Those music files -- be they MP3, AAC or WMA -- that you listen to on your portable music players are pretty crap when it comes to accurate sound reproduction from the original recording. But just how crap they really are wasn't known until now.

Audio data compression, at its heart, is pretty simple. A piece of software compresses a piece of digital audio data by chopping out redundancy and approximating the audio signal over a discrete period of time. The larger the sample time-period, the less precise the approximation. This is why an MP3 with a high sampling rate (short sample times) is of higher quality than an MP3 with a low sampling rate.

To test if the human ear was accurate enough to discern certain theoretical limits on audio compression algorithms, physicists Jacob N. Oppenheim and Marcelo O. Magnasco at Rockefeller University in New York City played tones to test subjects.