I just watched a video called Genghis Blues - a documentary in which bluesman Paul Pena travels to Tuva (part of Russia now, near Mongolia) to perform throat singing in its place of origin. The gist of the technique is that the Tuvans have learned how to isolate the undertones and overtones that are always present when we sing. The result is a sound that is not to be believed. Just another example of how remarkable the human voice is. Recommended viewing.

dw
BTW, I purchased this DVD at the Discovery Channel retail store.