From an egg boiling to a planet exploding, how movie sound effects are made

Photo by Rod Long on Unsplash

If you’re a film fanatic or interested in sound design, we’re sure you find the world of movie sound effects (FX) as spellbinding as we do. For those who don’t know anything about how movie soundtracks and audio are created, we’ve put together a brief introduction.

Setting the Stage

There are a number of different people who work on the soundtracks to film. There are those who score the music, sync dialogue and those who produce the sound FX noises and provide ambient sounds which add audible interest to a movie.

These audible accents could be the sound of a tent flapping in the wind or a slap to the face, literally anything from an egg boiling to a planet exploding.

When a movie is filmed, the sound that is captured on set is mostly just the actor's dialogue. Most other sounds, even footsteps, are recorded later in a specially designed sound stage. These places are called Foley stages or Foley studios, and the sound FX artists are called Foley Artists.

Jack Foley and Foley Artists

The Foley process takes its name from Jack Foley who, in the early days of film, was the developer of many of the techniques that are still in use today. Much of the sound performance is performed along with the projected film for dynamic and realistic effect.

Footsteps, for instance, must be perfectly timed to give the illusion that they are occurring at the exact moment they are on the screen. It is even integral to the realism of the soundtrack that the Foley artist wears the correct shoes to match the on-screen actor.

For example, take Thor in the Avengers movies. A character like that needs heavy substantial footsteps. This would not be the same as say Elsa in the Frozen movies. Thor’s hefty footsteps might be a hilarious addition to the dainty Elsa, but not exactly believable.

The best sound FX tracks are those that enhance the audible experience of the movie and sound as natural as possible. Foley tracks should emphasize the action but not be noticed. These are the sound FX that really feel real.

Field recording

Other things such as car engines, explosions and gunshots, which would be difficult or dangerous to record in an enclosed studio environment, are often recorded on location. This could be on the film set as the action takes place or at a specialized site, such as a firing range or race track.

This on-site recording is known as field recording. Often a realistic sound can be produced by something other than the item on screen.

Why do we need Foley FX

Aside from the obvious, that explosions, footsteps and swooshing lightsabers make a movie more exciting, dynamic and add impact to a scene, without Foley FX movies are just too quiet. Sound is an integral part of the human experience and can be just as stimulating as vision.

Imagine a scene where a person is standing on a frozen lake. Without any sound except for a dialogue, this scene would not feel natural. There are many possible sounds that can be added to make the scene more immersive for the viewer.

There may be snow on the ice that crunches underfoot. Maybe the ice creaks and groans, as our characters shifts their weight from one foot to the other, or a freezing wind is blowing in huge gusts. All these elements increase the feeling that the viewer is really there watching the action.

The categories of Foley sounds

Foley sounds are often placed in one of three categories:

1. Footsteps which occur incredibly often in most movies
2. Movement sounds like rustling clothing or swinging fists
3. Specific sounds like zippers or creaky doors

When movie soundtracks were in their infancy back in the 1920s and 30s, the entire audio track had to be recorded on a single track. Now with the invention of multitrack recording and digital editing, the audio track can be recorded in a few takes and can be built of many different layers of sound.

Coconut Hooves

Interestingly, some things when recorded don’t sound like themselves. Or rather, they don’t sound how people expect them to sound. Often objects are recorded that mimic the sound of something else in a more dramatic way.

Celery, apples or acorn shells are sometimes crunched to replicate the sound of breaking bones and crushed skulls. Cornstarch or coffee grounds can be used for crunchy snow or desert dust, and of course, the old classic, coconuts used to mimic the sound of galloping horse hooves.

Let’s not forget the variety of ways a rusty hinge can be used. How would the horror industry survive without the additional ambience of a creaking door on a spooky house or corroded graveyard gate?

The Sounds of Science

In the late 1970s, Ben Burtt pioneered sci-fi sound FX design with his work on the first Star Wars movie. He created the iconic lightsaber noises from the sound of old film projector motors. He mixed this with an electronic buzz which he found accidentally when passing an analog TV set with a microphone.

The sound was then played back through a speaker and re-recorded by swinging a microphone in front of the speaker to capture the sound. This created movement in the sound and the fluctuations in volume and distance gave the realistic effect of the lightsabers being swung backward and forward. Ingenious stuff.

Spaces, rooms and ambient sounds

Though not the most noticeable of sound FX, ambience is a very necessary part of the audio track to make a scene believable. Ambient tracks can be anything from the sounds of birds, lawn mowers, people chatting in a bar or the echo of a huge cave full of treasure.

This can be hard to believe but even natural room sounds in a movie are artificially generated. The dialogue is captured as close as possible to the actors and if there is too much echo or room sound, the dialogue is re-recorded in a studio. This is necessary for the consistently high quality audio that movie production demands.

This means that the natural ambience of the setting must be replicated with digital reverb, which adds the natural echo you would find in different sized rooms. A short sample of audio is often recorded on-set during filming, and this is used as reference so the space's natural ambience can be replicated during post-production.

The world of TV and movie soundtracks is really fascinating stuff. We hope you enjoy them even more, now you know all the work that goes on behind the scenes.