Composite Sync vs. Sync-on-composite signal quality question

Recently I found this a video that talks about different kinds of sync in video signals. They discuss composite sync vs. sync-on-composite, and they conclude that composite sync by itself gives a better quality signal than sync with the composite video.

The section of interest starts at 9:20:

https://www.youtube.com/watch?v=LAlrdCBjUAQ

In this section they show a video capture from their XRGB Mini, which exhibits a checkerboard pattern on solid colors when using composite video as sync, but no such artifacts when using composite sync.

I have seen this discussed in a few other threads, with some stating the same, although there seem to be many people who have never noticed a difference. A few have stated that using sync stripped from the luma line gives just as clean results as composite sync.

So my question is, from your experience, is this true? If so, why? And why would drawing the sync from luma be better, since it also has video on the same line?

I also found this article that talks about analogue video signals:

http://www.maximintegrated.com/en/app-notes/index.mvp/id/1184

In the "Scanning and Sync" section, they state:

"The sync portion doesn't interfere with the active video because it's below the black level and can't be seen. Any signal below the black level is said to be blanked."

If this is true, how is it possible that the composite video signal could interfere with the sync? Or could it just have to do with the way the display handles sync, i.e., the XRGB Mini?

 

I can't explain why besides there being video mixed in there and perhaps the sync signal is weaker when mixed but I have noticed that there is definitely image quality difference when using C-Sync and Composite video for sync. I tested this with the NESRGB board with a custom RGB to Component board and using Composite always had off colors and the checkerboard effect, but with C-Sync the image was clear and the colors were correct and no checkerboard effect.

 

That statement is referring to composite video. In composite video, the sync and the video signal are one. I'm not sure if the problem is from using composite video for sync but if it's because of the fact that the sync signal is weaker in the composite video signal compared to a buffered composite sync. I think it's a case by case basis though. Some monitors might work fine with composite video, some might not. And it is most likely how it handles the sync signal input that differs.

 

A CVBS signal contains a superset of the information that's in the composite sync. The reason that it doesn't work well in some cases is simply that you are feeding it into a device that was designed to accept composite sync only, and doesn't have the proper processing for handling a video signal. Some Sony PVMs are like this (because TV studios normally use a clean sync feed) and so is the XRGB (because it was designed for use with devices supporting the 21-pin Japanese AV port standard, and that has a dedicated sync pin).

It's not really a question of one being "better" than the other - it's just a matter of what a specific device is designed to handle.

 

Thanks everyone for the helpful replies. Does this mean that I would get the same quality on my XRGB Mini with a composite sync cable as I would with a composite video cable with a sync stripper?

Does this mean I might also have to boost the sync signal from the composite video line?

 

i would try out a sync stripper if you can't use composite sync. It should work.

 

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