Definitely an interesting sound, but not my definition of singing. The term "polyphonic singing" makes me want to hear a single person sing in a way such that it sounds like two or more people singing in harmony.
It's only 3:28 long. I think you meant 2:25 since he does a really good overtone at about 2:30. Thanks for this perfect example. Usually I'm the only one who knows wtf I'm talking about when I mention such obscure things.
There is at least one person who does Amazing Grace with a moving "bass" line underneath. Most people just stick to the key note though, which in my mind is cheating since the whole song is basic pentatonic to begin with.
So I definitely agree that the level one might consider a solo song, with melody and changing chord progression and/or oblique harmony, sung by a single person in solo, is rather rare.
His live song Drive has 2 distinct types of overtone singing in there. Some people think he's a tad weird, but his skill is unmistakable once you get used to "do" being the primary lyric.
