R1MX timecode sync & drift questions

[T_Freundlich]

Hi all,


I'm shortly embarking as DP on a feature-length documentary for which I'll be shooting a lot of footage that needs to be timecode synced to an audio recorder. On my previous projects I haven't had a need for timecode sync so would welcome some pointers.


I'll be shooting on my R1MX so the current working hypothesis is as follows:


1. Mount lockit box to camera
2. Jam camera and audio recorder (exact model TBC from sound recordist) to lockit box
3. Leave lockit connected to camera with cable and with Jam enabled in the R1MX timecode options
4. Occasionally re-jam the audio recorder (every few hours?)
5. Also record scratch audio as backup directly to camera


Questions:


- With the above setup, the camera should automatically stay synced to the lockit, even through battery changes, right?


- A couple of people I've spoken to have mentioned issues with timecode on Reds drifting, sometimes even with a lockit connected. I tried some searches on the forum but all the results seemed to be really old, like from 2009. How common an issue is this? Assuming everything is set up and connected correctly as above, what is a reasonable expectation for frame sync accuracy over, say, a day of shooting? Anything else in particular to be aware of?


- (How) would you incorporate genlock into this setup?


- And, finally, what happens to the timecode if I'm jam synced to the lockit but shoot some varispeed? Will the timecode of the first frame be correct but that of the remaining frames incremented sequentially as if they had been shot at normal speed?


Thanks in advance!

 

[Marc Wielage]

Generally the sound department becomes the Timecode Master for the entire project, so the timecode jam box on the camera (like a Denecke SB-T or an Ambient Lockit box) gets jammed from the audio recorder, not vice versa. The TCXO crystals in the recorder and in the SB-T or Ambient boxes are pretty much good for 1-frame accuracy in a 6-hour period, so I typically re-jam the slate and SB-T at lunch or halfway through the shoot, whichever comes first.

In varispeed, it all goes to hell, the camera ignores the external TC, and the timecode reverts to 00:00:00:00. But that would most likely not be sync sound anyway, so it kind of doesn't matter.

Note: whenever possible, shoot a workflow test so that you can verify that picture and sound will stay in sync with no problems. A timecode slate helps quite a bit.

 

[Gunleik Groven]

Re-jam at lunch, is a good idea.
Loong takes wil slip, unless genlocked, but there are easilly issues with genlocking UNLESS YOU HAVE TESTED THE WHOLE THING PROPERLY.

Generally I just try to avoid genlocking.

 

[T_Freundlich]

Great, thanks guys - this is very helpful. So, to summarize, updated workflow plan is:

1. Mount lockit box to camera
2. Jam lockit box to audio recorder
3. Jam camera to lockit; leave lockit connected to camera with Jam enabled
4. Repeat 2&3 as necessary
5. Also record scratch audio as backup directly to camera

...right?

A TC slate would be great though I have a feeling that in this project slating won't really fit into the flow of things... But yeah, will be sure to do some testing beforehand.

 

[T_Freundlich]

Loong takes wil slip, unless genlocked, but there are easilly issues with genlocking UNLESS YOU HAVE TESTED THE WHOLE THING PROPERLY.

Generally I just try to avoid genlocking.

Gunleik, can you elaborate on what kinds of problems you have run into? I know for sure I'll have some long (1hr+) takes on this show, so trying to figure out if genlock would be useful or not.

So if I understand it correctly, all the jam sync does is ensure that each clip starts with the (more or less) accurate time code, but after that, once the take is rolling, the lockit box has no effect and the camera is dependent on the accuracy of its internal clock. Which will of course eventually drift. For the single-camera, single-recorder setup outlined above, would genlocking the camera to the lockit box help keep more accurate sync, or does it make no difference unless the audio recorder is also genlocked to the same TC source?

Enlightenment appreciated, as always!

 

[T_Freundlich]

Answering my own post.. but just to avoid propagating incorrect info, I have just been advised that the camera does in fact follow the timecode fed by the box also while rolling.