Music that originates within the film's world — orchestra on stage, radio in the car, live band in the club. Audience hears what characters hear.
You're sitting in color grading, and the editor plays you the scene: A detective enters a jazz club, the music swells. That's not the composer's score – that's the band on stage within the film itself. The detective hears it, we hear it with him. We call this diegetic music, and it's one of the strongest tools for drawing viewers into the cinematic reality.
The crucial difference from film score lies in spatial logic: Diegetic music exists within the diegesis – that is, in the world the camera shows. A clock ticking in the living room? That's diegetic music. A music video playing on the TV? Diegetic music. A song coming from invisible speakers while a character works in the kitchen? That too. The characters can notice the music, comment on it, turn it off. On set, this concretely means you need playback. The actor dances or sings to the music – and this music will be precisely synchronized later. In the edit, the editor controls every beat, every phrase, until the lip-sync is perfect. Not a second of tolerance.
In practice, you need a different approach for diegetic music than for score. It needs to be spatially plausible – if the band is playing three meters away, it sounds closer than if they're on the other side of the hall. The sound designer works with frequency cuts, reverb, and volume ratios to create this spatial depth. A scene in a concert film? Here, diegetic music becomes a narrative anchor point – it can build tension, it can control emotions without feeling artificial. A wedding scene with a live band tells us more about the characters through the music choice than any dialogue exposition could.
The most common mistake: mixing diegetic music too loud, as if it were film score. No – it competes with dialogue, ambient sound, and other effects. It needs to feel natural, even if it's technically precise. Sometimes, diegetic music is deliberately dimmed when important action is happening in the foreground – the viewer should perceive the music without it dominating. This is high-level balancing work.