Carl Haber’s IRENE—Reconstructing Audio with Imaging Technology
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.