Methods
Implicit in the idea of time base correction is that there must be some target time base that the corrector is aiming for. There are two time bases commonly used. The first method is to make the frames, fields and lines come out smoothly and uniformly, at the rates specified by the standards using an oscillator for time reference. The alternative to this method is to align the frames, fields, and lines with some external signal, a procedure called genlocking. Genlocking allows sources that are not themselves genlock-capable to be used with production switchers and A/B roll editing equipment. Stand-alone broadcast model time base correctors typically will genlock the signal to an external sync reference, and also allow the brightness, contrast, chrominance, and color phase ("tint" or "hue") to be adjusted.
Some TBCs featured a Drop Out Compensation (DOC) circuit that enabled videotape flaws caused by oxide drop-out to be temporarily corrected. The DOC circuit required dedicated cabling between the videotape player and the TBC in which irregularities were detected in portions of the video image. Previously captured and stored lines of video would then be superimposed over the flawed video lines.
A variant of the time base corrector is the frame synchronizer which allows devices that cannot be "steered" by an advanced sync signal to also be time base corrected and/or timed into a system. Satellites, microwave transmitters and other broadcast signals as well as consumer VTRs cannot be sent an advance sync signal. A frame synchronizer stores at least a full frame of video. If the buffer over or under fills, the Frame Sync will hold the last good frame of video until another full frame's worth of video is received. Usually this is undetectable to viewers.
Read more about this topic: Time Base Correction
Famous quotes containing the word methods:
“We are lonesome animals. We spend all our life trying to be less lonesome. One of our ancient methods is to tell a story begging the listener to say—and to feel—”Yes, that’s the way it is, or at least that’s the way I feel it. You’re not as alone as you thought.””
—John Steinbeck (1902–1968)
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—Herbert Hoover (1874–1964)
“The comparison between Coleridge and Johnson is obvious in so far as each held sway chiefly by the power of his tongue. The difference between their methods is so marked that it is tempting, but also unnecessary, to judge one to be inferior to the other. Johnson was robust, combative, and concrete; Coleridge was the opposite. The contrast was perhaps in his mind when he said of Johnson: “his bow-wow manner must have had a good deal to do with the effect produced.””
—Virginia Woolf (1882–1941)