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Video Recording

Frequency Modulation

The wide bandwidth of a video signal poses a problem, due to the way that the inductive impedance of the recording head (i.e., resistance of the recording head to rapid changes in current flow) rises with the increase in the frequency. For normal recording a thousand times more head voltage will be required for a 5-MHz signal than for a 30-Hz signal. To avoid this problem, the wide-width luminance (brightness) signal is not recorded directly, but is instead recorded using a process called frequency modulation (FM), where the original signal is used to modulate (vary) the frequency of a high-frequency carrier signal. This effectively increases the ratio of the lowest and highest frequencies but does not reduce the bandwidth. FM signals give a better signal-to-noise performance and are less sensitive to unwanted interference.

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