Documentaries employ several conventions to appear authentic and persuasive to audiences. The voiceover is usually presented as authoritative to influence viewers' opinions. Footage and events are portrayed as real, though voiceovers and editing can affect reality as seen. Using natural light and sounds during interviews enhances believability, as does archive footage. Experts are interviewed to authenticate views, though filmmakers can disprove dissenting opinions. Sound is either diegetic, from the scene, or non-diegetic, added for effect like music or narration.