|Posted on February 28, 2010 at 1:01 AM|
tri-level bi-levle sync SD and HD are 2 different standards. They require two different types of sync.
SD bi-sync and HD tri-sync are different signals.
SD Bi-sync supports computer video, composite video, s-video, andcomponent video, by using 2 voltage levels ( high and low )... systemsusing bi-syn are triggered by the differential voltage at the leading (negative) edge of the signal. Bi-sync basically runs at 0 votage (black) then drops to a negative voltage and then back to zero ( 2states or BI-sync)
Tri-sync provides a more exacting sync for the 3 component signals. HDhas sync info on all three channels ( Y, Pb, and Pr). Tri sync startsat 0 volts ( video black ) then goes negitive, then a positive voltage,then back to 0 volts ( 3 states, Tri-Sync). This also fixed theintroduction of a voltage differential by bi-sync signals into theactual video signal. the tri-sync signal is triggered by the on thenegative transition, then on the positive transition. thus0,-300mv,+300mv,0 3 sync points... This all happens in the Horizontalblanking interval. There is something called the White reference levelthat is set at 700mv. the 700mv drops to 0 at the start of the blankingperiod. the signal drops to -300mv, the to +300mv, then to 0 the backto reference white 700mv. This is the HD Analog horizontal timing datawhere HD tri-level sync is used. ( I don't remember what the whitelevel is for bi-sync.. sorry pulling most of this out of my head... )There are also a couple of issues revolving around the Progressive vsinterlaced HD frame timing that comes into play here.
bi-sync is on the Y-signal on SD video. tri-sync is on all 3 channels for HD. ( check out SMPTE 274M ad SMPTE 296M )
so the two are incompatable for sync .. there are a lot of options out there for devices that support both bi-sync and tri-sync.
the sync IO accepts SD BiSync or "traditional" video black, the HDSyncIO accepts Tri-sync signals. As far as gear it all depends on what youare syncing... if its protools to an HD video deck and you are layingback audio, you can use a tri-sync box that offers bi-sync. The bisynccan be routed to the protools rig and the tri-sync can be used for theHD deck. If you are dealing with laying back an HD video signal from avideo editing system with an AJA Kona3 card to an HD video deckdirectly connected, you don't need
a tri-sync gen, because the AJA kone3 offers this to the deck via thevideo signal (read the Kona3 card for details, i don't remember exactlyhow they do it, but they do) if you are using a euphonix system 5 HDMIIO and a HD video deck you need a tri-sync generator. So it all dependson what you are trying to sync.
I hope this helps a bit with some of the tech background.
ms georgia hilton mpse cas