In physics class yesterday I managed to figure out that our school's PA system emits a 500Hz tone to signify the beginning and end of a class. So...
A bit of fooling around later, I managed to figure out that the tone could be represented by a square wave. I then reduced the sampling rate to compensate for the fidelity of the system until I got a near-exact replica of what we all hear in school.
Better yet, it passed the test of getting me out of History class five minutes early. Now that's quality!