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A sound follower, also referred to as ''separate magnetic'', ''sepmag'', ''magnetic film recorder'', or ''mag dubber'', is a device for the recording and playback of film sound that is recorded on magnetic film.〔(Audio post production for television and film ) an introduction to technology, By Hilary Wyatt, Tim Amyes, page 73〕〔( Georgia State University ), How record heads work.〕 This device is locked or synchronized with the motion picture film containing the picture. A sound follower operates like an analog reel-to-reel audio tape recording, but using film, not magnetic tape. The unit can be switched from manual control to sync control, where it will follow the film with picture.〔(thefreedictionary.com sepmag )〕 == Operation == Many motion picture cameras do not record audio sound on the film, so in professional film production, there is a need to have the sound recorded and played back on a device that has a double-system recording to tapes, either DAT or Nagra, and then transferred to 16mm or 35mm separate magnetic film. The sound recording would then be synchronized with a movie projector〔(abctvgorehill.com.au ) mag unit at ABC in the 1950s, to play the sound locked to a Film chain〕 or a telecine. Either 35mm film or 16mm film that is fully coated with a magnetic material can be locked, sprocket hole by sprocket hole, to the film with the picture image. On the set, a clapperboard is used to mark the spot where the sound and picture will later be synced.〔(soundonsound.com ) A Practical Guide To Working With Pictures, Part 3,Tips & Tricks, Published August 2000.〕 Typical sound followers lock by using 240 Hz bi-phase interlocking pulse signals to sync sound to film.〔(digitalpostservices.com ), Glossary of Film Terms〕 The 240 Hz bi-phase is ten times the 24-frame rate.〔(The Greater London Industrial Archaeology Society ) Syncwriter 1983–1986, Film and Sepmag〕 Sound followers are found in many post-production studios for record and playback and in movie theater for sound playback.〔(n70mm.com ), Todd-AO studios, use of room full of Magnatech units in post production.〕 In telecine use, the 24 frames per second is slowed to 23.976 frames/s to lock to SDTV and some HDTV standards, thus the digital bi-phase pulse is 239.76 Hz.〔(History of Telecine at the BBC, 1994 )〕 The average feature film requires a large amount of 35mm film. One second of 35mm film uses 1.5 feet of film, moving at . One minute of film uses , and one hour uses . So, a two-hour movie with previews uses 11,250 feet or of film. For 16mm film, these numbers are all divided by 4. Because a two-hour movie is so long, the whole is divided onto five or six reels. While a film projector uses an intermittent mechanism to play the film, a sound follower and most telecines use continuous motion.〔(The Editors Guild Magazine ), "Math of Movies", Vol. 24, No. 1 – January/February 2003.〕 By having the sound and picture sync this way this would save the expense and time of making an optical print or magnetic sound track strip on the edge of the film.〔(Sound recording ), the life story of a technology, by David L. Morton, Jr.〕 The Sepmag would follow a projector or a telecine or a hand-cranked or motorized film viewer on a workbench. The sepmag sound follower would stay in sync with the film. In post production work, a dubbed sound track of sound effects, or a second language, could be added to other channels of the sepmag.〔 *(Film into video: a guide to merging the technologies ) by Stuart Blake Jones, Richard H. Kallenberger, George D. Cvjetnicanin, page 169 to 173〕 Sepmag had different record head configurations. A device could have a single mono track, dual two track or 4 track. The tracks are very large and the magnetic film moving at the normal speed of 24 frames per second, gave very good sound reproduction.〔(College of Communication – The University of Texas at Austin ) How to use a Magnatech〕 As such, a mixing studio would have many units, to mix all the sound and effect down to 4, 2 and one track as needed.〔(Stan Ginsel, Video Producer ) Classic Movie Making – What’s a Dubber and Mag Stock?〕〔(The Editors Guild Magazine ) Vol. 25, No.1 page 126- January/February 2004, by Gregg Rudloff, Film Mixing.〕 Magnetic film used is 3 to 5 mils thick, the same as the picture film, so the picture and sound have equal diameters on the film reels. The magnetic film has magnetic oxide coating on the complete width of the film.〔 The first films use were acetate base till 1970, the next base was polyester base. Acetate base can have degradation, the ferric oxide coating and the Acetate base can cause vinegar degradation.〔(Presto ) Page 8, PRESTO – Preservation Technologies for European Broadcast Archives, IST-1999-20013, 3/05/2001〕〔(http://tech.ebu.ch/ ) Preservation and Reuse of Film material for television May 2001, page 5〕 In 1914, the first SEPMAG patent was filed. In 1929, the first sound follower was on the market and by 1941, AC biasing models were sold, giving better sound quality.〔(Audio Engineering Society ) AES E-Library Magnetic Film Transport Based on the SEPMAG Method: Basis and Developmental Program from the First Unit up to the Present Time〕 The Stille SEPMAG transport was one of the first SEPMAG systems.〔(Audio Engineering Society ) Audio Technology in Berlin to 1943: Magnetic Sound Activities – Heinz H. K. Thiele〕 Some of the older sound followers' interlock speeds were too slow to keep up with the high speed shuttle speeds of modern telecines; therefore, some 240 Hz bi-phase buffers were made to help solve this problem. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sound follower」の詳細全文を読む スポンサード リンク
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