The main problem with location sound is that you cannot control the sound elements independently. Location sound effects are often engaged in a
losing battle with the dialogue recording. Also the sound recordist usually has too little control over too many other variables to adequately record
In order to create comprehensive and rich sounds, each element of the sound must be distinct, and individually controllable. Only then does the Sound Mixer have the capability to effectively combine and balance all the sound elements in the final sound track. The sounds of galloping horse feet must be separated from the rattle of the carriage, from the bridle and saddle movement tracks, from the dirt spray and so forth.
Replacing and adding sound.
In a scene where our hero explores a dark cave, chances are the cave was actually a set made of plywood and styrofoam. When someone gets hit in the head with a metal pipe, the pipe was more likely a piece of foam rubber.
That's where Foley comes to the dramatic rescue? replacing the squeaky wood surface footsteps with wet rocky gritty ones and the poofey bounce of foam with a metallic impact that hurts.
