Optical technology used to play back old sound recordings

Smithsonian : A wealth of early sound recordings made by Alexander Graham Bell and his assistants in the late 19th century have long remained “mute artifacts” because the method of playing them back was unknown. Now more than a century later, Bell’s voice has been heard for the first time. Researchers at the Smithsonian’s National Museum of American History, which holds a cache of more than 400 of Bell’s wax-and-cardboard disks and cylinders, teamed up with researchers at the Library of Congress and Lawrence Berkeley National Laboratory (LBNL). To create digital audio files of Bell’s recordings, LBNL researchers used the optical measurement technique they had developed to align the silicon detectors in the ATLAS experiment at CERN. They took multiple high-resolution images of the soundtracks, moving the camera in a spiral pattern to follow the path of the grooves, then used a computer to calculate the sound pressure waveform and used the data to create the audio file. The result was the sound of muffled voices reciting Hamlet’s soliloquy, number sequences, and “Mary Had a Little Lamb.” By deciphering notes scratched in wax on one of the disks, dated 15 April 1885, they discovered a recording of Bell himself. Perhaps reminiscent of Bell’s father, who was a renowned elocution teacher, Bell can now be heard making the ringing declaration, “In witness whereofâmdash;hear my voice, Alexander Graham Bell.”