time code drift
 

I just worked on my first multi camera field shoot with the XL H1 and everything went great except for time code problems. I spiked/jammed one camera off of the the other and let them free run in the same mode(non drop frame). I noticed after a day of shooting(6 hours) the TC was off by over 4 minutes.

Anybody experience this? If it is not mormal, then I guess a call to Canon is in order unless nothing can be done. If there is no cure to this drift, does anybody have a recommendation for an inexpensive, portable and wireless TC generator and receivers.


Thanks

-Bill

Bill,
Yes it is kind of normal although 4 minutes is a little more than one might expect. the only solution is to keep the cameras connected to timecode and genlock or get the wireless boxes which have sync and timecode. Denecke has some portable boxes but you might want to call a high end film/video sound house Like Gotham Sound in NY for other recommendations. If you can send sound to each camera then it isn't tooo hard to sync them back up even with the drift.
Also don't shoot in 24F DV and expect to use any free run time code. HTH

Bill - I too did a multicam-shoot with two XL-H1s lately, but had a much more positive experience. I had to re-sync after changing batteries (about every 3.5 hours) because the slave cam loses sync after every power-down (this includes standby --> see manual). At the end of each 3.5 hour period, cams were still within a few frames of one another. Did you possibly power-down the slave cam during the shoot?

Edit: I just checked - 3 frames difference 3.5 hours after sync.

HTH,

Ron

Ron,
Are you shooting in Pal? I noticed you are in Basel. 25 Frames is a little easier to make than 29.97..... so here in NTSC land there might be slightly more drift between the two clocks.
Your other comments about powering down and changing batteries are all valid.
We just don't know how good or bad the normal spec for the cameras is.
When Sony first came out with Betacams they said the drift was something like plus or minus 3 seconds per hour on the broadcast units. If you didn't want them to drift then you had to genlock. That is still the case today. Clock technology has gotten better since then but cameras have also gotten cheaper so the drift might end up being a fairly high number for a consumer camera like the XLH1.
At least the portable timecode boxes are being made which wasn't the case in the old days.

Yes, I am.

While 29.97 sounds like an odd number, I don't think that it makes much difference technically. I'm certain that the quartz that's employed for time-keeping oscillates somewhere in the kHz-range, so it should be perfectly capeable of serving both the PAL and the NTSC-world. But of course that's just conjecture...

But your comments made me think of a situation I had to deal with back in the 68k Apple Macintosh days. The processor clock frequency was used there to generate OS-time. If you had lots of interrupts taking place (e.g. disk or network I/O), the clock would slow considerably because it was missing 'beats'. If the Mac was idling, it would stay very accurate.

It could be that something similar is going on in the XL-H1, and this could also partially explain why the cam loses TC-sync after power-down. What camera activity could cause the TC-clock to miss 'beats'? Lots of starts/stops, taking stills, zooming? Did you do anything 'extraordinary' during your shoot that could have exacerbated TC-drift?

I, too, would be interested in a reliable and cost-effective external sync solution, possibly involving wireless transmission. I heard that wireless audio transmitters/receivers can be abused for this, but don't have any first-hand experience.

I am confused. I understood the manual to say that as long as the internal LiIon battery is charged, all settings and Free Run time code will be maintained, even in power down or standby. (last bullet on page 59).


-Bill

Bill,
Don't believe everything you read quite so litlerally. There is a difference between maintaining a free run clock code and keeping it accurate to the precision we would like our timecode recorded to tape. Also there is a relationship betwen the cameras video frames and the timecode recorded on tape which doesn't exist if the camera is off. When the camera is on it has to provide sync to the clock at the rate of its sync generator. If the rate is 1/60 of a second different from clock mode to camera mode then this could be a minute per hour.
As soon as the camera is turned on the clock syncs to the camera for accurate timecode. This could be called a maintaining level of service.

Bill, you're correct in that the master cam will maintain its free run TC quite accurately even through power-downs. However, the slave cam will lose TC sync at power-down (see p.61 of the XL-H1 NTSC manual for details).

Edit: it is unfortunate that the slave cam's free run TC cannot be synced to the master. The synced TC is a different animal altogether and apparently has no influence on any of the slave cam's 'internal' TC modes. Shame!

HTH,

Ron

Oh Well.....I guess I start looking for a wireless TC source and in the interim, I rejam the cameras after every location move, no matter how little time has past.

At least I ran audio on both cameras so I go back to syncing them during the edit the more challenging way!

So much for the easy transition back into video. I have been out of it for about 5 years on the recreational level and 10 years on the professional level.

Thanks for everybody's help. This forum is amazing with all the knowledge and experience of the members. I hope to be back up to speed soon so I could be answering questions instead of just asking them.

-Bill

A possible alternative to wireless are the Ambient "Clockit" products. These are simply good crystal oscillators which can be set to sub ppm accuracy and run for a day on a set of batteries. They can be jammed to TC and supply TC and genlock signals. They will supposedly keep multiple cameras to within a frame over the course of a day.

Aj,
That is a very good suggestion. Cost is about 1000 to 1200 per unit. One per camera. The Denecke unit is around $950. Either way it is a pretty high expense unless you use it a few times a month.
I have a suggestion which might seem odd but it might be worth setting the time of day on the cameras so they are very close before jam syncing the cameras. This might aleve some of the distance between the numbers you get when you turn off the slave camera and it uses its internal clock.

Excellent suggestion, Daniel! This reminded me of an XL-2 Watchdog article I read some time ago:

http://www.dvinfo.net/canonxl2/articles/article11.php

Next time I have a multi-cam shoot, I'll definitely give this a try!

Cheers,

Ron