Digital Restoration and Preservation of Audio Recordings

http://www.lbl.gov/Tech-Transfer/techs/lbnl1855.html

[talk title: IMAGING THE VOICES OF THE PAST: Using Physics to Restore Early Sound Recordings] [as if you would have clicked on this thread had I used that for the title!] :)

Here's Prof. Huber's website, which contains lots more information about his work including links to papers and lecture notes/ppt presentations:

http://www-cdf.lbl.gov/~av/

Other sound transfer methods involving physical contact with the recording medium, e.g. using a stylus. For damaged or decaying media, this is risky because it risks further damage to these irreplaceable recordings. Their method is optical, so no direct contact needs to be made.

The physics is actually quite simple. They're using commercially available optical scanning equipment to image the surface of the recording medium (shellac record, wax cylinders, etc.). Their expertise as particle physicists is mainly in the detector design. The speed of the imaging process mainly depends on how much light hits their detector, so having very sensitive detectors and efficient imaging systems is a big deal.

Once the surface profile is recorded, they can "clean up" the recording using standard signal processing techniques: frequency filtering and the like.