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Acetate disc
An acetate disc, also known as a test acetate, dubplate (a term from Jamaican reggae culture, now also applied to individually recorded discs of solid plastic), lacquer (a technically correct term preferred by engineers in the recording industry), transcription disc (a special recording intended for, or made from, a radio broadcast) or instantaneous disc (because it can be played immediately after recording without any further processing), is a type of phonograph (gramophone) record, a mechanical sound storage medium, widely used from the 1930s to the late 1950s for recording and broadcast purposes and still in limited use today.
Unlike ordinary vinyl records, which are quickly formed from lumps of plastic by a mass-production molding process, a so-called acetate disc is created by using a recording lathe to cut an audio-signal-modulated groove into the surface of a special lacquer-coated blank disc, a real-time operation requiring expensive, delicate equipment and expert skill for good results. They are made for special purposes, almost never for sale to the general public. They can be played on any normal record player but will suffer from wear more quickly than vinyl. Some acetates are highly prized for their rarity, especially when they contain unpublished material.
Acetates are usually made by dubbing from a master recording in another medium, such as magnetic tape. In the vinyl record manufacturing process, an acetate master disc is cut and electroforming is used to make negative metal molds from it; each mold, known as a stamper, can be used to press thousands of vinyl copies of the master. Within the vinyl record industry, acetates are also used for evaluating the quality of the tape-to-disc transfer. They were once a favored medium for comparing different takes or mixes of a recording, and if pressed vinyl copies of an impending new release were not yet available, acetates were used for getting preview copies into the hands of important radio disc jockeys.
== Physical characteristics ==
Although once produced in a wide range of sizes (from less than 7 to more than 16 inches in diameter) and sometimes with glass core discs, the examples most commonly encountered today are 10, 12, or 14 inches in diameter and consist of an aluminum core disc coated with black nitrocellulose lacquer, commonly but incorrectly called "acetate". The term "acetate" derives from the material used in examples cut before 1934, when the substrate was in fact cellulose acetate. Cellulose acetate was only in use for a short while, but the name "acetate" for these discs persisted. Blank discs were traditionally produced in several different grades, with the best and costliest grade featuring the sturdiest core, the thickest coating and the most perfectly flawless mirror-like surfaces. These top-quality blanks were intended for cutting the master discs that, once silver-coated, would be electrodeposited with nickel in order to electroform parts used in making stampers (negative profile metal molds) for pressing ordinary records. Lower-quality blanks were considered adequate for non-critical uses such as tests and demo discs. Lower-grade blanks were formerly made for home use by amateurs and may be very thin and flexible, may have a cardboard rather than a metal or glass base, and may have noticeably dull or slightly orange-peel-textured surfaces. In addition to the usual central ''spindle hole'' with these lower quality "dubs", there is traditionally at least one ''drive hole'' in the label area, meant to be engaged by a special pin that prevents the disc from slipping on the turntable during the recording process on lathes that don't have a vacuum turntable. Drive holes are often hidden by labels applied after the recording was cut, but they can usually be detected by careful inspection of the label or by holding the disc up to a light bright enough to penetrate the labels. Such holes are not present in lacquer masters—only "dubs". The second hole would interfere with the electroforming process done to master lacquers. Professional mastering lathes use vacuum turntables that hold the workpiece (lacquer) in place with suction. One pump usually provides suction for both the turntable and the chip tube that pulls away the fine string of (nitro-cellulose) lacquer removed by the groove-cutting stylus.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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