The Colortek Optical Stereophonic Sound Film System
Colortek is an optical sound system rendering four separate unilateral variable-area audio tracks and a central control track, all within the area of the present monophonic variable-area and variable-density soundtrack location as defined by American National Standard PH22.40–1967. The innovative design of the system employs, as a sound reader, a charge-coupled-device scanner (CCD scanner) and applies video technology to the read-out of soundtracks. It scans the four soundtracks transversally at 10 MHz, resulting in a CCD frame rate of 40 kHz, as the tracks pass longitudinally at the normal speed of 24 film frames/s (457.2 mm/s) through the sound reader. The electronic drive of a Westrex light valve has been modified to obtain the new soundtrack configuration. No ground-noise-reduction device or circuit has been incorporated, because the design of the CCD scanner suppresses ground noise almost completely. The soundtrack may also be reproduced on projectors with a normal optical soundhead. However, due to the use of electronic companding and to the lack of ground-noise suppression, the reproducing electronics should be modified to reproduce the four-track format correctly. This format can be reproduced monophonically as well as stereophonically. Both the frequency and dynamic ranges of the recording light valve have been extended to achieve faithful transfer from the magnetic to the photographic printing medium and faithful reproduction in the theater. By the use of matrix encoding, the system can be extended to accommodate six separate channels of sound for surround sound effects in 35mm theatrical presentation. The narrow center control track serves several purposes: (1) it enables the CCD scanner to recognize and compensate automatically for any side weave of the soundtrack; (2) it serves as an image-spread monitor for correcting, within limits, distortions caused by image spread; (3) it can be used to trigger special sound effects or auditorium speaker groups as encoded on the control track; (4) it also can be used for automatized general theater operation. A specially designed compander completes the system.
- Print ISSN
- 0036-1682
- Published
- 1978-04
- Content type
- Original Research
- DOI
- 10.5594/J17389