Diegetic sounds originate from within the scene and can be heard by the characters, while non-diegetic sounds are added in post-production and can only be heard by the audience. Sound is important to drama because it helps viewers understand the plot and suggests what is happening, even without visuals. Different genres of TV drama call for specific types of non-diegetic music, such as hospital dramas using somber music or police dramas employing suspenseful music.