View Full Version : Live Feed Sync slow

08-04-2004, 04:49 PM
I work for a church and we are using VT3 for our service production needs. We have a supermicro Server with dual processors, 1 gig ram, 120gb system drive and 170 gb SCSI array set at Raid 0. We are using windows XP professional, and also have a RS-8 and a SX8. Should there be any delay? One member of our staff went to NAB and said that they could not see any delay on the VT3 system that was on display. What do I need to do to get the same results?

Please help.........

08-04-2004, 09:14 PM
Could you elaborate a bit more on what type of delay?

In projection/audio sync, switching of cameras etc.

Thanks ,


08-05-2004, 07:08 AM
It is a audio to video delay that is seen on our projectors.
We are using Barco projectors, which I thought were some of the best. But the delay is very visable. Will a bigger scsi array help?? We have 170gb now.

08-05-2004, 10:10 AM
Larger SCSI drives will NOT help. Any digital Switching device will have a 1-2 frame delay.
The real delay comes from the projection of the signal. This is true with any projection system I know of.
One option, if the delay is unacceptable is to get an audio delay device. Then you can set the audio delay to match. You will probably be looking at about a 4-5 frame delay going through everything.

Here are some links I found by typing in "Audio Delay" on my browser.

08-05-2004, 04:02 PM
That you for the information. But the delay seems to be more than 1 to 2 frames. The delay is very visable to everyone in the room. Right now I have my 2 Braco projectors (which from what I have been told are "top of the line") coming directly our of 2 of the video component outputs of the BOB, and am using the other 2 outputs for CCTV and VCR. Sould I get a nice video distrubiton amp (like an Extron) and only use one output from the BOB and have the rest come off the AMP? Would that help take some of the work off the BOB?

08-05-2004, 04:19 PM
It's not absolutely clear to me from the posts above -- is your problem that there is an obvious (but in sync) A/V delay, or is your audio out of sync with the video at the projectors.

If by chance the latter, are you running your audio through the SX-8/VT combination and out to the projectors - or straight to them?

08-05-2004, 04:57 PM
and... if the latter




might help

chock full o info

08-05-2004, 07:01 PM
Thanks for filling in the blanks, Jim :)

08-05-2004, 07:20 PM
The problem is that we are having sync problems with the video coming from the VT3 and the sound coming from our sound board. The VT3 is not suppling any audio (except for when we run videos). I am not experienced at all with Genlock. Are you saying that all I have to do is connect the Genlock connections directly from one cammera to another and they will be synced? Or do I then have to connect them to the BOB on the Genlock connection. Or will that only work if I purchase the Genlock card.

08-06-2004, 06:11 AM
To begin with, by running the video through the VT, but not the audio, you are causing a discrepancy (A/V sync error) right off the bat. Apart from that, there is an unavoidable latency of a few frames going through the VT, and very likely an even higher latency going through the projector. I gather that use of the genlock may help a bit with the VT's latency, but there is a point beeyond which it is irreducible.

The remaining combined latency may or may not be objectionable, depending on screen positioning and a lot of other factors. You should easily be able to find some discussions of these elements including some tips on how to optimize the physical layout with a search in this forum -- it's often come up before.

08-06-2004, 07:44 AM
How would I be able to run both the audio and video from the toaster. We are using a 64 channel K2 sound board and we have a matrax coming to feed the toaster for recording purposes, and we send on one channel to the board for movies. As it is we have to have all other mic muted when we play videos from the toaster or we get a terrible looping. Now you are saying that all the audio has to come somehow from the toaster to the sound board. How??

08-06-2004, 08:52 PM
Ok so it looks like Genlocking is the key to help this problem. So my question is how..... My cameras all have BNC connectors for genlock. How can I use the VT3 to genlock these cameras. Do I connect the cameras and the VT3 in a loop with the Genlock IN and Loop connectons on the SX8? If there someing else?

Keith Gandy
08-07-2004, 12:43 AM
Here is another voice. We are using the same setup for our church system, although we are only using a 32 channel audio mixer (Heath and Allen) that has four monitor outputs.

There is a latency in the projection, Genlock won't eliminate the problem entirely. The combination of the Toaster and projector latency equal .27 seconds in our tests (without GenLock) - but then again we are in a PAL (25 fps) environment. A combined six frame delay on a 25fps signal would roughly be a quarter of a second delay. Our tests were also made from a distance of roughly 35 feet from the stage (audio travels slower than light).

The audio signal that the SX8 receives is from a monitor output, not the main output. Each channel can be set on the monitor output - the VT is closed. This prevents loopback since the Video Toaster audio is eliminated on the monitor output.

When recording hard copies (ie VHS or DVD), we take the main output and delay it with a stereo hardware solution (relatively inexpensive) so that it matches the delayed video.

The audience has never complained about the delay although it is visible to the naked eye. It is most noticible for instrumentalists. We've adjusted to the difference.

Hope that helps.

Dan Hong
08-09-2004, 10:25 AM
One more variable to this equation. How are you getting the signal from the VT3 to the projector. In most Church environments, we've seen the projector recieving the signal via VGA or RGB inputs and not a video signal (component composite or y/c). This means that somewhere in the system is a video scaler (or RGB switcher). Depending on which unit you have, there can be as much as 10 frames of delay in the scaler (not so noticable when you're feeding a Powerpoint of the sermon notes, but almost comical when you're feeding a live camera). So the VT3 gives you 1-2 frames of delay, the projector may be giving 1-4 frames of delay and a scaler may add another 2-10 frames. If you're feeding a video signal into the Barcos, check the specs on the projectors. If they are meant for a computer native format, then they probably are scaling the video up internally, which is another delay.