Most Of What An Audience Feels Arrives Through Sound

The picture tells you what is happening. The soundtrack tells you how to feel about it, and it does so without asking permission.

Try an experiment with any sequence: turn the sound off and watch it. The images survive, but the sense of scale, threat, warmth and space largely evaporates. Turn the picture off and listen instead, and a surprising amount of the emotional content is intact. Sound is processed faster than vision and with less conscious filtering, which is why it can be used to plant a feeling before a viewer has decided what they think. A room that hums slightly, at a frequency just above comfortable, will make an audience uneasy about a conversation that is, on paper, perfectly friendly. Nobody in the cinema will report hearing a hum.

A finished soundtrack is built from separable layers, and each layer answers a different question. Dialogue carries the literal information. Effects and foley establish physical reality: weight, texture, distance, whether a floor is timber or concrete. Atmosphere or ambience defines the size and character of the space and, crucially, defines what lies outside the frame. Music supplies the emotional frame and, more subtly, the tempo at which the audience is expected to process events. These layers are mixed against each other constantly, and the mix is where the film's priorities become audible. When all four fight for the same space, the result is loud and strangely uninvolving.

The most underrated layer is the one that describes off screen space. A picture shows a woman alone in a kitchen. Add the sound of traffic and she is in a city, connected, findable. Add distant wind and no traffic at all and she is remote, and the isolation becomes a fact about her situation rather than an interpretation. Add a floorboard from the next room and the entire scene changes genre. None of this required a single extra frame of photography, which is why sound is where a modest production can achieve effects that would otherwise cost a fortune, and why it is so often the last department given time.