User`s manual

Alcorn McBride Digital Video Machine DVM-7400 User’s Manual Rev 1.5
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Synchronizing Multiple DVM’s
The most common application of Digital Video Machines equipped with the External
Sync option is synchronizing multiple machines. When implemented properly, this
capability allows several DVM’s to maintain perfect frame synchronization with one
another. This is a critical requirement for applications that involve:
• Adjacent Displays intended to form a larger image (Video Wall)
• Edge-blended projectors (same concept)
• 3-D Theatres (require separate video sources for the left and right eye)
In order to accomplish perfect frame synchronization between DVM’s, two
requirements must be fulfilled. First, all DVM’s must be locked to the same video
sync source. This is the only way to guarantee that they will display each frame at
exactly the same moment. It is also the only way to keep the machines from ‘drifting’,
which results from them playing at slightly different speeds. The second requirement
is that all DVM’s must be told to play at exactly the right moment, and at exactly
the same time. To be more specific, this moment is just after a new video frame is
encountered. Telling the DVM’s to play at this precise moment ensures that they all
have time to process the ‘Play’ command and make preparations to begin playback
when the next video frame is encountered. Issuing the Play command too close to
the end of a frame will likely result in the players starting at slightly different times.
This is because some players might process the ‘Play’ command in time for the next
video frame, while others might still be processing the ‘Play’ command (forcing them
to wait until the next frame). The result of this is that each video has the potential to
be out of sync by +/-1 video frame. For the majority of synchronized applications, that
is an unacceptable margin of error.
The following sections contain information on how to meet these requirements and
achieve perfect frame synchronization between multiple DVM’s.
Sharing Video Sync Between DVM’s
The Digital Video Machine has been conveniently designed to daisy-chain with other
DVM’s so that they may share a common sync source without the need for a 3
rd
party
sync generator. Here’s how it’s done:
1. First, verify that each DVM is configured to receive C-Sync and that each
one also has the 75Ω termination enabled.
2. Pick a DVM to be a Master clock source. It really doesn’t matter which one
you pick, but it would probably be a good idea to pick one at the ‘beginning’
of your chain. (For example, if your DVM’s are stacked or rack-mounted
vertically, the top machine would be a good choice)
3. Using a standard BNC cable, connect the sync Output of the Master DVM to
the sync Input of the 2
nd
DVM in the chain. If both machines are powered
on, you should see the yellow LED on the back of the 2
nd
DVM illuminate
when you connect the cable.
4. If you have more than two machines, continue by connecting the Output of
the 2
nd
DVM to the Input 3
rd
DVM.
5. Continue this process until you reach the last DVM in the chain.
6. Check your work by verifying that the yellow LED is illuminated on every
machine except the Master.
If you’ve successfully completed these steps, you’re ready to move on to the next
section about triggering these DVM’s to play in sync.