MusicOvertone singer Anna-Maria HefeleTo view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 videoMusicSimon Broll11/02/2014November 2, 2014Starting with an undertone, Anna-Maria Hefele uses special mouth and tongue movements to filter out sound frequencies. To the ear, it sounds like two separate tones. Millions have seen her on YouTube.https://p.dw.com/p/1DeE1Advertisement