Bubu

Feeding the wrong fps to a Alexa Mini

4 posts in this topic

Hi all,

Just wondering if anyone has had the misfortune of feeding a alexa mini wrong fps? I.e. we where shooting at 24 fps but the sound files seem to be at 25 fps for 2 whole days. Wondering how that could have happen.

Does the camera sync? Or does it display somekind of error?

Looks like I might have done just that a couple of months ago, just wondering if anyone has done anything similar..

all the best 

Bjössi.

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The files "seem" to be @ 25 fps TC or they "are" @ 25 fps?  WaveAgent will tell you what the TC flag on the files is.  The camera is not syncing to the external TC (if that's what you did) in any case--it just uses that TC to label the frames it makes under the control of its own clock.  
 Were they shooting "real" 24 fps or 23.976?  In any case, since the Arri clock is so good and presumably your audio files were recorded on a machine with an equally good clock then the posties can do a manual sync, at least, and all will be well.  WaveAgent also will allow you to change the TC flag of your files to any frame rate you want, if that helps.

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BWF files are the same for 24 and 25, as the BWF timestamps converted to TC have no non-drop issue. (23.976 has this 'problem' )

Now, in Avid, you might need to override the 'baked in' speed, so TC matches. But Avid syncs sample accurate based on the SAM (if you turn that on), so it should be no issue.

What CAN be an issue, if you have fed TC to the cam from the bwf recorder, I have no clue what happens then...

I would say, test a couple of clips, if they sync with a 'little' offset, it's an easy fix if the offset is always the same.

If the cam did not lock at all, or the offset differs between clips, it's manual or Plural Eyes....

But again, since it's 24 vs 25, I cannot imagine it's a progressive drift. (That can be compensated as well with a little math.)

If that happens more often? Yes!

One of my clients had his Zaxcom setup for 25, the cam was 25, but LTC on a soundchannel was 24

He used a TX/RC Zaxcom system, where the RX was set to 23.976, so the LTC (on a soundchannel, NOT tc input) was in 23.976. (In this case / piece of hardware, the RX regenerates, it does NOT relay incoming!) This was an easy fix, as there was no slaving, it can be done with simple math.

Another example, today I talked to a sound guy who had a gig in the US, and the DOP refused to tell him the framerate they were shooting (Don't ask why, I have no clue.). He being European, unknowing, set up for 30 fps where they were in fact shooting 23.976. This will probably a 2K screwup from the DP, unless there is a very tech savvy editor, who will curse anyways...)

hth,

Bouke

 

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Thanks for the reply, I know how to fix the problem in post, and it is fixed. I was just wondering if anyone had the direct experience of feeding the wrong frame rate to the Alexa mini. And seeing/knowing what happens. 

Why?

Having a hard time getting info out of the camera crew and the editor. Meanwhile production is busting my nuts.

All the best

Bjossi

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