Echoes and Notes on Instagram: "In 2014, German singer and vocal artist Anna-Maria Hefele went viral with a mesmerizing video demonstrating polyphonic overtone singing - a rare vocal technique where one person produces two or more notes simultaneously. Her clear, haunting tones captivated millions, making audiences question what the human voice is capable of. Trained in classical singing and overtone techniques, Hefele explained that the sound comes from manipulating resonance in the vocal tract