The phonautograph was the earliest known invention of a sound inscription device. It was invented by Frenchman Édouard-Léon Scott de Martinville and patented on March 25, 1857. It could transcribe sound to a visible medium, but had no means to play back the sound after it was recorded. The transcriptions, known as phonautograms, were first successfully played back using computer technology in 2008.
The device consisted of a horn or barrel that focused sound waves onto a membrane to which a hog's bristle was attached, causing the bristle to move and enabling it to inscribe the sound onto a visual medium. Initially, the phonautograph made recordings onto a lamp-blackened glass plate. A later version (see image) used a medium of lamp-blackened paper on a drum or cylinder. Another version would draw a line representing the sound wave on a roll of paper. The phonautograph was a laboratory curiosity for the study of acoustics. It was used to determine the frequency of a given musical pitch and to study sound and speech; it was not understood at that time that the waveform recorded by the phonautograph was in fact a recording of the sound wave that needed only a playback mechanism to reproduce that sound.
In 2008, phonautograph recordings were for the first time played back as sound by American audio historians. The team accessed Leon Scott's phonautograph papers which were stored in France's patent office and the Académie des Sciences. They then optically scanned the etched paper recordings into a computer program developed a few years earlier for the Library of Congress. The sound waves on the paper were then translated by the computer into audible sounds. One recording, created on April 9 1860 was revealed to be a 10-second recording (low fidelity but just recognizable) of a singer performing the French folk song "Au Clair de la Lune". This phonautogram is the earliest known recording of a human voice to be played back. predating Frank Lambert's 1878 recording of a talking clock by nearly two decades and the Edison Company's 1888 phonographic recording of a Handel concert by nearly three decades.
Since the above recording was recovered, the same team have succeeded in recovering a 1859 recording of a 435 Hz tuning fork, (at that time the French standard concert pitch, now internationally 440 Hz), possibly made to test the machine's ability. This latter recording is thus the oldest known recording of a recognizable sound to be played back. An even earlier 1857 recording yielded a sound that may have been a snatch of a human voice, but it is too short to identify it positively.