Augmented reality usually refers to the overlaying of digital images or information onto a user's view, but it's not all visual. To wit, there's an iPhone app called Hear that does augmented aural reality — and it's a blast. Hear works by taking in the ambient sound from around you and subjecting it to a variety of processing filters before channeling it into your headphones. I'm already hooked on the Happy mode, which generates a series of differently pitched echoes for every sound you make. It had me mooing in no time at all, and I'm the sort of humorless grump that isn't easily induced into making animal noises.
It's difficult to describe in words the effects that this app creates. Can I get away with just saying that they're very effective, trippy, entertaining, and — since the app's free — worth trying out for yourself? The Office filter is unnervingly good at scrambling all nearby sound, turning office conversations into a wall of diffuse noise that doesn't distract. The Talk mode autotunes speech, Super Hearing makes every little detail around you audible, and Sleep is a psychedelic aural mess that promises to induce "the most deep and surreal dreams of your life."