What's the GENLOCK for?

[Edwin Hernandez]

Excuse my ignorance.
Since the genlock figure was almost extinct in the firewire DV world, I just don't have a clue on what do I need the genlock for. Anyone please?

[A. J. deLange]

Genlock is used to synchronize multiple cameras with each other and with audio equipment. If one is going to switch suddenly between cameras or dissolve between them in real time i.e. with a switcher as opposed to in post it is necessary that the frame rate, line rate and color burst be running at the same rate and be in the same phase - at least that's the way it is with analogue video. With digital it is necessary that the sampling rates be synchronous i.e. that the first sample in a frame within the signal from the first camera be aligned with the first sample in a frame from the second camera. That takes care of everything as there is no color subcarrier in digital.

If audio sampling rate in a separate device (DAT recorder for example) is genlocked to the video then sound and picture will stay in alignment no matter how long the take.

Another aspect of this is when a remote camera is connected to a studio or network. If that remote camera is in the middle of a frame when the newtwork is at the beginning of one there would be a huge hiccup if that camera were put on line. Thus remote cameras are tied to studio sync, via genlock, and the studio sync derived from the network sync.

[Chris Hurd]

Basically speaking, genlock on all video devices used on a shoot (cameras, title generators, VTR's etc.) provides a locking signal which keeps all of the devices in phase with each other... all cameras begin their field scanning at the exact same moment, enabling seamless switching at the video mixing console. If you've ever seen a "rolling black bar" on a television or video program, that's caused by unlocked, out-of-phase signals mixing with each other, thanks to an out-of-tune or altogether absent genlock. If I recall correctly the rolling black bar is the vertical blanking interval sweeping through the picture for thirty or sixty frames or so, which you're not supposed to be able to see normally.

(Edit: Aack, I posted right on top of A.J. there. D'oh!)

[Edwin Hernandez]

Thanks.

I remember that in the old days of SVHS editing, we used to have a genlock for using with the titler.

Nowadays, will it only be used for live recording, live broadcasting or close circuits? Nothing to do with post anymore?
-EDWIN

[Jean-Philippe Archibald]

A.J. and Chris must be using GENLOCK to be so in-phase, synchronized in their answers with each other...

[Yi Fong Yu]

geek humor =).

so in another words, if you're have no need to synchronize anything, you don't need genlock @all =).

[A. J. deLange]

That's right!

[Steven Blye]

I just wanted to point out that many (judging by my encounters) have been waiting for the ability to produce 3D (stereoscopic) works. To do this one must have two cameras whose screens write in sync, but this has been impossible with the 3 chip dv camcorders that have been produced up till now. I am thrilled that finally a camcorder of this quality is now within my reach. Unfortunately I need two, but I can always rent one if that is impossible, having one to become familiar with. It has been a long wait entailing many work arounds, but I've now seen a true barrier to my work fall. So, there are some independent filmmakers who have now been included in the revolution.

You may have noticed that several big name directors are intrigued by 3D (James Cameron, George Lucas and Robert Rodriguez) and there is a renewed push in the industry to outfit threatres for 3D to help spur the digital revolution in film and lure people back into theatres. I hope soon that 3D will become part of the digital film festivals and independent 3D films will find an outlet.

[Walter Graff]

Don't forget that without genlock you can't properly sync Time code between two cameras either.

[Steven Blye]

Could someone illuminate how one accomplishes Genlocking of the cameras when not in a studio setting? They both have Genlock in I believe. If there a device the slaves both cameras in the field?

Thanks

[A. J. deLange]

The camera apparently has Genlock In only. Genlock out would be the composite video output of the master camera. This would be connected to the Genlock In port of a slave (or slaves). Multiple cameras can be daisy chained but the one at the end of the chain will be beind the master by the total length of the cabling (about 2 nS per foot). Alternatively one can buy time base generators with extra stable crystals which can serve as the genlock source for one or more cameras in the field (battery operated). If the cameras are all connected to this device with cables of the same length they will be very nearly exactly in sync.

[Nick Hiltgen]

Steven, amoongst other options one way to do this in the field would be to use an item called a "clockit" box. These recieve timecode from a hero camera and then lock the time code into the boxes. Once the boxes have the timecode from the hero camera attach them to the TC IN port on the slave cameras. The boxes are about the size of a deck of cards and usually are held on by velcro.

[A. J. deLange]

Just so we are clear on it, time code is a separate signal unless the camera generates or is receptive to VITC (Vertical Interval Time Code) which is, as the name implies, time code whose 1's and 0's are placed in the video lines during the vertical retrace interval and which can, thus, be carried in the genlock signal. The less sophisticated form of time code is LTC (Longitudinal Time Code) which is an audio bandwidth signal (it can be recorded on an audio track). The BNC connectors on the XL H1 clearly expect LTC and generate LTC. Note that the XL2 generates LTC (but not VITC AFAIK) and this signal is available from the LANC port (but in LANC format - it must be converted to LTC format before it can be recorded on an audio channel). To genlock a set of cameras and have them all recording the same time code requires supplying both the genlock and the LTC signals - that's why there are 2 BNC's on the XL H1. There are several devices designed to generate genlock and and time code, to accept LTC and genlock and repeat LTC, to generate genlock from LTC etc.

[Steven Blye]

A.J. and Nick, thanks for the info.

So, a clockit box perhaps would not work with the XL H1? If I'm understanding correctly, because of the sort of time code.

From A.J.'s info - I could either genlock both cameras with one device, but the timecode wouldn't be in sync, or get another device that genlocks and locks timecode as well. Hope I am understanding you correctly.

If you would have any suggestions as to the specific devices/products you would prefer in this situation, that would great as well.

Thanks again.

[Nick Hiltgen]

I may be mistaken but i believe that the clockit boxes have a genlock port as well. AJ is definitely more knowledgeable on this then myself though.