Vectorscope, pattern generator to test VCR color accuracy?
 

Hello all,

I've recently started playing with a color bar pattern generator and a vector scope to see how different equipment affects the video signal in a capture chain.

To my surprise, on the few VCRs I've tested, I'm noticing that simply passing the known correct color bars over composite through a VCR very often changes the signal drastically on the output side. They also often seem to record/play back those color bars at far different levels as opposed to the original signal levels and targets. How far the lines connecting the color targets is a great "objective" way to visualize the degree of noise present as well.

So my question is whether anyone that has what they believe to be a well calibrated VCR is willing to post a photo of the vectorscope under each of the following conditions:

1. ColorBar Pattern Generator -> Vectorscope (while 75 ohm terminated) - this represents what the ideal playback "should" look like if the VCR is perfect at capture/playback. I don't think any of us actually expect it to be perfect, but I think we do expect it to be "pretty close."

2. ColorBar Pattern Generator -> VCR (while on and input selected that the ColorBars are going into) -> composite output to Vectorscope (75 ohm terminated). - This shows what the VCR does to the signal by passthrough alone. Ideally, it would be unchanged from #1

3. Same Setup as #2, but record the color bars for a bit on the blank tape, rewind, then play that recorded color bar section back and photograph what the vectorscope shows during that playback. Again, that would ideally look like #1 if it was a completely accurate capture/playback of the original source.

4. If your VCR has a TBC, turn it off during playback of #3 and take a picture of what that looks like on the vectorscope.


Unless my VCRs are just way off, I think you'll be surprised at the results. I'll post some of what I've gathered from my own here in a bit.