Which of the following is an example of non-diegetic sound?

• A. The film's musical score heard by the audience but not in the story world.
• B. Dialogue between characters.
• C. Footsteps of a character, heard by characters on screen.
• D. A radio playing in the scene that characters can hear.

Answer: (A)

Non-diegetic sound is sound that the audience hears but the characters in the story do not hear. It is external to the story world and is used to shape mood or provide commentary. In this context, the film’s musical score heard by the audience but not in the story world fits that idea perfectly, because the characters wouldn’t be aware of it as part of their environment. By contrast, dialogue, footsteps, and a radio playing within the scene are all sounds that exist in the characters’ world, so they are diegetic.