Diegesis, Mimesis, and Sound

There are two types of styles when it comes to filmmaking: diegesis and mimesis. Diegesis is the act of telling the story, whereas mimesis is actually showing the story. In short, it is basically storytelling versus miming. For example, reality television is considered diegesis over mimesis because the story is being told, not shown. Film, however, is more about mimesis and showing the story to viewers. 

Sound, voice, and music are very important components to most movie and television viewing experiences. Sound is there to enhance the scenes of a movie, and it can be an indicator of a mood change or help establish tone. Diegetic sound is noises and music on-screen that the character in the story is aware of and can hear, and non-diegetic sound is something only the audience can hear outside of the story. An example of non-diegetic sound, or sound that doesn't take place in the "world" of the movie, would be a narrator's commentary, or mood music. This comes from off-screen, or somewhere outside of the story. Diegetic sound would be the character's voices, or music coming from instruments being played inside of the movie/story. Sound effects can be both diegetic and non-diegetic, as well as music. 

Three important rules for sound editing is to make sure you have room tone in your scene and use it to your advantage, to keep your dialogue/narration and music separate from one another, and to mix your audio levels until you think they sound good in relation to one another.