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
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.