NFL Films pioneered the use of in-game audio,Scarpe Adidas Saldi, and the league had long clipped a microphone to the umpire's cap to capture the snap count. Before the 2010 season, though, the ump's position on most plays shifted from the middle of the defense to well behind the offense for safety reasons.
After much experimentation during exhibition games, NFL officials decided to put a microphone in the back of the pads of two players for each team: either the first- and second-string centers or both starting guards.