Films use a lot of diegetic and non – diegetic sounds.
Diegetic sound is sound that is visible on screen. Examples of diegetic sounds are:
voices of characters,
sounds made by objects in the story and
music coming from instruments.
Non – diegetic sound is sound whose source is neither visible on the screen or has been implied to be present in an action. Examples of non – diegetic sound are:
Sound added in to create a dramatic effect and
The distinction between diegetic or non-diegetic sound depends on our understanding of the conventions of film viewing and listening. We know of that certain sounds are represented as coming from the story world, while others are represented as coming from outside the space of the story events. A play with diegetic and non-diegetic conventions can be used to create ambiguity horror, or to surprise the audience comedy.