A sound effects technique for synchronous
effects or live effects.
technique is named for Jack Foley, a sound editor at Universal Studios (he
simultaneously added music and effects to the previously silent film
"Showboat" and the first "Foley" session was born).
What is it about the sound in many student or amateur films that makes them sound so... well... amateur? Even if the fidelity or clarity of the dialogue is good, there is often something empty or thin about the rest of the soundtrack - the action lacks depth and realism. The answer could be that the film makers did not add Foley to the soundtrack.
Foley effects are sound effects added to the film during post production (after the shooting stops). They include sounds such as footsteps, clothes rustling, crockery clinking, paper folding, doors opening and slamming, punches hitting, glass breaking, etc etc. In other words, many of the sounds that the sound recordists on set did their best to avoid recording during the shoot.
The boom operator's job is to clearly record the dialogue, and only the dialogue. At first glance it may seem odd that we add back to the soundtrack the very sounds the sound recordists tried to exclude. But the key word here is control. By excluding these sounds during filming and adding them in post, we have complete control over the timing, quality, and relative volume of the sounds.
For example, an introductory shot of a biker wearing a leather jacket might be enhanced if we hear his jacket creak as he enters the shot - but do we really want to hear it every time he moves? By adding the sound in post, we can control its intensity, and fade it down once the dialogue begins. Even something as simple as boots on gravel can interfere with our comprehension of the dialogue if it is recorded too loudly. Far better for the actor to wear sneakers or socks (assuming their feet are off screen!) and for the boot-crunching to be added during Foley.
steamy sex scene was probably created by a Foley artist making dispassionate
love to his or her own wrist.
Foley is usually performed by Foley performers or artists. Ideally they stand on a Foley stage (an area with a variety of possible surfaces and props) in a Foley studio (a specialized sound studio), though any post production sound studio will do with a little modification. The Foley artists can clearly see a screen which displays the footage they are to add sounds to, and they perform their sound effects whilst watching this screen for timing. The actions they perform can include walking, running, jostling each other, rubbing their clothing, handling props, and breaking objects, all whilst closely observing the screen to ensure their sound effects are appropriate to the vision.
Without Foley, a film sounds empty and hollow - the actors seem to be talking in a vacuum (not literally possible I know - but you get the idea). The sound recordist, if they did a good job, has given us the dialogue and excluded everything else, but our film needs more than this for the picture to come alive. We need to hear the little sounds of clothes, furniture, etc - but we need to control them so they don't obscure any of the dialogue.
Increasingly, many simple Foley effects are done without Foley performers - the sounds are stored electronically and performed by the post production sound engineer on a keyboard whilst watching the vision. Done poorly this type of "Foley" sounds bland and repetitive, and it is nowhere near as flexible as the real thing, but it is much cheaper than renting a Foley stage and paying Foley artists.
Foley can also be used to enhance comedy or action scenes. Watch most comedy films and you'll notice that many of the sounds are enhanced for comic effect, and sometimes the Foley effect is the joke. As for action, most fist fights do not involve the actors really hitting each other, and even if they did we would not be able to record a satisfying punch sound. By punching and variously molesting such objects as cabbages etc, Foley artists can record unique and much more "realistic" action sounds.