H - Electricity – 03 – G
Patent
H - Electricity
03
G
352/32.5
H03G 1/04 (2006.01) G11B 7/06 (1980.01)
Patent
CA 1163017
APPARATUS AND METHOD FOR DETECTING CROSSMODULATION DISTORTION ABSTRACT A method and apparatus for detecting crossmodulation distortion on an optical sound track by detecting variations in the light transmitted through at least one predetermined area on the sound track, the predetermined areas being selected such that their transmittance varies substantially only with the amount of crossmodulation distortion on the sound track. The predetermined areas preferably have dimen- sions along the sound track which are a whole number multiple of, and substantially greater than, the wavelength of a high frequency test signal. Light is also transmitted through at least one second predetermined area on the sound track which clip the high frequency test signal, thereby providing a low frequency phase reference for determining the relative exposure of the film. In an alternate embodiment, the predeter- mined areas are divided into primary and secondary areas, mutually spaced by a distance which is out-of-phase with respect to the wavelength of a low frequency test signal. Crossmodulation distortion information is obtained by comparing the light transmitted through both areas. Instead of single predetermined areas, multiple areas spaced by whole number multiples of the low frequency signal wavelength can he used to improve the resolution of the system's frequency response. A mask with defined apertures controls the light paths. Testing for crossmodulation distortion can he done by simply moving the film by hand a short distance through the test equipment. Because crossmodulation is continously monitored, diagnostic testing is also possible.
375526
Beard Terry D.
Smart & Biggar
LandOfFree
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