All sources – basically up to the introduction of digital television transmission – had the recurrence frequency of their waveform generators locked to a common reference, which was the mans supply frequency, but the relative phase of their sync waveforms was random. Sources which are not in time coincidence at the mixing point are termed “non-ssynch ronous ” and can only be switched by cutting or fading to black. The alternative is to ensure that the signals are time-synchronous at the mixing point, to avoid roll-over and other objectionable effects.
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A Brief Survey of Source Synchronisation |
Various methods of achieving source synchonisation at the mixing point are discusssed, including Slavelock and Genlock, and, indeed, the use of standards conversion to provide synchronous sources
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