UPDATE: This post has been updated to this post:
What is a TBC? Time Base Correction for Videotapes
Consider reading that newer version of this post, if you found this page through a link or search engine.
Direct link to new TBC article:
http://www.digitalFAQ.com/forum/show...base-2251.html
Thanks,
-LS
`````````````````````````````````````````````````` `````````````
I don't really want to get too in-depth on this question right now, as I'm collaborating on an article about this very topic. I'm actually going to steal a little of it to write this quick reply:
A TBC is a timebase corrector. By the most basic definition, video is input into a buffer, and then it is corrected before being output again. However, the term "TBC" is often used so loosely, that it seems any type of "correction" can apply. There is no universal or standardized definition, so product makers can get away with calling anything a TBC. Sometimes I wonder if my toaster has a TBC. The best way to define a TBC is by empircal analysis of devices that exist, and claim to have a TBC inside, and analyzing what they do.
Standalone Full-Frame TBC:
A good recent-era standalone TBC will
- reduce visual on-screen image jitter (up.down image bounce)
- overwrite "dirty" signal areas with new clean ones --- these areas often used by anti-copy, which of course is an artificial video error -- this is not going to visually improve the signal, it would only prevent image quality issues caused by false detection of anti-copy, such as Macrovision
- and provide a steady signal that prevents dropped frames on capture cards, or pre-mature recording stop on DVD recorders
A standalone TBC will generally not clean up visual image quality, such as removing chroma noise or suppressing visual distortions (excluding jitter)
Good standalone TBCs include
You would do best to avoid old user TBCs found on eBay and other places -- many ancient 80s/90s TBCs work different than the ones specifically suggested here.
S-VHS VCR Line TBC:
Unlike the standalone TBC, this one will
- NOT give a continual clean signal out from the VCR
- NOT remove anti-copy signals, by replacing those often-dirty areas with new clean data
- NOT help much with jitter -- in fact it can sometimes increase the amount of jitter
What it will do, however, is clean the visual quality, by:
- removing or reducing chroma noise (the red/blue colored mist found in all VHS tape formats)
- removing geometric distortions from the image, such as the wiggling appearance of older video, as if viewed through a rippling pond or bathtub
Very often VCR TBCs are merged with embedded noise reduction circuits, which use the power of the TBC to further suppress or remove grain and prevent color bleeding. The quality of the TBC really depends on the model and line/series of the deck. In many cases, the oldest "professional" VCRs (used in studios and hospitals) are worthless crap, as compared to late 90s and early 2000s professional and prosumer models that work much better.
DVD Recorder "TBC":
This is where we start to enter the land of "it's a TBC because we wrote it on the box". In many cases, the "TBC" is nothing more than a basic frame sychronizer, or circuitry that provides a similar function. These tend to only be good at one thing: removing "flagging" or "tearing" that can sometimes be seen on the top of a VHS signal, a visual distortion on screen. You'll have to disable the VCR TBC and often remove the standalone TBC, to get benefit of this feature, as needed.
NOTE: These DVD recorders often have bad capture/recording quality, unfortunately, so you'll want to use it in "passthrough" mode. This means you feed a signal into the DVD recorder, and then output it to a better capture device further on. It is not used for recording. You can often re-add the standalone TBC after the DVD recorder, because it's still not necessarily the best analog signal yet.
The Panasonic "ES" series from 2005-2006 is known for this (ES10, ES15, etc).
DVD recorder "TBCs" will do next to nothing (or outright nothing) in terms of visual OR signal cleaning. Some of the DVD recorders do have digital NR, but it can be overly strong. The ES10, for example, over-processed the video with NR engaged, causing temporal blurring and posterizing/banding the video (compressed color palette).
DV Converter Box "TBC":
Even worse than the DVD recorders, these TBCs generally don't do squat.
- In some cases, these will act like the DVD recorder frame synchonizers, very mildly correcting the input signal stability, just good enough to be captured without dropped frames.
- In other cases, it does nothing.
Conclusion...
The best advice is to stack a good S-VHS VCR with a TBC with a standalone TBC, to take care of both image/visual AND signal quality. If you use a DVD recorder or DV box further down the line, so what -- forget it has a TBC. Or rather, forget "TBC" was written on the box.
Also...
If this information has been helpful, please
upgrade to a Premium Member status. Premium Members will get longer in-depth one-on-one help for their projects, and in the future will be able to access exclusive content. And the price is about the same as buying a book or couple of magazines -- but far more useful!
Thanks.
