What the audience hear, including dialogue, music and sound effects which helps create atmosphere.
Diegetic sound comes from within the world of the story, it’s sound that the characters can hear. If you can see the source of the sound or know it exists in the scene, it’s diegetic. Examples include dialogue, footsteps, phones ringing, cars passing, or music playing from a radio on screen. Diegetic sound helps make the scene feel realistic and grounded in its world, and it can also tell us important things about what’s happening.
Non-diegetic sound is added in post-production and is not part of the story world, meaning the characters do not hear it. This includes background music, narration (voiceover), and dramatic sound cues used to create emotion or build tension. For example, suspenseful music might play while a character walks into a dark room, even though there's no music actually playing in the scene. Non-diegetic sound is a way for creators to influence how the audience feels and to highlight important moments in the story.
Sound effects are sounds used to match the action or atmosphere in a scene. These can be realistic, like the sound of a door creaking, or exaggerated for effect, like a cartoon "boing" when a character jumps. While many sound effects represent diegetic sounds (because the character would hear them), they’re often added or improved during editing. In interactive media like games or apps, sound effects can be triggered by the user's actions, like a reward sound when a level is completed.
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