4.2.1 16mm Optical (monophonic) (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.
4.2.1 16mm Optical (monophonic) (Motion Picture Sound Formats - release prints intended for projection)
The first sound-on-film 16mm prints, made in the 1940's, used an
optical system, like that used on the 35mm prints of the time. An
optical track consists of an image of a `wave'-like clear band which
allows differing amounts of light to pass through it upon playback
(this is called a `variable area soundtrack'; `variable density
soundtracks' were also tried at one time-they did not use a band of
clear film, but rather the entire soundtrack area varied in density,
or transparency. This gave a slightly better frequency response than a
variable-area track, but resulted in increased background noise, due
to film grain. They are no longer used). The sound is reproduced by
means of an exciter lamp, which shines through a small lens onto the
optical track area of the film. This light is focused onto a solar
cell on the opposite side of the film. The solar cell varies its
electrical resistance based upon the amount of light which is shining
on it. Thus, as the `wavy' band gets wider, more current can pass
through the solar cell, which causes the loudspeaker to vibrate more,
which results in a louder sound. This system is rather primitive, but
it is inexpensive, as the sound is printed on the film at the same
time as the picture, whereas magnetic systems require a separate
`sounding' step after the picture is printed.
Sound quality is not particularly good, but has been improved in
recent years by various methods, including the printing of two
identical tracks which are adjacent to each other. This method allows
the two tracks to cancel out each other's flaws or at least to cover
them up (in theory). Whether or not this actually improves sounds
quality is a topic of debate. Thus, Although it is technically
possible to produce a stereo optical track in 16mm, no one has yet
exploited this potential on a wide-scale basis, as there is no
commonly available equipment to shoot a stereo track, or to reproduce
it. A few test prints were made in this format, however.
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