Dolby Laboratories CP500 Specifications download pdf (Page 150)

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to the older speakers. The result was to ignore the improved high-frequency

response of the newer, better units.

To forestall compatibility problems, in the late 1930s a de facto standardization set

in, the theater playback response that today is called the “Academy” characteristic.

Theater owners knew what to expect from the films, and therefore what equipment

to install. Directors and sound recordists knew what to expect from theater sound

systems, and thus what kind of soundtracks to prepare. The result was a system of

sound recording and playback that made it possible for just about any film to sound

acceptable in any theater in the world. It was also a system, however, without the

flexibility to incorporate improvements beyond the limitations that existed in the

1930s.

Even with these limitations, for years optical film sound provided higher quality

sound than home phonographs and radios. But by the late 1960s and early 1970s,

superior hi-fi stereo systems had been installed in so many homes that a significant

and influential proportion of the moviegoing public was used to better sound at

home than could be heard in the theater.

Magnetic Sound

In the 1950s, a new method of putting sound on film was introduced as an

alternative to the optical soundtrack. After the picture is printed, narrow stripes of

iron oxide material similar to the coating on magnetic recording tape are applied to

the film. The sound is then recorded on the magnetic stripes in real time. In the

theater, the film is played back on projectors equipped with magnetic heads, similar

to those on a tape recorder, mounted in a special soundhead assembly called a

“penthouse.”

Magnetic sound was a significant step forward, and at its best provided much

improved fidelity over the conventional optical soundtrack. Magnetic sound also

permitted the multiple tracks required by stereophonic sound. The voice of an actor

appearing to the left, center, or right of the picture could be heard coming from

speakers located at the left, center, or right of the new wide screens also being

introduced at this time. Music took on a new dimension of realism, and special

sound effects could emanate from the rear or sides of the theater. The two main

magnetic systems adopted were Twentieth Century Fox’s four-track 35 mm

CinemaScope system introduced for The Robe, and the six-track Todd-AO system

first used for such 70 mm films as Oklahoma! and Around The World in 80 Days.

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).

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Dolby Laboratories CP500 Specifications Page 150