TBC generated test patterns and scopes usefulness?

[ELinder]

OK, this is probably a noob question, but I've been learning about capture scopes and their usefullness looking thru the forum here and reading a number of refernced articles. What good is a TBC generated color bar pattern if the image controls don't change the signal output? I'm testing ScopeBox, a Mac scope and capture program. My TBC-4000 generates a color bar pattern of 8 bars at 100%. From the scopes, the luma and chroma are a little bit off, although not much. I thought the way to correct this was to use the TBC image controls to bring it back to where it should be, but the controls apparently do not change the pattern, only whatever video signal is going thru the TBC. So what is its usefullness then? Do I need to record that pattern onto the VHS deck to check the whole pipeline? Of course that will tell me how good the VCR/TBC combo is, but is worthless for any other tapes I play.

Also from the articles I read, it seems if the black levels are too low they can cause noise by interfering with a synch signal. So how low is too low? I've seen some captures where the black level is well below 0 instead of the recommended 7.5. In that case is it recommended to raise it before capture to avoid that noise?

Any pointers on where to further learn about NTSC/VHS signals, test patterns, and input scopes would be appreciated.

Erich

[dpalomaki]

The color bars, if they are accurate, can be useful it you want to test/adjust the full analog signal path to ensure each step in the chain (including capture) is performing properly. This can be useful to help ensure you accurately capture what ever comes off the tapes. You probably will need a vector scope capability to make full use of them. (You can also use them to assess aspects of record/playback performance of a VCR and perhaps adjust the VCR electronics if you have sufficient technician skills and equipment.)

The standard SMPTE bars with the bottom 1/3 of the displaying "PLUGE" also can also be used to adjust monitors/TVs, especially monitors with a "blue gun only" capability.

A typical use would have been to record bars(and tone) at the start of a tape to allow level and color adjustments at later playback. However that was not common in home/consumer recording practice and would only be valid for the that recording. They may not be useful for material added to the tape at a different time or or by a system.

Some consumer/prosumer gear added "bars" capability as a marketing gimmick but they may not have been very accurate.

[jwillis84]

dpalomaki is spot on.

I was/am a newbie and hauled a huge glass crt waveform monitor and vectorscope from a university video lab and hooked it up to learn about all this.. my take is it was useful mostly from a confidence perspective. That is confidence I could see and understand color bars and how they got decoded on the screens.

Realtime when actual video is playing through them it gives you a "sense" of what is going on but nothing super useful.

The waveform monitor can basically help you adjust your brightness and contrast levels, the absolute blacks and whites, or [range] so that it fits within that expected by your capture device. If the brightness and contrast values fall outside this range the capture won't be as good as it could be. - but this is usually outside most peoples understanding, or most people don't want to fuss with it for each and every tape.

The vector scope adjusts "saturation" and "hue" which are really advanced topics, often better left alone. Sat is the absolute range of the color values, akin to the brightness and contrast. Hue is the relative "tilt" of the colors to what they should be from an original broadcast source, sometimes its gets skewed in a transmission or cable and this fixes that.. but its not really for color correction... it skews "all of the colors" at the same time, not just one.

The controls for these are laid out on a proc amp by order of relative importance, brightness, contrast, saturation, hue.

If you only had one control brightness would be the most important, and so on for each of the others. And the one you most don't want to mess with is the far right or "hue".

In general these were for fixing a signal to "broadcast standards" by fcc rules and weren't meant for consumers.. tweaking to "measure up" to broadcast standards and making professional DVD standard captures just wasn't their intended purpose.. and I think I hand wringed a bit too much over these controls.. time would be better spent on getting a good VCR with tbc and denoiser circuit, and an external tbc and a good capture card that gives you the choice of virtualdub or mpeg2 capture. Bonus with a good tbc is most true or false copy protection will be neutralized, so there is extra incentive to find an external tbc.. but they are becoming hard to find.

If you get a proc-amp, the SignVideo / Studio 1 proc-amps have a bargraph LED meter for adjusting Brightness and Contrast values, but nothing for the Sat, Hue controls.. which is pretty much optimum.. too much control can get you in trouble fast. And its probably just as valid for detailers, like the DR-1000.. in the hands of a professional it can make a great difference.. but in the hands of an amateur, not a lot of difference.

I think its been wisely said before, that tweaking by your own eye and experience is usually good enough.. and if you have real doubts, don't throw out the tapes after capture, and/or capture in lossless with virtualdub so you can fix things later.. lossless is expensive, but you'll know if its worth the cost.

Fixing mpeg2 captures.. just don't rely on that possibility... and mpeg2 was optimum for interlaced video, mpeg4/xvid/divx much less so.

[ELinder]

The ScopeBox software scopes are pretty cool and can be used on any live input or an already saved video file. Heck, at $99 it's a no-brainer compared to what I understand hardware scopes used to cost. The saved peak features definitely help see a trend in the capture for adjustments that should be made before capture.

As for the TBC generated bars, I'm still not understanding their usefulness other than if I were to record them to a tape and then use that tape to record something else on the same deck and tape.

If the proc-amp adjustments on the TBC don't adjust the color bars output, they're basically useless for tuning the TBC's color bar calibrated output, correct? Obviously the controls are useful for adjusting the video signal that's coming the the unit from the VCR, then I can use the scopes to adjust before I capture.

Erich

Hm, the upload is squashing my image. It was 1580x890 and 595 KB

[jwillis84]

Hardware scopes are terribly inexpensive these days, often free just for hauling them away.. they're crt's in 2018 egads!

But Osprey cards are going for $10 or $20 on some auction sites and their driver software has builtin "soft scopes". Osprey has been in business like 30 years and play to the raw capture crowd for streaming, usually 8 bit capture.. so there are better options for VHS.. but their drivers are very stable.

The big difference with Osprey is their premium Simulstream option, which lets you break up one capture stream into many in the drivers to feed multiple encoder engines simultaneously, those cards look the same as the basic cards, but cost hundreds more... not a feature the VHS crowd would be interested in.

In fact I'd say avoid Osprey except for the fact they are so cheap, more something to play around with.

[dpalomaki]

Quote:

I'm still not understanding their usefulness other than if I were to record them to a tape and then use that tape to record something else on the same deck and tape...

That may be the extent of their value to you. For most consumers the bars serve no purpose beyond eye candy of a sort. But for someone who is maintaining an analog video signal system; i.e., passing the video through multiple devices such as amplifiers, mixers, frame synchronizers, repeaters, as well as recorder/playback devices and digitizers or transcoders, and displays the bars provide a standard, known signal that can be used to identify problem devices and/or align/calibrate devices. With the right test equipment they should be much more precise than eyeball. Important for broadcasters and producers of content for distribution, and content distributors.

If the user could change the bars some arbitrary amount at will by, say using the proc amp, they would no longer be a "standard" and thus not fully useful for system testing and adjustment. One would typically use the proc amp to correct errors in the VCR playback of prerecorded bars, but one normally would NOT want a proc amp to alter the bars when they are being recorded.

Assuming a spot-on video input, one wants the output of the chain, and each step along the chain, to match. If not one could trash the signal by introduce artifacts such as clipping, crushed blacks, additional noise, gamma shifts, and color errors, along the way.

[ELinder]

OK, thanks all, I think I understand now. I was thinking in terms of adjusting instead of thinking in terms of checking to see if it's still in spec.

Erich