The dozens of sounds that came loaded on the tablet for each team were originally made for the PlayStation game MLB: The Show. Each noise has three levels—small, medium, and large—and layering can create additional ones. (An extra-loud cheer can be done by playing all three levels at once.) And teams can choose to customize the program with noises of their own, too. The A’s, for instance, added a recording of their super-fan The Banjo Man. The Brewers remixed some of the sounds to fade in and out more gradually.
I saw something about soccer matches using crowd noise from the EA FIFA games as well, and it just pleases me to no end that video games have gotten so good at replicating this stuff that when the real teams needed to make things sound more normal this year, they went right for video games.
The fact this is being done from iPads, is just the cherry on top.