Tension and the Range of Extension
I recently did some work exploring a property of atmospheric or ambient sounds in film identified by Chion as the range of extension (Chion 1994). Extension refers to the breadth of the offscreen environment represented in the soundtrack, which can range from Vast, as heard in Bladerunner and Rear Window, where all the sounds of their respective cities can be heard, to Null, as used in Red Road where only the close personal foley of the onscreen characters is heard, nothing of surrounding environments.
I was interested in using the range of extension as a means by which to evoke tension in a scene, so I created 3 new soundtracks for a scene in Predator where the soldiers are wading through the jungle, before they encounter the Predator for the first time. Their scout senses possible danger ahead and the squad comes to a halt. There are a few silent moments as the soldiers wait while the scout tries to evaluate the danger, before he dismisses it as "probably nothing" and moves on.
The video below shows the first version, which has a null extension.
In this version I added only the personal foley sounds for the characters seen in the camera frame, including footsteps, brushing through foliage, rustles of clothing and some soft metallic sounds from their weapons. I found this version of the soundtrack was quite effective at evoking tension. The null extension draws the audience close in amongst the characters, and the near silence highlights the scout's strain to see or hear what might be lying in wait ahead of them. However, the scene is perhaps too long to maintain this approach throughout, as the minimal amount of sound could lead to disinterest at points, despite the established tension.
The next video shows a version of the scene with a vast extension.
I took the null version and added several layers of ambience to suggest the wider jungle environment. I began with some library recordings of rainforest ambiences, and built up layers of animal and bird sounds. My intention was to create tension by using the soundtrack to give an oppressive, smothering feel to the jungle, so I added layers of sound that had a more constant, noise-like characteristic such as insect noise, wind and running water.
Again however, I felt that the scene was too long to adopt this approach throughout. Thought it does help give oppressive feeling I was trying to achieve, the constant nature of the background sounds tends to even out the overall dynamics of the soundtrack, thereby diminishing its impact.
The next video shows a version which varies the extension of the soundtrack.
In this version the extension starts vast, establishing the oppressive feeling of the jungle. After the first cut to the predator point-of-view, the extension begins to narrow down to near-null at the peak point of tension in the scene, and is restored to vast at the final cut where the tension is released. I used the cuts to the Predator POV to disguise the removal of ambience layers and drops in the ambience volume. I also made use of points where the audience are focused on foreground sounds, such as footsteps or dialogue to apply subtle fades to further reduce the ambience.
This version is quite effective at both building and releasing tension and maintaining an interesting dynamic over the course of the scene, and gives support to Chion's position that variation in the range of extension within scene can be a useful cinematic tool.
References
Chion, M., 1994. Audio-Vision: Sound on Screen. New York: Columbia University Press.
Predator is copyright of Twentieth Century Fox Film Corporation