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Alexander Graham Bell, we can hear you now

Photonics Spectra
May 2012

Linguists, historians and even musicians could benefit from noninvasive optical scanning technology that enables us to hear voices and sounds that were recorded more than a century ago.

Unlocking these sounds is part of a collaborative sound recovery project involving scientists at Lawrence Berkeley National Laboratory (LBNL) in California and curators at the Library of Congress and the Smithsonian Institution, both in Washington. The team has tested the process on six recordings using imaging equipment installed by LBNL at the Library of Congress.


Participants in a sound recovery project, Carlene Stephens and Shari Stout, curators at the National Museum of American History, handle an early glass disc record. Images courtesy of National Museum of American History, Smithsonian Institution.


Using a digital scan made from one of the very earliest sound recordings, the group got to hear a male voice recorded in the 1880s. Originally recorded on a glass disc with a beam of light, the voice originates from early experiments in sound recording conducted in Washington by Volta Laboratory Associates – inventors Alexander Graham Bell, Chichester Bell and Charles Sumner Tainter.

Until recently, this historical recording has remained silent in storage at the Smithsonian Institution. Many other early sound recordings could be brought back to life with the new technology as well, including those of musical artists, poets and writers; extinct Native American languages also could be revived.

The sound often is inaccessible because of the fragile, damaged, varied or obsolete technology in which it is embedded. The scanning method preserves the original hardware and essentially repairs some of the existing damage.


This electrotyped copper negative disc of a sound recording was deposited at the Smithsonian Institution in 1881 in a sealed tin box. It contains a tone, a male voice counting numbers, and then two more tones.


“These recordings were made using a variety of methods and materials such as rubber, beeswax, glass, tinfoil and brass, as the inventors tried to find a material that would hold sound,” said Carlene Stephens, curator at the Smithsonian’s National Museum of American History. “We don’t know what is recorded, except for a few cryptic inscriptions on some of the discs and cylinders, or vague notes on old catalog cards written by a Smithsonian curator decades ago.”

The first 90 years of sound recording are dominated by mechanical carriers, some in cylinder form, where the groove varies in depth, and some in disc form, where the stylus moves from side to side in the spiral groove, according to a recent report by Carl Haber, a scientist at LBNL.

The optical technique creates a high-resolution digital map of the disc or cylinder. The digital version is then processed to remove scratches or skips that may have appeared on the original recording. Software then calculates the motion of a stylus moving through the grooves of the disc or cylinder, reproducing the audio content and producing a standard digital sound file.

Two-dimensional imaging using a line-scan camera is suitable for a disc with a lateral groove, and 3-D imaging using a confocal scanning probe is required for a cylinder with vertical groove modulation, Haber reported.



Hear for Yourself

To listen to the early sound recordings, visit the Volta Labs Recordings channel on YouTube, provided by the Smithsonian Institution’s National Museum of American History: http://tinyurl.com/cp8ooxt.


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