish it
- draw attention to a detail, or away from it
- smooth otherwise abrupt changes between shots or scenes
- emphasize a transition for dramatic effect
- describe an acoustic space
- startle or soothe
- exaggerate action or mediate it
- indicate the geography within a scene*

If two different sounds are competing while trying to accomplish any one of these jobs, that can be a red flag, because unless they are orchestrated well together, there’s a good chance that each is undercutting the impact of the other rather than each amplifying the other.

This often happens when music and sound effects are attempting to make essentially the same statement at the same time. One of the most difficult aspects of sound mixing is finding ways to feature one sound or set of sounds in each moment and shifting that focus so that the audience feels they are hearing everything they are supposed to be hearing.

​Simply playing every sound loud is usually a disaster unless the goal is to create a wall of noise, which sometimes it is.