Operating instructions

G-4
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 (made all but obsolete by
the stereo optical format), consistently higher fidelity, and few of the
drawbacks of magnetic formats.
Much of the new technology, including noise reduction and equalization,
also is applied to 70 mm magnetic releases (also originally designated
as Dolby Stereo). Although 70 mm release prints continue to be very
expensive, Dolby improvements brought a resurgence of interest in this
“big” format for road shows where the ultimate in picture and sound
presentation is particularly likely to be reflected in box office figures.
There are six magnetic tracks on 70 mm film, two of which carry low
bass effects. Some 70 mm films also use a technique developed by Dolby
Laboratories to provide two separate surround channels in addition to
the left, center, right, and bass effects screen channels.
The Next Step: Dolby SR
In 1986, Dolby Laboratories introduced a new professional recording
process called Dolby SR (spectral recording). Like Dolby noise reduction,
it is a mirror-image, encode-decode system used both when a soundtrack
is recorded and when it is played back. It provides more than twice the
noise reduction of Dolby A-type, and, moreover, permits capturing
loud sounds with wider frequency response and lower distortion.
35 mm optical soundtracks treated with Dolby SR instead of Dolby
A-type not only sound superb in the more than 10,000 theaters equipped
with special SR processors, they also play back satisfactorily in any
theater. As a result, most Dolby SR titles are released single inventory.
In fact, in theaters equipped with regular A-type processors, the moderate
compression that results helps prevent the louder peaks on SR
soundtracks from overloading the theater’s sound system. This feature
further obviates the need for separate mixes and releases.
And Now - Dolby Digital
The newest film sound development from Dolby Laboratories puts a
six-channel digital optical soundtrack in addition to a four-channel SR