overtone singing

Overtone singing is a vocal technique that allows a person to produce two distinct sounds, on the one hand the drone, the basic pedal-pedal, on the other hand harmonic variations of the basic sustained sound. See: https://en.wikipedia.org/wiki/Overtone_singing

There are several examples on the web, including: https://www.youtube.com/watch?v=hKbaKN9Hu_U