A Hum, and a Credit That Did Not Exist

For the first half-century of sound film, nobody was the author of a soundtrack. There were recordists, dubbing mixers, sound editors, effects editors, re-recording mixers: a chain of technical credits for a chain of technical services. Whatever the finished thing sounded like, it was not anybody's work in the sense that photography was somebody's work.

Apocalypse Now carried the credit sound designer, taken by Walter Murch, and it was the first film to do so. Murch is widely said to have pushed for the term precisely to make the point that post-production sound involves authorship, and the credit entered the industry permanently.

The job it describes is real, which is why the term survived. On a film of that kind somebody has to decide what the whole picture sounds like: when the war is close and when it is distant, when a room is dry and when it rings, when to replace realism with something subjective, when to drop everything out. Those are not servicing decisions.

Ben Burtt had done the equivalent on Star Wars two years earlier under a more conventional credit, and his working method is the clearest window into how invented sounds get made.

Take the lightsaber, which is the most recognisable fictional sound in cinema. Burtt had worked as a projectionist at university, and the booth's old projectors made a particular hum as they idled. Separately, with a microphone left running, he passed a television set and the microphone picked up its interference as a thin whine. Combined, those two recordings are the lightsaber's resting hum.

That is half the job. The other half is motion. A blade swung through the air changes pitch as it approaches and passes, so Burtt played the hum through a speaker and moved a microphone past it, capturing the Doppler shift directly rather than simulating it.

The principle generalises, and it is the thing to take from this lesson.

A sound invented from pure synthesis tends to be heard as artificial, because real mechanical sources carry small irregularities and harmonic messiness that the ear uses as evidence that something physical is present. So the reliable method is to find a real mechanism whose texture suits the imagined object, layer a second source to give it character, and then add a motion or interaction cue so it behaves like a thing in a space. A projector motor is not a plasma blade. It is, however, a real machine with the right kind of hum, which turns out to be what matters.

One more thing, in the spirit this subject keeps insisting on: be careful with the anecdotes.

The droid's name is the famous example. Lucas has described it coming from a label on a reel, reel two dialogue two, heard during a mixing session, and his accounts over the years name different films as the one being mixed, with a later archive find at Skywalker Ranch favouring American Graffiti over THX 1138. The lightsaber story has variant tellings as well, over whether the interfering television was in the booth or at home. The THX system's name, often assumed to be the film, is usually traced to the engineer Tomlinson Holman's initials with an X, and treated as a nod to the film as well.

None of this disturbs the craft. It is a reminder that in a field where the practitioners are charming and the stories get retold on stage for forty years, the method is better documented than the origin, and the method is the part you can use.