Sound in film and TV must be carefully mixed to emphasize key sound elements, create particular atmospheres, and provide smooth transitions between scenes. Selective sound focuses on important audio, while ambient sound sets the setting. Diegetic sound has a visible source on screen, whereas non-diegetic sound does not and is not part of the film's world. Elements like voiceovers, theme music, and musical scores can develop characters and storylines or offer information, while silence is sometimes used to provoke audiences.