Best Of Opera on Instagram: "🎤 Anna-Maria Hefele — Andesana If you watched our Canon in D overtone video (the one that sounded like TWO singers), you’re hearing the same “how is this possible?” phenomenon here — just in a different piece. What you hear is NOT a duet and NOT added harmony. It’s ONE human voice revealing hidden frequencies that already exist inside the sound: overtones singing (harmonics). That’s why your brain separates it into two layers: a low foundation… and a bright melody f