What differentiates diegetic sound from non-diegetic sound?

Diegetic sound refers to audio elements that are part of the narrative world of the film or media. This type of sound can be heard by the characters within that world, making it an integral part of the storytelling. Examples include dialogue spoken by characters, sounds made by objects in the scene, and background noise existing within the environment.

In contrast, non-diegetic sound is not heard by the characters and is intended solely for the audience. This includes elements like a film's score, narration that provides commentary or context, and sound effects that are added for dramatic effect but do not originate from the scene itself.

Therefore, the distinction lies in the characters' awareness of the sound: diegetic sound is part of their experience, while non-diegetic sound serves to enhance the audience’s understanding or emotional response to the story.