Warner Brothers. "The Exorcist: The Sound of Silence." 1973, 2000. 10 May 2008 <http://theexorcist.warnerbros.com/cmp/silencebottom.html>.
This webpage offers the perspectives of many contributors to the soundtrack of The Exorcist. There are several instances of the unique mechanisms used to convey the unusual sound effects.
For example, Friedkin stresses the use of sonic contrast throughout the film. He wanted to use sound to match the extreme visual shifts onscreen, such as that between light versus dark. This creates a “startle effect”, where sound functions as a weapon that penetrates the audience with sudden assaultive effects, unpredictably followed by a surrounding quiet. Perfectly capturing this is the scene where the traumatizing noises of the x-ray machine suddenly disappear into thin air. The screen blacks out, making the moment much more intense.
In addition, many examples of diegetic sound exist throughout the film. In the opening scene, which displays countless workers digging in the rubble of the Iraqi desert, the sound of the axes hitting the rocks simultaneously occurs with the echoing sound that is produced. Apparently, Friedkin checked this scene over one hundred times in order to ensure its accuracy, in hopes of creating the most realistic soundspace possible.
Friedkin also perfected the voice of the demon. Initially, he tinkered with the combination of Blair’s voice and that of a male. However, the synthesized result sounded too fake. He resorted to calling an old friend—Mercedes McCambridge—in order to create a more convincing demonic tone. She went to great lengths to try and produce the most horrific noises; she chain smoked, swallowed raw eggs, and even tied herself to a chair, among other things. Eventually, her painful sounds were combined with frequencies of angry bees and slaughtered pigs to produce the relentless devil within Regan.
Overall, Buzz Knudson was responsible for bringing together all of these sounds and inserting them into a continuous flow. Hundreds of different sound experts were called in to contribute to even the smallest auditory effects. Artists would experiment with atonal beats using materials like crystal stemware, old leather wallets, and pencils. The track took over fifteen weeks to make, though most movies took around six weeks. Indeed, the film had brilliant sound engineering.
Part of the success of The Exorcist must be credited to the work of the sound production team. Sound functions as a storytelling element, becoming just as important as the visuals when it comes to horror filmmaking. Buzz Knudson pioneered the use of new ideas and technologies; he was able to blend in music with the background—never dominating a scene—yet subtly building up its intensity. His immense efforts were crucial in portraying the evil nature of the devil, certainly shocking audiences across the nation.