The Echonest, a startup out of the Media Lab located in Somerville, MA, just launched an Audio Analysis API which processes MP3s and returns an XML document with a number of features including tempo, loudness, time signature, fades, timbre and a whole lot more. These can be used in a number of different cool demos that they are providing as reader exercises
is there a fee? i like odd and obscure rock tracks and parodys of songs