Carl Haber’s IRENE—Reconstructing Audio with Imaging Technology

Sometimes the coolness factor of a new technology just overwhelms me and I jump it to the front of the queue. Even with NI Week approaching and all the new technologies at play, I just had to post on Carl Haber’s work using imaging technology to reconstruct audio from old phonograph records. In the Smithsonian and other museums around the world are thousands of old lacquer-plated records with skips, scratches and other defects marring the sound, not to mention the obsolete nature of the equipment used to play them. Carl came up with a vision system that images the LP record and “unrolls” the grooves into a long, unbroken string which his software (called IRENE for Image, Reconstruct, Erase Noise, etc) converts into audio components and even plays it out (minus the skips and scratches). The full story from NPR is here.

Carl’s work comes from particle physics which you can read more about here. Given the strong need for such technology, libraries around the nation (such as the Library of Congress) are pulling him into discussions on implementing the technology.

The technology involves imaging the groove shape with precision optical metrology techniques and then applying digital filtering. For flat records, 2D imaging is sufficient. For Edison-era cylinders, 3D imaging is needed. IRENE images the groove using color coded confocal microscopy. Digital imaging of the groove is analogous to digital time sampling but with respect to the spatial direction. Thus, Nyquist comes into play. To reduce unwanted alias signals, IRENE applies a lowpass filter. Stages controlled by DC servo motors read by linear encoders were used to move the camera over the record.

The paper goes on to describe in great detail the motion/vision control of the system to image a cylinder and account for azimuth changes across the cylinder and the signal processing used to reconstruct the waveforms generated by the imaging system.

Best regards,
Hall T.