Binaural Beats
About 10 years ago a friend asked me about binaural beats. I had to admit at the time that I was oblivious, and had never heard of them. He proceeded to describe a fun audio effect, one that only works through a pair of headphones. If you play an audio tone (frequency) in each ear, and make the tone in each ear a little different, the difference between the frequencies of these two tones - their interference pattern - can be heard as a third audio tone that sounds like it's originating from somewhere between your ears. So, if you play a 550Hz tone in your left ear, and a 500Hz tone in your right ear, you will also “hear” a 50Hz tone between your ears: 550 - 500 = 50.
