User`s manual

Dolby
®
CP650 Digital Cinema Processor User’s Manual The Evolution of Dolby Film Sound
B-3
Dolby Gets Involved
By the late 1980s, the situation that prevailed in the mid-1970s had completely
changed. Thanks to new technology and a turnaround in the financial decline of the
industry, almost all major titles by that time were being released with wide-range
multichannel stereo soundtracks, as is the case today.
The breakthrough was the development 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
not only carry left and right information as in home stereo sound, but are also
encoded with 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 were applied to the soundtrack during both
recording and playback to improve fidelity. Foremost among these was Dolby noise
reduction to lower the hissing and popping associated with optical soundtracks, and
loudspeaker equalization to adjust the cinema sound system to a standard response
curve.
As a result, with the installation of cinema processors manufactured by Dolby, stereo
optical prints could be reproduced with far wider frequency response and much lower
distortion than conventional soundtracks. In fact, the Dolby optical format led to a
new worldwide playback standard (ISO 2969) for wide-range stereo prints.
An important advantage of the Dolby optical format was that the soundtracks were
printed simultaneously with the picture, just like mono prints. Thus four-channel
stereo optical release prints cost no more to make than mono prints, and far less than
magnetic prints. In addition, conversion to stereo optical proved relatively simple, and
once the equipment was installed, very little maintenance was required. The result
was multichannel capability equaling that of four-track magnetic 35 mm (which soon
became obsolete), with consistently higher fidelity, greater reliability, and far lower
costs.
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 was a mirror-image,
encode-decode system used during both recording and playback. It provided more
than twice the noise reduction of Dolby A-type, and, moreover, permitted loud
sounds with wider frequency response and lower distortion.
The 35 mm optical soundtracks treated with Dolby SR instead of Dolby A-type not
only sounded superb in cinemas equipped with new Dolby SR processors, but also
played back satisfactorily in all cinemas. This led to the situation today, where the
analog soundtracks on virtually all prints are Dolby SR tracks.