Groovy Pictures: Extracting sound from images of old audio recordings

Songs and words preserved on antique vinyl records and wax cylinders become more precious with each passing day. They also grow increasingly fragile and are especially vulnerable to damage if played.

Now, researchers using optical-scanning equipment have made exquisitely detailed maps of the grooves of such recordings. By simulating how a stylus moves along those contours, the team has reproduced the encoded sounds with high fidelity.

Libraries with collections of old recordings “don’t want to queue up an antique piece of material every time you want to hear it,” notes particle physicist Carl H. Haber of Lawrence Berkeley (Calif.) Laboratory, codeveloper of the new scanning approach. Instead, those institutions seek to extract sound from delicate recordings and preserve it electronically. In that form, it can be played back repeatedly without harming the original and also made available on the Internet.

A few years ago, Haber heard on the radio that archivists needed ways to nondestructively extract sound from old recordings. He and his Berkeley lab colleague Vitaliy A. Fadeyev, who make arrays of sensors for tracking minute particles in powerful accelerators, realized that their own work was relevant. To align their arrays, they scan sensor surfaces by using a microscope with submicrometer resolution. After hearing of the archivists’ problem, “we thought, ‘Wow! Why don’t they just do it optically?'” Haber recalls.

The scientists used their microscope to make a two-dimensional map of the grooves on a 78-revolutions-per-minute shellac disc of a circa 1950 recording of “Goodnight Irene.” They also wrote software that calculates the velocity with which a stylus would move in the mapped grooves. A sound clip from the virtual disc sounded better than the same section played back from the original disc with a stylus did, Haber and Fadeyev reported in the December 2003 Journal of the Audio Engineering Society.

Recently, the Berkeley physicists, along with other U.S. and British researchers, showed that the approach also worked well on a 1909 wax-cylinder recording. Because wax cylinders store sound as up-and-down undulations of the groove, rather than as side-to-side ones, as discs do, the team turned to three-dimensional scanning using an instrument known as a confocal microscope.

Haber described their work on May 25 in New York City at a meeting of the Acoustical Society of America.

The new mapping technique could enable archivists to retrieve recordings from damaged or broken records and discs, comments Peter G. Alyea of the Library of Congress in Washington, D.C., which is funding some of Haber and Fadeyev’s work. The method could also solve the looming problem of playing archived recordings after old types of playback equipment become unavailable, he adds.

Using existing equipment, the scientists would require an entire day to scan one full wax cylinder, they estimate. One of their next tasks is to find ways to speed the process.

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