The phonautograph is the earliest known device for recording sound. Previously, tracings had been obtained of the sound-producing vibratory motions of tuning forks and other objects by physical contact with them, but not of actual sound waves as they propagated through air or other mediums. Invented by Frenchman Édouard-Léon Scott de Martinville, it was patented on March 25, 1857. It transcribed sound waves as undulations or other deviations in a line traced on smoke-blackened paper or glass. Scott believed that future technology would allow the traces to be deciphered as a kind of "natural stenography". Intended as a laboratory instrument for the study of acoustics, it was used to visually study and measure the amplitude envelopes and waveforms of speech and other sounds or to determine the frequency of a given musical pitch by comparison with a simultaneously recorded reference frequency.
It did not occur to anyone before the 1870s that the recordings, called phonautograms, contained enough information about the sound that they could, in theory, be used to recreate it. Because the phonautogram tracing was an insubstantial two-dimensional line, direct physical playback was impossible in any case. However, several phonautograms recorded before 1861 were successfully converted and played as sound in 2008 by optically scanning them and using a computer to process the scans into digital audio files.
