User`s manual

Alcorn McBride Digital Video Machine HD User’s Manual Rev 1.0

Synchronizing Multiple DVMHD’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 DVMHD’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 DVMHD’s, two

requirements must be fulfilled. First, all DVMHD’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 DVMHD’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 DVMHD’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. If the Play command is

issued too close to the end of a frame, this 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 many

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 DVMHD’s.

Sharing Video Sync Between DVMHD’s

The first step in sharing video sync between DVMHD’s is to obtain a Video Sync

generator. Although Alcorn McBride does not manufacture this product, they are

commonly available from many different manufacturers. Once you have a generator,

sharing video sync is just a matter of wiring the sync generator to the DVMHD’s.

Here’s how it’s done:

1. First, verify that each DVMHD is configured to receive the type of sync

outputted from the sync generator. Blackburst is the most common, but C-

Sync is also supported.

2. Verify that the 75Ω sync termination of each DVMHD is enabled.

3. Using standard BNC cables connect the sync input of each DVMHD to a

dedicated output on the sync generator. Verify that the yellow sync LED of

each DVMHD illuminates when the connection is made.

If you’ve successfully completed these steps, you’re ready to move on to the next

section about triggering these DVMHD’s to play in sync.