Reply To: Audio but no Picture.

NewHome Forums OSSC & OSSC Pro OSSC – Discussion and support Audio but no Picture. Reply To: Audio but no Picture.

#24818
nmalinoski
Participant

So sync-on-luma is basically identical to CSYNC (both sH and sV are shoved into a separate/unused cable). And for anyone who doesn’t plan on making its own cables and has devices that accept every type of sync, CSYNC is basically identical in terms of quality as Sync-on-luma.

When it comes to providing sync for RGBS applications, composite video, luma, and clean composite sync all serve the same purpose. In poorly-shielded cables, composite video tends to cause a lot of interference, because it also carries video data (in the form of luma and chroma signals muxed together).

Luma, lacking the chroma/color data, tends to cause far less interference to RGB signals (generally imperceptible), and is preferred over composite video for RGBS on consoles that don’t provide CSync, like the PS1 and PS2.

Clean composite sync has no video data to cause interference, so it’s considered the best option, and is actually required by some (most?) pro AV equipment, like Extron RGB interfaces; however, most consoles don’t provide clean composite sync output (not without a hardware modification, anyway), which is why you’ll see people recommending sync-on-luma cables. CSync cables for consoles that don’t natively output CSync will have a sync stripper built in somewhere (connector casing, inline box) and are really only needed for interfacing with pro AV equipment.

Which means that RGB cables don’t have luma running in a separate cable but along with red, green and blue I guess… (I always assumed luma was on a separate cable… if S-video and YPbPr can do it…)

It depends on the cable and how it’s wired. When it comes to SCART cables, you have 4 lines, R, G, B, and sync; and whether you use composite video, luma, or clean CSync on that sync line is up to you (at least when you’re ordering boutique cables from places like Retro-Access or RGC).

Which makes me think : Is there a cable that divides R,G,S, luma and sync ? From my point of view, the best of the best would be RGBHV because everything is separated, I always assumed RGBHV was actually RGBHVL (“L” would stand for luma). Is such cable exist ? Wouldn’t it be the ultimate cable (especially if fully shielded) ?

There’s no point in running luma and sync separately, because composite sync is always muxed into luma, so it can function as a sync signal; generally you’d run one or the other depending on the capabilities and requirements of the equipment you’re connecting.

Granted, I’m not the brightest, but this thing is not often explained very well. I’m going to re-watch MyLifeInGaming video about sync to see if I had a chance to understand. (if they did explain that right, I’m going to feel stupid)

It’s not the easiest topic to follow, due to reuse of the same words for multiple, discrete ideas. I know one of those MLiG videos touches on the differences of and confusion caused by the terms composite sync and sync-on-composite; and it’s not often clear that voltage plays a part in all of this as well. It would be really nice if a lot of information on Bob’s site was explained as if we were 5 years old before getting into the eye-glazing technical stuff. 🙂