Specifications

E-3
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.
An important advantage of the Dolby optical format is that the soundtracks are
printed simultaneously with the picture, just like mono prints. Thus a four-channel
stereo release print costs no more to make than a mono print (although it is more
expensive to record and mix in stereo than in mono). Conversion to Dolby optical
is relatively simple—more than 28,000 theaters worldwide have done so—and,
once the equipment has been installed, very little maintenance is required,
particularly when compared to magnetic stereo playback systems. Moreover, print
life is as long as that of conventional mono optical prints, unlike magnetic prints.
The result is multichannel capability equaling that of four-track magnetic 35 mm