How to test time base correctors? (TBCs)

[Eagleaye]

Does anyone have any suggestions on how to test time base correctors to judge whether they are performing as expected? Do TBCs either work or not, or are there varying degrees of performance.

Is there a way of "tripping them up", creating artificial conditions that they should be able to cope with, or is the only way of assessment by comparing captures with and without a tbc?

[NJRoadfan]

You need a test tape that has the errors on it that a TBC is supposed to correct. Something with a lot of horizontal jitter, some flagging, and some vertical bouncing. A good TBC should noticeably clear up the horizontal jitter and the flagging. If the unit claims to have dropout compensation, you need a damaged tape with dropouts to see what it really does.

To test the unit's transparency (does it muck up the color and brightness levels?), you need more equipment. Professional studios relay on a vectorscope to check color, and a waveform monitor to check brightness. A test pattern generator is used to create the reference video to feed into the TBC. Software versions of the scopes exist and do an OK job and have the price of free.

I wouldn't use them for serious adjustment though, just to check to see if the equipment is really screwing up your video as some old worn out rack mount TBCs are known to do. A DVD with test patterns can be used as a reference. The AVT-8710 also has a built in color bar generator.

I posted some articles on the subject here: http://www.digitalfaq.com/forum/vide...rate-ntsc.html

[lordsmurf]

Quote:

Originally Posted by NJRoadfan

You need a test tape that has the errors on it that a TBC is supposed to correct. Something with a lot of horizontal jitter, some flagging, and some vertical bouncing.

... and some "copy protection" (anti-copy). Several types, especially the problem ones. Normal Macrovision usually isn't the issue.

Quote:

Professional studios relay on a vectorscope to check color, and a waveform monitor to check brightness. A test pattern generator is used to create the reference video to feed into the TBC.

You'd be surprised how many don't do it these days. Even "eyeballing it" is sometimes not done. So sad. I did work with one company where the guy often said "what's that" when talking shop. Was I working with pros, or was this a college kid in his intro class? (It was the former. Rhetorical question.)

You can always tell when work is butchered, and it happens quite often these days, especially at local TV stations and small cable channels. For example, GSN (Gameshow Network) has screwed a lot of stuff up lately. I just change the channel -- I'm not watching that fubar crap. Levels, audio, and aspect ratios are all messed up on a regular basis.

[Eagleaye]

Thanks NJRoadfan, would flicking through channels or bringing up the VCR menu while capturing give any indication of performance?

Thanks Lordsmurf, so if a "macrovisioned" tape can be captured the tbc is good? Do tbcs either work or not?

[lordsmurf]

Flicking the channel, no. You need a constant.
The VCR menu, yes. It's one test. You should do several tests, however.

[NJRoadfan]

Quote:

Originally Posted by lordsmurf

You can always tell when work is butchered, and it happens quite often these days, especially at local TV stations and small cable channels.

My high school's TV studio was like that, but I didn't know any better and the teacher wasn't technically minded. If I recall, there was a scope somewhere that could have been used. Luckily the tapes I have from those days are easily fixed since the cameras were manually white balanced and the lighting is consistent. The most it takes is a twist of the hue adjustment to fix those videos. The problem was up the chain from the cameras, the Knox Studio 40 character generator was responsible for the color shift!