Workflow for Pro Tools and 4K Video Camcorders to Avoid Drift

[Asaf Blasberg]

Hello,

I film lots of concerts using Panasonic 4K DVX200 camcorders. They all record 4K video with PCM uncompressed audio at stereo 48 kHz using the built-in mics of the camera.

Many times I get Pro Tools sessions from other venues. I then very easily create an AAF file to send to Avid Media Composer. The Avid very nicely puts each audio file in its own audio track so I have full control.

I also put my video track along with my audio track (the camera's built in mics). What happens is over time, there is drift and the audio/video go out of sync. I made sure to line them up perfectly from the beginning.

My understanding for the reason is that all devices have to be based on the same clock to avoid this issue.

Is my understanding that the Avid Sync HD box is the only hardware which can actually set the master clock based on LTC timecode (my camcorders have LTC timecode BNC connectors). I also have a Mosegear QBit timecode generator.

I realize that in the audio world, people use word clock to sync up all the audio devices, but in my case i have video camcorders and the venue's audio engineer uses Pro Tools to create the multitrack audio recording for me so obviously two different devices use two different clocks.

He gives me the audio files at 48 kHz, so the sampling rates of the laptop recording are the same as my camera.

Let me know what you suggest - obviously the Sync HD box is $2k but money isn't the problem, just want to make sure that this is the box that solves this issue. I was also told by MOTU that they can also set the master clock based on LTC timecode (it's in their manual) and quoting from the manual it says:

"When you choose the LTC clock mode setting, the audio phase lock engine in your MOTU interface resolves to the incoming time code. This ensures
that audio passing through the interface remains resolved to time code and won’t drift over time, as long as the audio is coming from other sources
that are also resolved to the same time code. This also ensures that audio recorded by DAW host software on a connected computer, or audio playing back from the DAW, will remain resolved to time code and won’t drift over time, even when restarting or cuing the source time code."

If I can use my QBit generator as the master and then *feed* the MOTU device the timecode as a slave, as well as the same for my video camcorder, in theory i should have no drift. Is this correct? I don't have the MOTU box so i haven't tested it.

Thank you very much for your help in this and sorry for the long long post :)

Sincerely,
Asaf

[DetroitT]

Everyone at same frame rate?

[Asaf Blasberg]

Yes DetroitT, same eveything

Frame rate = 29.97 Drop
16bit
48kHz
Thanks,

[JuelzB]

Found this article quite informative on the subject: https://www.bhphotovideo.com/explora...why-it-matters

[Asaf Blasberg]

It is very interesting indeed! Yes, unfortunately it deals more with the video side than the audio side. My workaround for now is to just "stretch" the audio to the left to get it back in sync...

[JuelzB]

Maybe this could help: https://www.soundradix.com/products/...post/#features