Film sound is carefully designed and added during post-production to emphasize important elements and set the atmosphere. There are two main types of sound: diegetic, which exists within the world of the film, and non-diegetic, which comes from outside the film like music or enhanced effects. Sound can also be synchronous to match actions, asynchronous to come from outside the story, or contrapuntal to create a different meaning by clashing with the visuals. Other sound elements include voiceovers, theme music, musical scores, and strategic use of silence.