Colorburst

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Colorburst is a signal used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the beginning of each scan line, a television receiver is able to restore the suppressed carrier of the chrominance signals, and in turn decode the color information.

[edit] Explanation

In NTSC, its frequency is 39375/11 kHz or 3579545 Hz with a phase of 180°, whereas PAL uses a frequency of 4.19 MHz, with its phase alternating between 135° and 225° from line to line. SECAM is unique in not having a colorburst signal, since the chrominance signals are encoded using FM rather than QAM, making synchronization irrelevant.

Since the colorburst signal has a known amplitude, it is sometimes used as a reference level when compensating for amplitude variations in the overall signal.

[edit] Crystals

Because color televisions are so common, colorburst crystals (which actually operate at four times the colorburst frequency, 157.5/11 MHz or 14.318 MHz) are widely available and often found in various other applications. For instance, the original IBM Personal Computer's 4.77 MHz processor clock was one third of a colorburst crystal, and the Commodore Amiga's 7.16 MHz clock was one half. The 8253 interval timer frequency in all PCs is still standardized at 1/3 of the colorburst frequency, 13125/11 kHz = 1193182 Hz.