Audio reconstruction of mechanically recorded sound by digital processing of metrological data

For much of recorded sound history, audio information was stored on mechanical media, such as a phonograph disc record or cylinder, through undulations of the surface structure (grooves). The groove shape and position can be reconstructed without mechanical contact using precision optical metrology tools. The surface map thus obtained can be digitally processed to remove noise artifacts due to debris, damage and wear, and to convert the groove positional information into audio data. The viability of this approach was recently demonstrated on a 78 rpm shellac disk using two dimensional image capture and analysis methods and further developments are reported. A three dimensional reconstruction of mechanically recorded sound has been recently completed. The surface of the source material, a celluloid cylinder, was scanned using confocal microscopy methods and resulted in a faithful playback of the recorded information. These results are discussed. The approach holds promise for the reconstruction of valuable historical recordings, using full surface information to improve the sound fidelity, and eventually as a means of automated mass preservation. Fast processing is required for the latter application. Methods to accelerate the scan rates and make these techniques practical for use at working archives are discussed