| 摘要 |
Apparatus for deriving a television quality parameter from an insertion test signal line which is repeated at regular intervals during field blanking periods of a television signal comprises a sampling system operable, when actuated, to provide a digital amplitude signal representing the instantaneous amplitude of the test line, controllable actuating means for actuating the sampling system, a computer programed (a) to calculate the quality parameter from a plurality of digital amplitude signals, corresponding with different sampling positions on the test line, and provided by the sampling system, (b) to provide the calculated quality parameter as output, (c) to respond to timing origins carried by the television signal and control the actuating means at times, so related to the timing origins, that the signals of said plurality of signals are provided in turn, at a low average rate, e.g. each from a different occurrence of the test line. A relatively cheap analog to digital converter may be employed.
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