This Might Melt Your Brain: Anna-Maria Hefele Sings 2 Notes At Once

The overtone series is the sonic example of the Golden Ratio, and it underlies all music (and all sound, really), no matter where the music comes from. Brass players are intimately familiar with the overtone series (also known as the harmonic series), even if they don’t know what it’s called. Produce sound through any tube (like didgeridoo, shofar, flute, bugle, trumpet, garden hose, etc.) while keeping the length of the tube the same (i.e. don’t push keys or valves), and you’ll hear the overtone series. With practice, you can do it with your voice, too, as demonstrated by singer Anna-Maria Hefele in the video below. After her demonstration, there’s a couple more video of what overtone singing sounds like in a piece of music.