During a sports broadcast such as the Olympics, the network showing the program will frequently use several on-field microphones and even add sound effects to match the viewer’s expectations of what the event should sound like. Many sounds – such as an arrow flying toward a target, or a balance beam creaking under the gymnast’s weight – are simply not audible, even from close up. In this case, pre-recorded sound effects are added while the program is being broadcast.
An interesting read:
Some Olympic Sounds Are Fake – Boston.com
