When most people praise the quality of a duet, they expect to be congratulating two people. But, as a video that’s gone viral this week has proved, that assumption need not always hold true. In just over eight days German singer Anna-Maria Hefele has racked up 4 million views on YouTube by demonstrating her phenomenal ability to sing two separate melodies at the same time.
Hefele’s performance is an example of polyphonic overtone singing, a technique which allows her to produce two distinct notes in perfect harmony.The lower of the two is generated by the vibrations of vocal folds in the larynx: the same process as occurs in everyday speech. This sound wave is said to have a fundamental frequency, as it has the longest wavelength that will fit inside the resonant cavity formed by the speaker’s mouth and throat.