Why do movie punches sound nothing like real punches?

When a movie hero punches a villain, the thump you hear almost certainly did not come from the fight. Fist-fighting scenes are usually staged by stunt actors and so do not have the actual sounds of blows landing. Likewise, props, sets and costumes are often cheap and lightweight materials that look like the real thing but do not sound like it. So the sound is built afterwards, by people who watch the finished picture and recreate the noises in a studio. This craft is called Foley, after sound-effects artist Jack Foley.

Foley started when talking pictures arrived. Microphones of the time could not pick up more than dialogue, so other sounds had to be added after the film was shot. Foley and his small crew projected the film on a screen while recording a single track of audio that captured their live sound effects, timed so that footsteps and closing doors matched the actors' movements. Some of the tricks are delightful: frozen romaine lettuce makes bone-cracking or head-injury noises.

The best Foley art is so well integrated into a film that it goes unnoticed by the audience, and yet its absence would be obvious. Without these background noises, movies feel unnaturally quiet and uncomfortable. Foley effects even help you judge the size of a space, since a large hall has strong reverberation while a small room has only slight reverberation.

Film sound has another layer. Sound that characters can hear, like voices and a radio playing in the room, is diegetic. Sound that comes from outside the story, such as mood music or a film score, is non-diegetic: only you hear it. A sound designer is the person who plans all of it as one track.