How Sound Editing Works

Using Sound Effects

A dog's barking can be added in post production.
A dog's barking can be added in post production.
© Isak Tiner/Photonica/Getty Images

Picture a scene in a movie where a man and a woman are sitting and talking on a bench in New York’s Central Park. As they talk, someone on in-line skates cruises by. You can hear birds chirping in the background and the tree leaves rustling slightly in the fall breeze. In the distance, you can hear the muffled sounds of city life: cars honking, buses rumbling and dogs barking.

Believe it or not, almost none of these sounds were recorded on location. The only sound that was recorded live in Central Park was the actor’s dialogue, captured with small microphones attached to their clothes. All of the other sounds -- the birds, dogs, leaves, car horns, and the zip of the in-line skates -- are really sound effects, added later by the sound editor to create a convincing Central Park soundscape.

Background sound effects are the subtlest. The sound editor uses them to create a mood or ambience. If the scene takes place in an office, the background effects could include phones ringing, people talking quietly in the background and the barely perceptible hum of the air conditioning system.

So where do these background sound effects come from? Some sound editors create their own library of recorded sound effects. They might take a microphone to a crowded beach to capture the sound of kids playing and waves crashing. They could record dozens of different rain storms on different surfaces: tin roofs, pavement, dirt roads, et cetera. When it’s time to add background sound effects to that park scene, they dig through their library for “Central Park: Fall.”

Nowadays, it’s more common for a sound editor to purchase large digital libraries of background effects on CD. These offer a wide variety of audio clips that can be layered into a scene to create a convincing ambience.

Besides background effects, some scenes call for various hard effects -- loud, violent noises like gunshots, punches and door slams. Some of these hard effects can be downloaded from effects CDs, while other are created by people called Foley artists.

Foley artists use unconventional techniques to recreate realistic sounds that sync with the onscreen action. While Foley artists might create some hard effects, they’re best known for supplying the subtle audio details of a scene, like footsteps across a wood floor, the sound of a wine glass being placed on a marble countertop, or the whir of those in-line skates.

Foley artists work on a Foley stage that’s stocked with all the strange props they need to do their jobs. Here are some examples of Foley techniques:

  • Crumpling a bag of potato chips to recreate the crackle of a fire
  • For realistic body kicks and punches, beating a cooked chicken stuffed with raw carrots and celery
  • Rustling a ball of unwound cassette tape to mimic footsteps through the grass
  • Using leather gloves for the flapping of bird wings
  • Loading a slingshot with pennies and washers to capture the sound of bullets whizzing by

Now let’s take a trip back to the pre-digital days when sound editing was all done by hand using magnetic tape.