Horizontal/Vertical Synch + composite for monitors

[timcheng00]

i was just looking though my ATI control panel and came across the Advanced tab under the Displays window.

there are options to select either or both of Horizontal and Vertical Synchronization [ (+) is off, (-) is on i think] and an option to check "Composite."

i tried selecting all of them and my monitor (Samsung SyncMaster 910v) still works properly. but i'm curious as to what each of these things mean. anybody care to explain?

 

[JimPhelpsMI]

Hi Tim, Composite Video carries Video, sync and sound mixed on one conductor with a shield. RCA on both ends and coaxial cable for the conductor. Standard audio cable works OK. It would be used to run a TV. The Horizontal and Vertical would only be active on the composite output and would stop vertical roll and horizontal slideing of the picture. I assume that if you checked the back of your computer you would find an RCA output jack near the Normal monitor connector. You would probably need a composite to antenna (RF) converter to use it unless the TV has a composite input. Jim

 

[VirtualLarry]

Yeah, but composite video is not the same as composite sync. Composite sync simply means that both the H and V syncs are carried along the same signal. Sync-on-green takes that one step further, and puts the composite (usually) sync signal on the same wire as the green (RGB) video signal. They can be filtered out because the sync is usually TTL, and the video signal is analog 0.7v P-to-P.

Normal "VGA"-type PC monitors use seperate H and V sync signals, along with seperate R,G,B analog video signals. Don't worry about "sync polarity" either. In ancient days, with multiple-fixed-freq CRTs (before the days of true "MultiSync", which NEC trademarked (?) and basically also pioneered), video cards would tell the monitor which fixed sync circuitry to select by the polarity of the H and V sync signals. Nowadays, with DPMS-compliant monitors, the CRTs will auto-sync to the frequencies, and instead use the polarity of the syncs to select a power-management mode/state.

Generally, unless you have an ancient CRT or one with "special needs" (like some of the sync-on-green workstation monitors that I have), then you don't need to worry about messing with those settings at all. Just select "Plug and Play Monitor" (if it supports DDC/DDC2), and be happy. 🙂

ATI cards that have a TV-out feature, will also have a port that contains both S-Video and Composite Video signals, which can be controlled from a seperate panel in the ATI Control Panel settings, but that has nothing to do with the composite sync options under the CRT's advanced property panels.