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 media. 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. Intended solely as a laboratory instrument for the study of
acoustics, it could be 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.