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Time Code Genlocking Title 

 

What are they and why are they needed? All video cameras have internal free running oscillating clocks that provide the timing for camera and video signals. Clocks differ slightly in speed due to tolerances, temperature variations, alignment, and component aging. When cameras are used in a studio configuration, each one must not only be locked together, but also timed so that when switched, there will be no horizontal, vertical, or color shift. Genlocking circuits perform that function.

Set-up for genlocking is very simple. You use a camera or video generator for the master locking source. Then either distribute this lock signal through a video distribution amplifier, or loop from camera to camera, taking the source cameras video output, feeding the second camera’s genlock input and so on. Using a waveform monitor and vectorscope you now adjust each camera’s H Lock (horizontal) and SC (subcarrier) controls to time each source. This method is used for switching live video shows or can be recorded as live on tape with a separate VTR.

For field production with reduced budgets the same shooting concepts are used, but the video is recorded onto individual camcorders and the tapes are either edited or switched later. In order to pull this off, each camcorder must record identical time code, which will allow perfect continuity between cameras.

Without going into a lot of details, in order to do this properly you must not only lock timecode but also genlock all of the cameras together. Many videographers think that only the time code must be locked but that method will result in video hits being recorded on tape due to that internal timing clock used in each slave camera. There is a timing relationship between timecode and the cameras internal timing signals. If not genlocked the slave cameras internal timing generator must adjust itself periodically to keep in time with the timecode-locking signal resulting in those hits on tape.

At least once a month I get calls from clients that have tapes recorded with these glitches that cannot be fixed in postproduction. There is no actual problem with their cameras, they just were not aware of this procedure. When genlocking and timecode locking, switch the slave cameras TC switch to free run and make sure all camcorders are either in DF (dropframe) or NDF (non-dropframe) mode.

If you are in a situation where it is too difficult to wire these genlock and timecode signals together there is another method that may work well enough. Set the master camera to time of day or just reset it, keep all camcorders in free run mode. Just prior to the event taking place, momentarily plug the master camera’s time code output to each slave cameras input. This will lock everyone to the same free running time code. As time goes on, the time code will drift slightly, but may be good enough for postproduction use. If time allows, the slave cameras can resync time code every so often and minimize timecode drift.

It is also a good idea to practice time code and genlocking in order to verify that all your video cables and connectors are good and the cameras genlock properly. The side mounted genlock and timecode connectors can get damaged enough to become inoperable. I know because we fix enough of them. Happy shooting.

God Bless,
Roger Macie 
 

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