What is non-diegetic sound?

Non-diegetic sound refers to audio that exists outside of the narrative world of the film. This means it is not heard by the characters themselves, which allows it to serve a specific purpose in enhancing the storytelling experience for the audience. A prime example of this is a musical score, which can evoke emotions, build tension, or underscore key moments in the film without the characters being aware of its presence.

In contrast, sounds made by characters, such as dialogue or sounds they produce, fall within the diegetic realm, as do environmental sounds like background noise or ambient sounds that characters would realistically hear. Non-diegetic sound enhances the viewing experience by influencing audience perceptions and emotions without being directly related to the on-screen action or the characters' experiences.