Signals can be combined — but carefully.

Combining Sync and Camera Flow Diagrams

You can combine aspects of the two flow diagrams by eliminating a few parts and combining others to make it simpler. Follow the route of the reference signal. Following the reference signal in the figure at the right, you see that it goes from the sync generator to a DA. The first DA output goes directly to the production switcher. The second DA output goes to the camera 1 CCU. From the CCU, it goes to the camera head and is combined with the video information. That composite video leaves the camera head, returns to the CCU, and from there goes to the switcher. The third DA output follows a similar path: DA to CCU, to camera head, back to CCU, and to the switcher.

Although only one specific system has been discussed, all systems are basically alike, whether using 2 cameras or 20. There will be differences, but the basic technique of running the sync through DAs to the various cameras and taking the composite video from the cameras through DAs to their various destinations will be similar in any professional situation.

Out-of-Phase Cameras

If you study the figure for a moment, you'll see that each of the paths is a different length. Since electricity travels at a constant speed, it will take the sync signals different amounts of time to follow each of the paths. Thus, sync on each path will arrive at the switcher at different times and the cameras will be out of phase.What happens if you're on camera 1 and you want to fade it down while you're fading up camera 2 (this is called a dissolve)? Which color burst, for example, will the switcher lock up to? It can only use one at a time.

The switcher will lock up on the color burst from camera 1, but as the dissolve progresses, the colors on camera 2 will look funny since they're referenced to the color burst of camera 1 instead of their own. When the dissolve is completed and camera 2 is fully “up,” the switcher will lock to the color burst of camera 2 and the colors will snap back to normal. Fortunately, circuits in the cameras can be adjusted to compensate for the difference in distances traveled by the color bursts. However, if the cameras are not set properly and are out of phase, the problem described above will result.

Combining sync and camera flow.