| 摘要 |
<p>A method and apparatus for generating an artificial vertical sync pulse for controlling the scanning drum (14) servo of helical wrap magnetic video tape (12) recording and reproducing machine. The artificial vertical sync pulse is less susceptible of experiencing timing errors relative to control track signals caused by tape expansion or contraction because it is physically much closer to the control track head than the conventional vertical sync signal that is normally used to control the scanning drum servo. A component (11) of the beginning portion of the vertical synchronizing signals that is physically present on one side of the drop-out area (30) is detected and this component triggers a counter which opens a window (31) for detecting a particular horizontal sync pulse that is physically close to the control track head (46) and the horizontal sync pulse defines the artificial vertical sync pulse. </p> |
