Some Working Characteristics of the Colortek
The Audio Spectrum.
Theoretically, it appears desirable to reproduce the entire audio spectrum,
although in reality this will be limited for some time due to available equipment.
Normal theater transducers are deficient at both ends of this spectrum. The new
288-G series Altec high-frequency drivers have corrected the deficiency in the
top-end response. But there is no easy answer to the low-end problem, due to
the design of the universally used bass cabinet (which cuts off steeply below
40 Hz), and the desirability persists to reproduce the low-end frequencies as
well as the rest of the spectrum. The only dramatic use of low frequencies in
recent times was made by the Sensurround system. As an integral part of the
Colortek system, components have been developed specially for the better
reproduction of low frequencies. They form a third speaker network in the range
from 20 to 80 Hz to cross over with, and to be complementary to, the normal
theater system. This component, called Veritone, remains in the
circuit permanently, forming part of the overall loudspeaker system. Because
these frequencies are non-directional, only one Veritone system is required
regardless of the number of audio channels in the theater. It has been found to
bring out the low end of older sound recordings, as well as to produce a
sensation of "feeling" when the tracks are appropriately dubbed.
When the earthquake sequences of San Francisco were played through a
Veritone installation at the SMPTE Conference in the Academy of Motion Picture
Arts and Sciences Theater, the auditorium literally shook.
Sound Recording Negative Materials.
The sound recording negative in general use in the U.S.A. is the Eastman
fine grain sound recording film 5375. Its high-frequency resolution is
limited. Another black-and-white negative that has a resolving power almost an
order of magnitude greater is the Eastman high-contrast panchromatic film
5369. Doubts were expressed concerning its capability of exhibiting
satisfactory sound-recording image spread so as to yield a good print with low crossmodulation
performance. Initial tests gave very encouraging results, and further
thorough evaluation proved that 5369 yields a vastly superior high-frequency
recording, Figure 23 shows comparative data for these two types of
sound-recording films together with data for three others, Using a normal-speed
contact printer, 20 kHz was well and consistently reproduced from a 5369
negative. As a rule of thumb, this material should be used when it is desired
to have a good high-end response beyond 10 kHz and when the added negative cost
can be justified. Measurements on a Westrex RA 1 251 reproducer gave a 6-dB
improvement at 1 5 kHz with this material. It has a panchromatic emulsion and
a clear base and requires handling in complete darkness. The clear base calls
for an adjustment in the printing filter pack due to its increased transmittance
over the normal gray base.
Colortek optical stereophonic sound film system offers a novel approach to
four-track variable-area recording and applies CCD video technology to the
readout of the soundtrack, within a totally integrated sound system. Although a
small modification of the projector sound head is required to realize the full
potential of this system, the increase in sound quality and performance and the
economics inherent in a single-print-type inventory will justify the change.
The progress realized with this system should satisfy, it is hoped, sound
reproduction requirements for years to come. The technique can be extended to
the 16mm and super 8mm formats.
and organizations, too numerous to be listed in full, have contributed by lending
equipment and facilities and by their invaluable advice and comments to the
development of this new sound reproduction technology. To all of them the
authors wish to express their sincere thanks, especially to the Academy of
Motion Picture Arts and Sciences, the Burbank Studios, the Christie Electric
Company, Consolidated Film Industries. DeLuxe General Laboratories, Metro-Goldwyn-Mayer,
20th Century Fox. United Artists and Westrex.
1. John Mosely, "Quintaphonic Sound,"' SMPTEJ. 86, 20-29, Jan. 1977.
2. John G. Frayne, "A Compatible Photographic Stereophonic Sound System," J. SMPTE. 64,
303-308, June 1955.
3. "A Comparison of Tlhe Attack Behavior of Telcom, dbx, and Dolby A." Wermuth
and Senf.AEG Telefunken. July 1976.