phonautogram

A phonautogram is the visual trace of sound produced by a phonautograph, an early sound-recording device developed by Édouard-Léon Scott de Martinville in the 1850s. In its traditional use, a horn captured the sound, a flexible diaphragm translated the air-pressure variations, and a stylus moved by the diaphragm traced the vibrations onto a soot-coated surface such as paper or glass. The resulting marks form a continuous line that encodes the waveform of the sound. The device was intended for study of acoustics and speech, not for playback of audio.

Phonautograms are historically significant as among the earliest known representations of sound waves and predate the later phonograph technologies introduced by Thomas Edison in 1877. Because the phonautograph was not designed to reproduce sound, the traces could only be listened to again by special equipment or, in modern times, by digitizing and interpreting the visual record. In 2008, researchers successfully converted several phonautograms into audible sound, including a 1860 recording of Au clair de la lune, demonstrating that recognizable audio could be recovered from these early traces.

The term phonautogram literally means “sound-writing.” The phonautograph and its phonautograms contributed to the historical development of audio recording and analysis techniques, providing important insights into the origins of sound recording and the study of voice and music.