This page gives a general description of “sync” and how it relates to game consoles in an RGBs signal.
Sync literally means the synchronization of lines on the screen. All analog video signals carry some type of sync signal; Composite video carries all of the video information (all of the colors and brightness combined), as well as the sync information to your TV. S-Video is similar to composite, but separates the signal into two parts: Chroma (color information) and Luma (brightness information and sync).
RGB signals separate each color into their own channel (Red, Green and Blue) and carry both the horizontal and vertical sync information in it’s own separate channel called “composite sync” (totaling 4 channels). This is called “RGBs”.
It’s common to stumble across articles or forums posts where people use different names to describe sync (“regular sync”, “pure sync” “raw sync” , etc). This was extremely confusing to me when I first started learning about sync in game consoles and I want to make sure this page clarifies that! In the context of game consoles, there’s really only four types of sync any beginner or intermediate retro-gamer needs to know:
csync – This is just the composite sync info with nothing else on the line.
composite video as sync – This uses the composite video line as sync.
sync on luma – This is using S-Video’s luma pin as sync
ttl sync – This is essentially the same as csync, but voltages are over five times higher!!! Almost all standard equipment used requires csync and ttl can actually damage SCART equipment!
In most cases, it’s best to use csync, as there’s no other information in the signal which could cause possible interference, or incompatibilities with your setup. Certain consoles (PAL SNES & N64) don’t have csync as an option and in this case, it’s best to use luma, since it contains the sync signal, but not as much information as composite video. You can also use composite video as sync, but interference could occur, since there’s so much information traveling through that line; The most common result of that is colors “bleeding” between pixels on the screen, causing the picture to lose sharpness (and on some displays, it may cause interference nicknamed jailbars). In either case, if your setup requires csync, but you only have luma or composite video to work with, you can still accomplish that with the help of a small circuit called a Sync Stripper:
Some switches, displays and upscalers require composite sync (csync) and won’t work if you try to feed it composite video or luma. In these situations, you could route those signals through a circuit that filters all other information from the signal, except sync. There’s a few devices on the market available that will do this for you, called “sync strippers”. A common plug-and-play solution used with video game consoles is the Sync Strike. You can also purchase pre-made circuits, or make your own, using a chip called the LM1881 (see links to the right). I’ve created a detailed guide if anyone would like to try and build their own sync stripper:
There’s also a page for more advanced users that shows how to get csync from each console:
As an FYI, you may come across terms similar to RGBs, such as “RGBHV” and “RGsB”. Just to clarify, here is a basic description of each:
– RGBs is simply Red, Green, Blue and sync. In RGBs, both the horizontal and vertical sync signals are combined into this one line.
– RGBHV is essentially the same as VGA. The “HV” means there are two cables for sync, one for horizontal and one for vertical, totaling 5 channels.
– RGsB is “Sync on green”: Literally, the green cable also carries the horizontal and vertical sync signals, totaling only three cables. Most displays are not compatible with RGsB, so you’d need to pass it through a device that will separate the sync signals into a more common signal, such as an Extron RXi.
Hopefully this page covered all the basics you’d need to know about sync. I purposely over-simplified a few of the details in hopes that it would make this page easier to understand, but I’ll someday have a video with more detailed information about what sync does and how it interacts with different gaming equipment.