Prior to the availability of digital video mixers, any two video sources mixed together through a
video switcher had to be synchronously matched by using a time-base corrector if the video source was a playback VCR or a
genlock-able camera if the video source was a live camera. It was necessary to match the scan rate of these video sources
so that the transition took place during the vertical interval blanking period, the analog “non picture” that takes place
between video fields. As you might have guessed, this was a very expensive process considering that you needed a TBC for
each playback VCR and mid to high-end video cameras with genlocking capabilities.
When digital video mixers came into the picture, no pun intended, any non-synchronized video source could be plugged in and mixed, wiped or keyed with another non-synchronized video source (i.e. consumer VCRs and camcorders, laser-disk players, TV tuners, NTSC computer outputs).
A frame synchronizer literally takes a digital “snapshot” of each incoming frame of video and releases immediately as the next frame comes in. Once converted to the digital world, the video frame can be blended with any other digitized video frame via transitional effects.
Now, how does the frame synchronizer in your digital mixer differ from an actual time-base corrector? They both work on the principle of converting incoming video from analog to digital. And they both stabilize the video picture so that their respective outputs can feed other equipment requiring digitally-stable signals, such as the NewTek Video Toaster.
A time-base corrector, or TBC does one job: It corrects inconsistencies of an analog playback VCR. It accomplishes this by sampling one video scan line at a time (not an entire frame), corrects any instability by stripping the scan line of it’s old sync signal and replacing it with a brand new sync signal created by the TBC’s own built-in precise timing clock. Modern day TBCs, with their vast digital memory, can correct up to an entire field (262.5 scan lines) of incoming video. These are known as “infinite window” TBCs (obviously more effective than the two line correction capability of some “TBCs” built into high-end consumer VCRs).
The frame synchronizer, on the other hand, digitally synchronizes two separate video sources without necessarily correcting them.
There are some TBCs that have built-in frame synchronizers and there are frame synchronizers with built-in TBCs (i.e. Videonics MX-1). However, they are still two different creatures performing similar jobs.
Due to the digital video mixer’s ability to feed the Video Toaster a myth began that the Panasonic digital mixers have “secret” or “hidden” time-base correctors built in to them. The only thing a Video Toaster requires from an input is that it is digitally stabilized. And both TBCs and frame synchronizers accomplish that task. (Plus, as competitive as the digital mixer manufacturers are, if one of their digital mixers had a built-in TBC, the consumer would be the first to know about it.)