Operating instructions

G-3
Many theaters were equipped for magnetic sound in the 1950s, even
though the playback equipment was expensive. Many films were issued
with magnetic soundtracks, although magnetic prints were, and remain,
much more expensive than optical sound prints (35 mm magnetic prints
cost at least double their optical equivalents, and today’s 70 mm magnetic
prints cost up to fourteen times as much).
By the 1970s, however, the film industry declined overall, with fewer
films and fewer theaters. The expense of magnetic release prints, their
comparatively short life compared to optical prints, and the high cost of
maintaining magnetic theater equipment led to a massive reduction in
the number of magnetic releases and theaters capable of playing them.
Magnetic sound came to be reserved for a only handful of first-run
engagements of “big” releases each year. By the mid-1970s, movie-goers
were again usually hearing low fidelity, mono optical releases again,
with only an occasional multitrack stereo magnetic release.
Dolby Gets Involved
The situation that prevailed in the mid-1970s completely changed by the
late 1980s. Thanks to new technology and a turnaround in the financial
decline of the industry, almost all major titles today–accounting for 80%
of the boxoffice–are released with wide-range multichannel stereo
soundtracks.
The breakthrough was the development of by Dolby Laboratories of a
highly practical 35 mm stereo optical release print format originally
identified as Dolby Stereo. In the space allotted to the conventional
mono optical soundtrack are two soundtracks that carry not only left
and right information as in home stereo sound, but also information for
a third center-screen channel and–most notably–a fourth surround
channel for ambient sound and special effects.
This format not only enabled stereo sound from optical soundtracks,
but higher quality sound as well. Various techniques are applied both
when the soundtrack is recorded and when it is played back to improve
fidelity. Foremost among these is Dolby noise reduction to lower the
hissing and popping associated with optical soundtracks, and
loudspeaker equalization to adjust the theater sound system to a standard
response curve.
All this means that these prints can be reproduced in theaters with
Dolby-manufactured cinema processors with far wider frequency
response and much lower distortion than conventional soundtracks. In
fact, the Dolby optical format has led to a new worldwide playback
standard (ISO 2969) for wide-range stereo prints, just as the “Academy”
characteristic applies for mono prints.