Listening to old records without lowering a needle

An old record may be difficult to play with a needle: it may be fragile, or suitable playback equipment may be hard to find. IRENE, presented by the Library of Congress, uses optical equipment to record the grooves in its surface instead.

The grooves contain tiny variations corresponding to sound. On a turntable, a stylus follows those variations. The optical method calculates the groove’s path from captured data and converts it into sound. Different media require different surface information, obtained through two-dimensional images or measurements of height.

In images published by the library, grooves appear as narrow bands. Their sides and bottoms reflect light differently. The boundaries may not appear the same on a smooth record and one that scatters light from a rough surface. Researchers therefore adjust the illumination and the information they extract.

To fit minutes of sound onto one side, the groove is wound into closely spaced turns. In the captured image, neighboring turns must be distinguished so one continuous path can be followed through its small variations. Reading those changes in sequence turns a fine visible line into an audio signal.

Another advantage is that the captured surface data can be kept. If sound-reconstruction methods change, the existing data may, where suitable, be processed again. Alongside preserving the physical record, deciding how much information to retain from the first reading becomes part of restoration.

Here, a photograph records more than a record’s appearance. It supplies data from which sound can be calculated. When direct playback would put an object at risk, reading the surviving grooves offers another route from preservation to listening.