Mariyana Pavlova

Mariyana Pavlova, born in the town of Smolyan in the Rhodope Mountain, officially received her certificate from the Guinness Book of World Records, which recognizes her as the female singer with the lowest voice on the planet, at 57.9 Hz.
https://www.guinnessworldrecords.com/world-records/358819-lowest-vocal-note-by-a-female