So what’s a timebase corrector, what’s a frame synchronizer, what’s the difference, and why do you care?
Okay, let’s begin by going back in time a little bit. Up until the late 1970s, this was, by and large, the only kind of videotape recorder there was. A 2″ quad machine. It recorded video by an ingenious method. Four recording heads were mounted, 90 degrees apart, on this wheel which rotated at high speed – 14,400 RPM. A 2 inch wide piece of videotape was pulled past these heads at 15 inches per second, and a series of video tracks were laid down on the tape. You needed 32 tracks for one full frame of video. You can see the segments here on this video playback from a quad machine. Now, when you played back this tape, there would be some small mechanical errors. This meant that the image off the videotape wasn’t stable – it weaved back and forth a little bit. By using two devices – an AMTEC, and, when colour video recording was invented, a COLORTEC – a stable image could finally come out of the
machine and you could then used to play back images during live teleproduction. The AMTEC and COLORTEC were, in essence, the first timebase correctors. They corrected the small mechanical timing errors in videotape playback. Next, we had helical scan VTRs. One field was recorded during one rotation of the head. The segments were gone, but we still had timebase error when playing back a tape. Helical scan recording was the basis for all videotape recorders, including home VHS.
But at this point you may be saying, “I played back VHS tapes on my TV set all the time, and I didn’t need a timebase corrector to do it.” That’s because your TV set was able to compensate for the small
mechanical fluctuations. Basically it wasn’t too picky about
these errors. But this is how much timebase error is actually in a home VHS machine. Pretty nasty. So, to play back helical scan VTRs in a broadcast environment, we still needed the time base corrector. Here’s an early one – it took up a large amount of space in an equipment rack, and couldn’t even correct a full field of video. It could only store in computer memory a few lines of video. But it worked. It took the original shaky video, stored it in memory, and then played out those few lines in perfect synchronization so that the rest to the broadcast
equipment could use the now stable video. When we started to use satellites and microwave links to beam back signals to television stations, a better solution was required. Because those signals are so far off time from the station, we need to store entire frame a video in
memory then release it when we were ready to integrate that frame into a television production switcher, for example. This box was called a framestore, or frame synchronizer.
Because we could store so much video information in these boxes, they often had the ability to correct timebase error from videotape machines, too. Eventually, all frame synchronizers could do this, and we called them timebase corrector / frame synchronizer, or TBC / Frame Syncs for short. if you’re still using analog video in
your production center you probably don’t have a dedicated TBC anymore. you’re probably using a TBC frame sync
to correct incoming videotape playbacks as well as external feeds like satellite
receivers, microwave feeds, and even things like DVD players. Storing a whole frame at once solves a multitude of problems.
So, that’s the difference between all these boxes. A TBC only corrects timebase errors off videotape machines. A frame sync stores an entire frame, and modern versions of a framesync also do timebase correction as well.