Édouard-Léon Scott de Martinville's Phonautograms (partially found audio recordings; 1850s-1860s)
Édouard-Léon Scott de Martinville (25 April 1817 - April 26, 1879) was a French inventor known for his experiments with the "phonautograph," the earliest known device that could accurately record sound waves. Although the device was never intended to play back the recordings, modern-day digital photography has made it possible to convert the waves into actual, audible sounds. In 2008, a small team of researchers at firstsounds.org managed to play some of the phonautograms. This made them the earliest known recorded sounds, predating Thomas Edison's early tinfoil experiments for nearly 20 years.
Because of Scott's fascination with visible sound, he spent approximately 20 years recording many different sounds. Of the examples, most of them were recordings of ticking clocks, string instruments, air currents, distant voices, and a tuning fork. One particular example proved to be quite impressive to historians; A recording of a person singing a rendition of "Au Clair de la Lune," a classic French folk tune, recorded on April 9th, 1860. When originally played, historians misread Scott's notes and played it at double speed, making the listener identify the gender of the singer as a woman. However, after many corrections, the recording was played back at the correct speed, and the gender was revealed to be the voice of Scott himself. The Au Clair de la Lune phonautogram is the oldest-known recording to feature a recognizable human voice.
According to several sources, there were recordings from the early 1850s that featured human voices. Unfortunately, the majority of these recordings are either extremely deteriorated, or far too indecipherable to be of any significance. Many people still long to hear these recordings, though, as they were the earliest known recorded sounds made by humans. An infamous rumor surrounds the device; being that Scott had toured the United States in the 1860s with the device, and had at one point, met and recorded the voice of Abraham Lincoln. While it is unclear if this really happened, Scott allegedly recorded Lincoln giving his opinion on slavery. If this recording were to resurface, it would be the earliest surviving sound recording of both the English language and a U.S. president. Historians, however, doubt that such a recording was ever made.
Technology is getting progressively closer to being able to decipher Scott's surviving recordings. There are still many recordings that are yet to be correctly played, which will lead to a treasure trove of historically lost media.