I've found a nice tutorial here: http://www.41post.com/4776/programming/unity-making-a-simple-audio-visualization. It is able to get different frequencies from the sounds and do something accordingly. You can try and change the variables of the particle with it.
Another thing I found is a project which analyses the spectrum of sound. You can download it here.
I also found this tutorial which generates a level based on the sound.
These links no longer works
Try them out and let us know what you thought of them and if they helped! Good luck.