Phonautograph

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.

[5] One day while editing Professor Longet's Traité de Physiologie, he happened upon that customer’s engraved illustration of the anatomy of the human ear, and conceived of "the imprudent idea of photographing the word."

In 1853 or 1854 (Scott cited both years) he began working on "le problème de la parole s'écrivant elle-même" ("the problem of speech writing itself"), aiming to build a device that could replicate the function of the human ear.

As the glass plate was slid horizontally in a well formed groove at a speed of one meter per second, a person would speak into the trumpet, causing the membrane to vibrate and the stylus to trace figures[5] that were scratched into the lampblack.

[13] By late 1857, with support from the Société d'encouragement pour l'industrie nationale, Scott’s phonautograph was recording sounds with sufficient precision to be adopted by the scientific community, paving the way for the nascent science of acoustics.

The phonautograms were then digitally converted by scientists at the Lawrence Berkeley National Laboratory in California, who were able to play back the recorded sounds, something Scott had never conceived of.

Before he was able to put his ideas into practice, the announcement of Thomas Edison's phonograph, which recorded sound waves by indenting them into a sheet of tinfoil from which they could be played back immediately, temporarily relegated Cros's less direct method to obscurity.

Possibly this was because the few images of them generally available in books and periodicals were of unpromising short bursts of sound, of fragmentary areas of longer recordings, or simply too crude and indistinct to encourage such an experiment.

[17] Nearly 150 years after they had been recorded, promising specimens of Scott de Martinville's phonautograms, stored among his papers in France's patent office and at the Académie des Sciences, were located by American audio historians.

Later, generally available image-editing and image-to-sound conversion software, requiring only a high-quality scan of the phonautogram and an ordinary personal computer, were found to be sufficient for this application.