4.3.2 35mm Magnetic (four-track stereo) (Motion Picture Sound Formats - release prints intended for projection)
Description
This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.
4.3.2 35mm Magnetic (four-track stereo) (Motion Picture Sound Formats - release prints intended for projection)
When the first CinemaScope (tm) films were produced, Fox had special
release print stock made up, which contained very narrow perforations
(known as `Fox holes'). The idea behind this was to allow for a
magnetic sound- track containing four discrete (not matrixed) tracks
(in the same L/C/R/S configuration as the modern Dolby Stereo (tm)
setups). At the time, the 'scope image was wider than it is now
(because it extended into the area now used for optical tracks), and
thus could not fit an optical track on the print. The magnetic stripes
were applied in the same manner as to 70mm prints.
This idea worked reasonably well, and was used for a number of years
(through the early 1970's) on 35mm prints of all formats (only 'scope
prints required the Fox holes, though), and the sound quality was
excellent, even by today's standards, provided that the magnetic
tracks were in good condition. The problem of this scheme was that,
unlike optical sound, the information recorded on magnetic tracks was
not a permanent part of the film, and could be intentionally or
accidentally erased, simply by being placed too close to magnetic
fields, like those found in electric motors (such as those used on
rewind benches). Even reels and cans can become magnetized, sometimes
erasing all or part of the magnetic track, requiring that it be
re-dubbed, at great expense. Further, the magnetic sound heads
required frequent cleaning in order to keep them sounding good.
With the invention of Dolby (tm) `A' noise reduction and the
application of this technology to optical tracks, magnetic sound lost
some of its quality advantage over optical, and it has always been
substantially more expensive than optical to print (as prints had to
be dubbed in real time, whereas optical could be printed at the same
time and speed as the picture). Thus, magnetic sound fell into disuse,
and is no longer commonly used, although, before digital sound became
workable, special prints were made with magnetic tracks for showing in
select theaters for `special engagements' and the like.
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