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LZX Sync Generator problems?
MUFF WIGGLER Forum Index -> Video Synthesis  
Author LZX Sync Generator problems?
fletch
I just received my first LZX modules: sync generator, ramps and CVE. Connected everything up, bars and ramps work fine, but when running an external video signal in, it doesn't seem to sync to it and I get picture that scrolls horizontally (moves left and right) off the screen when in EXT sync mode. When in internal sync mode, it jitters back and forth. I'm not sure if I'm doing something wrong or if the sync generator is defective.

(BTW the same source (VCR) works fine through the Jones MVIP).
lizlarsen
Hey Fletch!

VHS tape sources won't play well with the LZX as a master sync source/ext lock input, the timing is not stable enough since it is being played back off of tape, and the LZX sync generator is expecting a stable master timing source in order to lock to it accurately. That's the jittering you're seeing. If you want to use a VHS tape as a source, you'll need to run it through a time base corrector, or a video mixer with an integrated timebase corrector first.

Do you have a DVD player or a video camera handy? Try running those in, and tell me what you see -- just so that we can make sure your units are functioning correctly.
fletch
cool, DVD source worked fine. thanks Lars
Matos
Would the mvip also time correct he signal? As in source into mvip into lzx?
johnnywoods
i also think the VCR in question might have something to do with it. I run my VHS into the LZX all the time, with no problems seriously, i just don't get it
lizlarsen
Matos - it might, but I'm not sure enough how it works and what chips are used.
Johnny, you probably have a VCR that has an integrated TBC or some stabilization circuitry. I had one like that, and it worked great for sync'ing.
daverj
Matos wrote:
Would the mvip also time correct he signal? As in source into mvip into lzx?


No. The sync out of the MVIP is locked directly to whatever you feed in. There is a slight delay horizontally, so the sync out is slightly out of phase with what goes in, but derives it's sync from the input.

So garbage in, garbage out.

The MVIP just has a fairly accurate sync locking system that has built in adjustments to detect and lock to unstable video sources (within reason). My upcoming genlock module also has that ability, as does the TBC that will be coming in the spring.

While many genlocks will lock to VHS, there is a reason it should be avoided. When you lock to an unstable sync source, your whole video system is running with unstable sync. That means that whatever new images you create will have old, unstable sync when you go to record them. Plus even if the genlock of the system locks to it, any genlock cameras that are part of the system might have trouble with it, or might lag behind in their locking, causing the camera output to not just have the unstable sync of the tape, but to have even worse sync.

Every time you copy a VHS tape the sync gets worse, so the more generations of tape (the more times it was copied) before you try to lock to it, the worse the sync is when you genlock to it. Also as a tape player ages, the belts and other mechanical parts wear down, so even 1st and 2nd generation tapes might not be so stable.

A high end player with timebase correction helps. Another method is to transfer the tapes to a computer and burn DVDs. That timebase corrects them. Or instead of using DVD you could use a solid state or disk based player, like the WDTV or Popcorn Hour. Even though they are primarily HD players, they also have standard SD outputs. Genlocking to those should always work, and the sync will be pretty stable.
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