Abstract: Each of the video signals to be combined to create the special effect is applied to the first input of the corresponding one of a plurality of mixing units. The outputs of the mixing units are connected in common. Each mixing unit has a second input. The synchronization and burst signals of one of the video signals is applied to the second input of one of the mixing units. The gain of each mixing unit relative to the applied signal at the first input varies as a function of a corresponding control signal. Each control signal has an amplitude varying directly with the amplitude of an externally applied input signal and inversely with the amplitude of the next following input signal.

Abstract: For phase matching a first and second television signal, both signals are applied to the inputs of an electronic switching circuit, whose output is connected to a standard television monitor. The switching circuit applies the video portion of the first television signal to the monitor. For matching the phase of the synchronizing signals, the synchronizing signals from the first television signal are applied to the monitor for the first half of each field, those from the second television signal during the second half of each field. A visually detectable shift occurs between the top and bottom half of the picture displayed on the monitor if the synchronizing signals of the second television signal are not in phase with those of the first television signal.