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Response to Purpose of Color Bars...

from Ken Smith (mstarmedia@juno.com)
The purpose of color bars on the head of each and every tape is so that the machine that plays it back either in editing or on air can be set for standard playback. It is possible that head wear, mis- alignment and so forth, can cause poor recording. By playing back the bars, weather SMPTE, split field, or single field, doesn't matter, and then adjusting the proc amp controls on the play back machine, using scopes it can be set to bring a sub-standard recording back to standard playback. When set up right, we can do match frame edits using different brand machines in different edit facilities. The key is the bars.

The standard in the broadcast industry is one minute of bars recorded at the head of field tapes. In addition to providing enough bars for propper playback setup, this also guarantees enough leader before good footage. If there is any manufactured defects on the tape, they will probably be in the first or last 30 seconds where the tape was cut to squeeze into the shell. Also, this guarantees more than enough leader for pre-roll. On the master, the industry standard, as noted in the International Teleproduction Society Handbook of Recommended Standards and Procedures, is 10 feet of blank leader (that probably works out to 20 or 30 seconds on most tape formats), 60 seconds of color bars with 1,000 kHz audio tone, 10 seconds of slate and at least 1.8 seconds of black before the program starts. In our facility, which produces network programs among other productions, we include 10 seconds of black between bars and slate and another 10 between slate and program. In my former life I worked in the tape room of a large market TV station and also switched air. Lots of leader and lots of bars and tone always made me happy!

Ken Smith Morning Star Media Group e-mail: mstarmedia@juno.com on the web: www.morningstartv.com (check us out)

(posted 9210 days ago)

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