A synchronization pulse detector for detecting a synchronization pulse within an input signal. The input signal has “level” portions (i.e., substantially non-time varying portions) and “transition” portions (i.e., substantially time varying portions). The pulse detector includes a pulse shape detector for determining each time the input signal has a sequence of a first “level” portion, followed by a first “transition” portion, followed by a second “level” portion, followed by a second “transition” portion followed by a third “level” portion, one of the first and second “transition” portions being positive and the other one of the first and second “transition” portions being negative. Each time such sequence is determined a pulse_shape detected pulse is produced. An evaluator is provided to reject invalid pulse_shape detected pulses. In one embodiment, the input signal is a video signal and the evaluator includes a time window for determining whether such shape_detected pulses are produced at a predetermined rate expected for the series of synchronization pulses. The evaluator includes a voltage window responsive to the produced shape_detected pulses and their associated values of the second “level” portions for determining whether one of such produced second “level” portions is substantially the same as or lower but not higher than the lowest DC value recorded during the time-equivalent of one line of video. The evaluator may include both the time window and the voltage window. The voltage window is mainly used to acquire an initial lock to an unknown and not yet clamped video signal.