Non-diegetic sound
Sound the characters can't hear. The audio code's licence to address the audience directly.
- audio
- film-language
A sub-concept of the Audio code. Diegetic sound belongs to the story world; non-diegetic sound belongs to the telling. Score is the obvious case, and because characters can't hear it, it is the one channel on which the filmmaker speaks to the audience with no narrative alibi at all.
Canonical case
Bernard Herrmann's strings-only score for Psycho (1960) — what Herrmann called a "black-and-white sound" for a black-and-white film — and above all the shrieking glissandi of Psycho — the shower scene. The production story is its own note: Herrmann scored the shower against orders.
Teaching angle
Play the shower scene silent, then scored. The images are identical; the violence roughly doubles. That gap is the non-diegetic channel, measured.
Sources
Bordwell & Thompson — Film Art for the diegetic/non-diegetic distinction and its edge cases; Rebello for the scoring history.