One one side of the field was a team of former pro soccer players. On the other, a squad of visually impaired amateurs. The two sides laced 'em up, stretched out their quads and went head to head in a scrimmage, though the matchup was a lot more even than you might expect. It's all part of something called the "Sound of Football" -- the latest experiment from the Pepsi Refresh Project. The idea was to level the playing field, so to speak, by forcing both teams to play a match using only their ears, and a pretty nifty tracking system. Created by Tracab, this system was comprised of 16 cameras covering the entire pitch (including two stereovision cameras placed at mid-field), and used jersey colors to distinguish the home team from the away team, and to identify the referees. This set up, which was deployed during the last World Cup, essentially tracked the position of each player in real-time. This information was then funneled into an iPhone attached to each player's headset, and converted into a surround-sound landscape, using an app created by a company called Society 46. Unique sounds were assigned to both the ball and the goal; turning your head in the direction of one goal would produce one sound, facing the ball would result in another. This allowed each player to get a better idea of his surroundings and of his spatial positioning, though, as many of the pros found out, it wasn't quite as easy as it looked. The designers of this system are now looking to use their technology in other, non-sports arenas, in the hopes of helping the blind and visually impaired "see" more of the world around them. Check out a pair of videos on the match and the technology behind it, after the break.[Thanks, Martin]