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Color Test Descriptions (Chromalluma Delay Inequality. Differential Gain, Differential Phase)
Differential Gain Test
The differential gain test measures the change in amplitude of the
Description
chrominance subcarrier as the luminance changes from a blanking level
towards white level. The five-step riser portion of the test signal is used to
perform this measurement. The test signal is automatically selected.
A fast fourier transform is performed on the reference burst and each step in
the five-step riser. Each step is normalized to the reference burst. Averaging
is employed to minimize noise contribution to the reading.
The peak-to-peak amplitude of the largest riser step is found. Then, the
riser step with the smallest peak-to-peak amplitude is found. The difference
between the two amplitudes is computed and expressed as a percentage of
the largest amplitude. Differential gain calculation where max = largest
packet value in % and min = smallest packet value in % follows:
If 5th PKT YES NO is set NO, then the calculation is based on the first
four steps in the five-step riser in channel measurement mode. The 5th
packet is always used in system measurement mode. The MORE INFO
measurements.
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Test Descriptions
8-37
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