Ambience

Ambience (or atmosphere, 'atmos') is the background sound layer that establishes the acoustic environment of a scene — the room tone of an interior, the wind and distant traffic of an exterior, the crowd murmur of a restaurant, the air handling of an office. Ambience is recorded as wild track sound (audio captured separately from picture, without dialogue, usually 30 seconds to several minutes per location) by the production sound mixer at every location. It serves multiple functions in post: it fills the gaps between dialogue lines (a cut from one shot to another would feel jarring if it transitioned from ambient sound to silence), it creates continuity (the same ambience layered under different shots in the same location ties them together), and it carries narrative tone (an isolated, sparse ambience reads as tension, a busy layered ambience reads as energy). Sound designers typically build ambience as multi-layered beds: a base layer (room tone or distant traffic), a midground layer (closer specifics like AC units or birds), and a foreground layer (distinct identifiable sounds that establish location specifically). Stock libraries (Sound Ideas, Pro Sound Effects, BBC Sound Effects Library) provide ambience options, but original recordings from the actual location are preferred when available. Ambience is mixed at lower levels than dialogue (typically -30 to -40 dBFS in a feature film mix) but is crucial to spatial believability. Reference: Sonnenschein, 'Sound Design.'