Orson Welles' 1941 masterpiece Citizen Kane was hailed for its innovative use of film technique – some new, some appropriated, all made fresh by Welles' stylistic panache. Welles used deep focus photography, matte paintings, sets with ceilings, fake newsreels, dissolves to mask cuts. Especially inventive was Welles' sound design. His radio background in the Mercury Theater gave him a large bag of tricks to draw from in creating the soundtrack for his first film.
Sound Design as Illusion
Welles' most basic use of sound was to create the illusion of offscreen elements, to make the viewer "see" what is not actually onscreen. This is most striking in the rally scene, when gubernatorial candidate Kane is giving a speech in a huge, packed hall. The speech is loaded with lines that draw thunderous applause. In reality, of course, there is no huge hall, no clapping crowds, just a few matte paintings and the sounds of applause, just as outside the building after the rally we hear a marching band without seeing one. (A large reason for these illusions was financial – Citizen Kane did not have a big budget, so why pay for extras when noise can be substituted cheaply?)
Sound Design as Suggestion
A more imaginative use of sound was to add depth and power to a scene, to evoke feelings in a suggestive, almost subliminal way. This is most evident in the scenes inside Xanadu, Kane's vast "pleasure dome." When Kane and his wife Susan speak to each other, their voices boom. One is tempted to say they echo, but there is no echo. There should be, given the size of the space they occupy, but Welles chooses to just enlarge the sound, giving it a spooky, otherworldly quality, as if Xanadu was not just a palace but another planet. Something similar happens when the reporter Thompson is speaking to the butler Raymond: here the voices have the sound of people speaking in a sepulcher.
Sound Design as Emotion
Yet a third use of sound is to convey the emotional state of a character beneath the surface action. The most glaring example comes just before the enraged Kane destroys Susan's room after she leaves him: we see a cockatoo flap its wings and screech, the noise a substitute for the screaming of Kane's wounded ego. A more subtle instance comes when Kane and Susan are arguing in their tent and Kane slaps her. We hear, in the deep background, a woman screaming, as if being attacked. Likewise, after Susan attempts suicide, we see her in bed explaining to her husband what drove her. On the soundtrack are faint echoes of the opera singing that made her a laughingstock.