Boventoon zingen or singing two tones at the same time

This phenomenon is self explanatory.

Ms. Hefele:



Now let’s include this in the next challenge?
Enjoy.
Kind regards, Gus

Evil

This is Evil .... I say.        

If you want bionic stuff like this in a challenge then I'm pretty sure @Monty Cash Music  will win.

Ha @Bill from November Sound I'm flattered!

This is beautiful I say, the first example sounds a lot like Mongolian throat singing.

For example, check this out, can be heard in some of this Tatar folk music (in the second and third song in this mix) --