Reply To: Audio but no Picture.

#24814
nmalinoski
Participant

@BlueStinger

Correct me if I’m wrong but sync-on-green means sync-on-luma and both mean RGsB, YPbPr is sync-on-green and the green cable only carries Luma.

Sync-on-green, sync-on-luma, YPbPr component are all different ideas:

First, sync-on-green, also referred to as RGsB or SoG, specifically refers to RGB (hence the ‘RGB’ in ‘RGsB’) where composite sync is muxed into the green video data instead of being sent on a separate wire (hence the little ‘s’ in ‘RGsB’).

Secondly, YPbPr is a different transmission method altogether. Despite also transmitting sync on a green wire, no green video data is transmitted, so sync-on-green labeling wouldn’t make sense. If anything, YPbPr would technically be a sync-on-luma application; however:

Lastly, sync-on-luma, as understood by the community, refers to a non-standard wiring of RGBS cables for S-Video-capable consoles where luma is put on the sync line instead of composite video in order to significantly reduce the amount of interference caused to the R, G, and B video lines.

Same goes for Scart. A scart sync-on-luma (= sync-on-green = RGsB) is a scart where :
1 pin carries Red
1 pin carries Green
1 pin carries Blue
1 pin carries the sync signal on a separate line that is Luma (which would be used for luma if the scart were to be wired for S-video)
and the composite line would be unused

CSYNC (sync-on-composite) on a scart would be :
1 pin carries Red
1 pin carries Green
1 pin carries Blue
1 pin carries the sync signal on a separate line that is Composite (which would be used for a composite signal if the scart were to be used as a non-RGB scart)

Two things. First, “CSync” is short for “composite sync” and is most often used to refer to clean composite sync. Sync-on-composite instead refers to using composite video for sync.

Secondly, regarding SCART, there is only one sync line going into the display, pin 20. (There is some bidirectional stuff for composite video, S-Video, and stereo analogue audio, but that’s beyond our scope here.) Pin 20 is intended to carry whichever video signal has composite sync:
* For composite-only applications, this will simply be composite video;
* For S-Video applications, this will be luma;
* For RGBS applications, it’s typically composite video (sync-on-composite), but the cable could instead be wired to use luma (sync-on-luma; again, for interference reduction) or clean composite sync as provided by the console (very rare) or a sync stripper (common in boutique/custom cables); and
* For YPbPr and RGsB applications, pin 20 will have no signal, as sync will instead be put on pin 11 (These formats are, for the most part, not supported over SCART).

Y from YPbPr = green cable = only luma (no color) = sync, but that’s a “happy accident”.
What we call it “green” in that case is supposed to refer to the color coding of the wires but not the video signal, or did I get this wrong ?

You could very well argue that “sync-on-green” refers to the cable color or wire designation, but to me, it makes more sense that “sync-on-green” refers to sync being muxed with the green color data. The coloring of cables is trivial; if cables for luma were any other color than green, would we even be having this discussion?

Because if I’m wrong (and I could be), this means that RGsB (sync-on-green) is not equal to sync-on-luma. In that case, are we supposed to use the term “sync-on-green” only when referring to YPbPr ? And sync-on-luma only when referring to scart or s-video ? Does that mean that the green color (video not color of the cable) carries the luma ?!

To recap: No, sync-on-green is only RGsB; no, sync-on-luma refers to any RGBS application where sync is provided with luma (cable/connector style doesn’t matter); and, no, green and luma are two separate things.

https://www.retrorgb.com/sync.html
In this page, Bob list the types of sync signals twice. Once sync-on-luma is part of the list, and missing from the other list. And in the second list he talks about sync-on-green and sync-on-luma is missing. So, he forgot a sync signal in both lists ? Or can I use them interchangeably ?

The lists on that page cover everything, but I would say it’s not the clearest of information.

There are three things to be considered when it comes to sync:
1. Which wire is transmitting the sync signals? (Composite video wire for composite video, Y for YC and YPbPr, G for RGsB, S for RGBS, and H and V for RGBHV.)
2. How is the sync being provided? (Composite sync bundled with video data for composite video, YC, YPbPr, RGsB, and [usually] RGBS; clean composite sync on its own for RGBS; or clean, separate horizontal and vertical sync signals for RGBHV.)
3. What is the voltage of the sync signals? (~5Vp-p for separate sync for RGBHV and clean composite sync when provided directly by a device like a SNES or Extron CrossPoint, which is fine for something like a VGA monitor, but can damage SCART and other consumer AV equipment; everything else is ~1Vp-p by virtue of sync being bundled with video data or being provided by a sync stripper that correctly attenuates the sync voltage for consumer equipment.)