Saphir

Abstract

The goal of optical playback of analogue audio discs records has been pursued since at least 1929. Several different approaches have been demonstrated to work. But in most cases the playback quality is worse than using mechanical playback. The Saphir process uses a specifically designed colour illuminator that exploits the reflective properties of the disc material to highlight subtle changes in orientation of the groove walls, even at highest frequencies (20kHz). A standard colour camera is used to collect rings of pictures from the disc. Audio signal is extracted from the collected pictures automatically, under user control. When colour signal is not useable, track slope can be used as an alternative. The process is slow—several hours per disc—but has a wide range of operation on recorded and printed discs, from earliest Berliner recordings to recent vinyl records, and its strength is at decoding direct-recording lacquer discs. An Elementary Shortest Path Solver with a reward (negative cost) on the number of turns is used to re-connect all the sub-tracks obtained, allowing to reconstruct, with limited human intervention, the correct playback order. We describe the approach and present the main advantages and drawbacks. The process was used to play back a number of extremely damaged (broken, de-laminated…), physically unplayable records.