X75 TBC proc amp calibration, VHS alignment tape?

[Angies_Husband]

Hi,

Just starting to get the first captures of my workflow in, and I have a question around properly calibrating my VCR output.

I like the philosophy laid out in previous posts where you first calibrate with tools, then calibrate and fine tune by eye. Makes total sense.

However, I am not entirely sure how to generate the "source" from the VCR, if I don't have an alignment tape (e.g., something with SMPTE bars)... Also, let's just assume, hypothetically, that I have a waveform monitor and vectorscope... (different issue!)

My TBC is a Leitch X75SD (similar to the DPS 575 I think), and it has a test signal generator (TSG) option to output bars and such... Would it be valid to output Bars from the X75 to the VCR, record it to tape, and then playback the tape to do the initial proc amp calibration? (it doesn't seem valid, but I am new to this...)

Are there other options?

Many thanks!

My workflow is:
Mitsubishi HS-HD2000U ----[SVIDEO]----> Leitch X75SD TBC ----[SDI]----> AJA LHe PCIe card (legacy) -----> AJA Machina SW

[dpalomaki]

Your proposal to record bars would make sense if you are about to record with that VCR. But it may not give valid results for playback of material recorded on another machine. If the TBC bars are good, use them to check and if necessary adjust everything down stream from the point where you connect the VCR.

With everything calibrated downstream, you can use commercial recordings to "eyeball" the quality of VCR's output for problems. Commercial tape playback should remain legal on the waveform and vector displays. Bright whites shoud hit around 100 IRE, and blacks around 7.5 IRE (for USA NTSC).

[lordsmurf]

I'm not fond of generated calibration bars because those may not actually be calibrated, especially mid-workflow gear. You need to calibrate from the 1st device through the last, not just the middle. Some give no means to adjust calibration anyway, so it becomes moot.

I'm not a fan of that TBC ... but with TBCs getting more scarce, I guess it's not always easy to choose an ideal unit. Essentially I'd trust color bar generated by it even less than normal.

The biggest issue is calibrating the viewing computer monitor, and just eyeballing the incoming signal to see if it's accurate. The capture card is usually the culprit for color/IRE/brightness/etc issues, not the analog hardware (VCR, TBC).

[Angies_Husband]

Quote:

Originally Posted by lordsmurf

I'm not fond of generated calibration bars because those may not actually be calibrated, especially mid-workflow gear. You need to calibrate from the 1st device through the last, not just the middle. Some give no means to adjust calibration anyway, so it becomes moot.

That is a good point. So perhaps another topic, but is VCR calibration something that needs to be fine tuned, or is it something where it is either "correct" or "very wrong" and not a lot in-between? I guess I am talking about the techniques listed in service manuals that describe playing back an alignment tape to verify that the FM Waveform is flat (and otherwise making various adjustments to fix it)...
Is it safe to say that if you are playing back tapes and they are tracking correctly you don't have an issue?

Quote:

Originally Posted by lordsmurf

I'm not a fan of that TBC ... but with TBCs getting more scarce, I guess it's not always easy to choose an ideal unit. Essentially I'd trust color bar generated by it even less than normal.

Ok, so something to also check. Is this one of those cases where if you feed that bars directly to a waveform monitor and vectorscope, and they check out ok, then you can trust it?

Yeah, regarding the TBC model, I tried extensively to track down ANY of your recommended models... They are essentially extinct from what it seems. On the flip side, it seems that eBay has a generous supply of broadcast SD gear that is being cycled out at salvage values. Could be an opportunity to educate folks on why particular models are better than others. There is a large knowledge gap in terms of what to even look for, and newbies are left with either a "No TBC workflow" or playing roulette and hoping they get a good pro unit and and figure it out on their own.

I do laugh to myself that my biggest complaint so far has been: 1) it is a full 1RU pizza box (19" deep!), and is somewhat awkward to put anywhere, and 2) It sounds like a 747 taking off, so you need to sink more money into it to replace the fans! LOL

On the plus side, I am simply amazed of the impact of BOTH the VCR level TBC, and the External TBC... It is really night and day difference. The points you have made in previous posts still hold totally true.

Quote:

Originally Posted by dpalomaki

With everything calibrated downstream, you can use commercial recordings to "eyeball" the quality of VCR's output for problems. Commercial tape playback should remain legal on the waveform and vector displays. Bright whites should hit around 100 IRE, and blacks around 7.5 IRE (for USA NTSC).

@dpalomaki - so you are saying that if you take commercial content, you can use a presumption that certain scenes should for a max white, or min black level? So for example, a predominately snow scene from the planet Hoth in Empire Strikes Back should be maxing out at 100 IRE?

[lordsmurf]

VCRs need scopes, and internal adjustments if wrong. Something like Panasonic caps issues can make a real mess of values. But in general, it's either correct or really wrong.

Tracking is a completely separate issue, and that can use realignment from time to time. Special tapes not needed.

With TBCs, patience is required. Anybody wanting a TBC should PM me, and I'll try to keep them in mind when one becomes available next. eBay isn't the only (or best) source for locating them, and I have contacts.

I have rackmount TBCs due to noise, size, and sharp edges -- not just due to (usually/mostly) NOT being made for VHS sources. There are some model units that can be customized, and I've done that quite a bit. You have to disassemble the unit (sometimes easy, sometimes not), often cut wires for fans, and sometimes block/disable non-TBC aspects. Fans often add image noise, not just sound noise. Many need disassembly merely for a quality cleaning, because these ran 24/7/365 when in use.

On the IRE, not necessarily. You need a plurality of sources, don't trust anything to ever be correct.

[dpalomaki]

Quote:

...so you are saying that if you take commercial content, you can use a presumption that certain scenes should for a max white, or min black level? So for example, a predominately snow scene from the planet Hoth in Empire Strikes Back should be maxing out at 100 IRE?

Read more: http://www.digitalfaq.com/forum/vide...#ixzz5eDLobDLV

Not exactly. First VHS is kind of sloppy, so what you get may not be consistent. However, commercial tapes should, over all, be more accurate (and within gamut) as a whole. But some might not be according to standard. Home made tapes, copies, and cut-rate tapes are more likely to be off. Bottom line, comparing to several good commercial tapes can be better than nothing.

Second, in an average scene with a full range of both deep shadows and bright highlights, not dominated by either extreme, you can expect the deepest blacks to be near 7.5 (for NTSC) and highlights to be near 100 IRE. But this is not assured for any given tape.

For an accurate reading when measuring a signal it should be terminated with the correct impedance.