I have just been listening to some Tibetan monks chanting, does anyone know the name of the style?

when the voice goes so low it almost sounds like bass (if that makes sense..) here is a link to the video a href="http://www.youtube.com/watch?v=YyStv12eBTM&feature=relmfu" rel="nofollow"http://www.youtube.com/watch?v=YyStv12eB…/a the bit i like is at 50 seconds, cheers for any help!