Development of an optical sound reproduction system for negative phonograph cylinders

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It was found recently that many negative phonograph cylinders have been preserved in Berlin, Germany. Since, in the negative cylinder, sound information is encoded in convex portions of the inside wall of the cylinder, a conventional phonograph is inapplicable to the sound reproduction. In the present study, we have developed an optical sound reproduction system for the negative cylinders.1. Compact optical headSound information is recovered by detecting height variations of the sound track on the inside wall of the negative, To this end, a compact optical head to be inserted into the cylinder was designed and constructed using a laser diode, small lenses, mirrors, a beam splitter and a PSD.A relay optics consisting of a lens and a pinhole was inserted in the detection optics to reject stray light effectively and to improve an SNR of reproduced sounds.2. Driving unitIn the driving unit, the negative is held by inserting it into a larger holding cylinder and by fixing it to the holding cylinder with six screws. The holding cylinder is rotated by a DC motor, and the cylinders and motor are mounded on the translation stage, which is driven by a pulse motor to keep a tracking by the laser beam.3. Entire system and sound reproductionAbove components were combined into a system and controlled by a control unit, and the final performance of the system was examined and verified. Sounds were reproduced successfully from some old negative cylinders, in which cylinders of koto and shamisen played and recorded by a Japanese old company of drama shows, led by Otojiro Kawakami, are included.