A recording from 1860 that was never intended to be played has been heard thanks to the work of sound historians Patrick Feaster and David Giovannoni of First Sounds.
The machine for which it was produced in 1860 was created by Édouard-Léon Scott de Martinville and called a phonoautograph. It's original intention was to produce a visual representation of sound on soot-coated paper rather than as a means to playback audio.
Roughly ten seconds in length, the recording is of a person singing “Au clair de la lune, Pierrot répondit” – a snippet from a French folksong. Listen to it HERE.
Oldest recorded voice sings again (BBC)