TBC for the desperate?

[latreche34]

That's all there is to it, a frame TBC should be transparent it should not do anything else other than taking that black wavy vertical stripe and turn it into a perfectly straight line, So this test is all that is needed. Note that the MX-1 has two TBC levels, One is consumer level that makes the VBI bar just good enough for a stable picture which you see in all consumer level TBC's and the other is broadcast standard (FCC standard as he called it) that turns the VBI into a perfectly straight line, Which I didn't know it could be achieved on a device like that until I watched that video, I've seen this feature so far on only pro devices such as the S&W TBS800 I have which I posted test captures over at VH.

[dpalomaki]

It boils down to picking the right tool for the job.

There are a lot of different types of hammers. I wouldn't use a framing hammer for trim work, or a tack hammer for framing construction.

I think the point is that the favored (on this site anyway) TBCs tend to do well with the broad range of typical VHS signal garbage. Other products may or may not cope with the same range of issues. If a product work for one's case to one's satisfaction, that is what matters. It may be appropriate to have several variations of a tool in the tool kit.

[BW37]

I've been following this thread (as I do most just to learn) and I've decided to speak up on this overall subject.

I would very much like to see a list of the specific problems that frame TBCs fix and then an accompanying list of which of these problems specific TBCs and "TBCish's" fix or don't fix. Lots of vague pros and cons are thrown around and all but a very limited number of TBC's are pooh-poohed as useless or praised as a godsend. But there is rarely any real explanation of why. From my perspective, terms like "weak", "strong" or "crippled" don't mean anything without definition.

My perception is that some TBCish devices (by that I include all possible TBC candidates) are "robust" and work to rebuild a reliable frame signal for almost any crap signal they are sent. Other TBCish devices are not that robust but still might do enough to get the job done for many but not all tapes (some DVD recorders for example). For many of us, many (or most) tapes might be adequate. For others not. Certainly for anyone that makes a living (or even side income) doing captures for others, robustness under all conditions would seem essential. There also seem to be significant differences between NTSC and PAL options, both for better and worse.

A specific function that I believe a "robust" (strong?) TBC will do is to ignore Macrovision and rebuild a solid frame signal when sent an intentionally bad one (Macrovision). If you are trying to digitize a library of commercial tapes this would be essential. If you are digitizing a bunch of home videos maybe it is not essential, though desirable. I have a number of devices that simply refuse to pass (or record) a Macrovision signal. When they sense it, they just give an error message or shut down the signal. For instance, my DV camcorders record for a instant and then stop recording and put the error message on screen. I've used this "feature" to test the Macrovision "passability" of a few TBCish devices. I have a few that will defeat the Macrovision and others (that I know have a "frame synch" function) but won't pass a Macrovision signal (e.g. Panasonic AG-MX70). It's fun to play with the "transitions" on the MX-70 to test when it decides it's seeing enough of the Macro signal to shut down the output. It won't let much through... But my bet is that it will correct weak frame signals as long as they are not so weak as to be perceived as Macrovision (false Macrovision?). We'll see. BTW, you don't want an MX-70 unless you have a very large space to put it. It's a monster...

So can we get some definition of what makes a good TBC? My gut tells me that they are actually much like capture devices and VCR's: they vary from bad, to OK, to good, to better and finally best. And Like VCR's, condition will be crucial as well.

BW

PS: Like Barry, I'm now taking cover

[latreche34]

Very legitimate questions deserve honest answers, While I cannot answer all of them let me make a distinction between frame time base correction and Microvision removal.

A frame TBC's main function as I described above is to take the VBI signal and re-align it to an internal clock reference producing a clean signal for the device down stream to lock on, this type of time base correction is found in any TBC as well as old school TV's, In addition frame TBC's have a digital frame store, so besides fixing the sync signal it actually store the whole frame or a field into a volatile memory by digitizing it first and letting it go at a steady pace so that you would have a perfect and clean video. There is another type called frame synchronization that actually takes the stored frames and the digitized audio and time them together into one signal, this feature cannot be found in TBC's that has video inputs only like the AVTool and TBC1000.

A Macrovision removal is another feature the TBC can or cannot/may not have based on the design at the time and the jurisdictions where it's sold or made and their laws, Once you look into how MV works you will notice that it has nothing to do with VBI or frame timing, It is a form of gain control manipulation. Unlike modern VCR's and capture cards, TV's and old VCR's and devices that ignore or has the MV removal capability don't get their gain control calibration from the infected section of the VBI, They either generate their own levels or get the calibration levels from different sections of the VBI section that sits on the top of the frame, I don't know exactly the specific designs but I know there are many and results may differ from one design to another, They were never released to the public as far as I know.

Another great function of a TBC that rarely get mentioned is the chroma sync, The chroma burst signal that follows the HBI signal on every scan line can lead to chroma shift or artifacts if the signal is weak, both line TBC and frame TBC can fix certain types of chroma artifacts, for instance line TBC can address chroma shift, frame TBC can address green and pink chroma stripe on top of the frame.

This is a really complicated subject and not a lot of old school engineers are around to expand on it, We can only judge by experimenting ourselves and see what works and what doesn't

[lordsmurf]

"Macrovision removal" isn't a thing. For starters, Macrovision is merely one brand of anti-copy, and multiples existed. Furthermore, Macrovision branded anti-copy had multiple versions and variations over the years. Anti-copy is nothing more than the injection of artificial video errors into a signal, and really has no place in a TBC conversation. Simply realize that the artificial junk signal is corrected and/or effectively removed from proper TBC, as is a natural error.

But also realize this applies to TBCs that are designed for chaotic consumer sources, not units designed for cleaner sources. Those usually-"pro" units actually filter on less signal vectors, and/or in a weaker manner. This is why any old "TBC" isn't a useful TBC for our consumer analog video capture needs. The same applies to TBCs (or "TBCs" aka not really) built into other items, the "also does TBC" type function found in mixers/etc. Those TBC functions existed not to clean the tape signal, but merely to assist the unit with its internal operations. This is an important distinction to make, as it almost always affects the power/weakness of those units. It's why, for example, DataVideo DVK chroma keyers aren't really TBCs. The TBC function is buried within the other internal operations, and was only made strong enough for those operations. Imperfect input sources easily trip it up, which is why a Panasonic DVD recorder should be used as a pre-filter (and the ES10/15 itself has shaky frame/signal output, even if strongly line corrected).

I have some very telling examples of all this, but it's currently being curated.

Frame TBCs really do nothing for chroma. Not shift/bleed, not cNR -- I wish! Bad chroma has always been a pet peeve. I hate an image that looks like it was infested by a red/blue swam of bugs. Chroma fixes are largely a byproduct of line TBC, and it's further pushed more effective due to digital NR (DNR) in S-VHS VCRs.

It is a complex topic.

[RobustReviews]

Quote:

Originally Posted by lordsmurf

"
But also realize this applies to TBCs that are designed for chaotic consumer sources, not units designed for cleaner sources.

Are you absolutely certain you want to nail down that domestic video (designed to be replayed without a TBC) is 'more chaotic' than professional analogue formats?

How much work have you done with UMatic and C?

[lordsmurf]

Quote:

Originally Posted by RobustReviews

Are you absolutely certain you want to nail down that domestic video (designed to be replayed without a TBC) is 'more chaotic' than professional analogue formats?
How much work have you done with UMatic and C?

While U-matic is probably as dirty a sources as VHS, being from the 1970s, it's not the same. And it's why I specifically type "consumer analog sources", meaning not U-matic, which was a broadcaster format. Different issues to contend with. Several members here are more versed in U-matic than both you and I (even adding up our knowledge and experiences).

Remember, this site is used by professionals of all ilk. Quite a few TV station employees here, Apple employees (iTunes), retired broadcast engineers, etc. Many choose to read, not post, but we PM and email. Remember, I worked for studios before health sidelined me some years ago. Lots of filmmakers, actors, etc. While this site has a good posting community, the non-posting community is impressive. I've seen some names (verifiable, it's them) that make me halt what I'm doing, and say "whoa".

High-level discussions (like TBCs) happen on the backend, too, not just the posting frontend. Though I do all I can do encourage posting, sometimes requiring it for me to answer questions. There's been a few times where somebody important was treated a wee bit harsh by a regular member, and it made me cringe, had to apologize for the regular more than once ("he means well, good info, he may have had a bad day").

Always keep this in mind. You're being watched, even if you don't know it. The entire reason I worked for studio is because I was headhunted,

[latreche34]

Chroma does have timing, It doesn't just stick to the luma like a magnet, it has to be timed precisely, TBC's process both chroma and luma timing. Yes DNR's function is to clean the chroma stains but those are visual artifacts not part of the chroma timing signal.