Film sound is carefully designed and plays an important role similar to visual elements. While some sound is recorded on set, most is added during post-production mixing to emphasize important sounds and set the atmosphere. Sound can be diegetic, existing within the film's world, or non-diegetic from outside the world, like soundtracks. It can also be synchronous matching the action, asynchronous separate from visuals, or contrapuntal juxtaposed for alternative meaning. Other elements include sound bridges, effects, and music to transition or link scenes, while silence is sometimes used to provoke audiences.