Sony FX3 with timecode-cable: delay of 2-3 frames

[Sound]

I tried to sync the Sony FX3 via the new timecode cable, which connects to the sony multi port and translates an LTC-timecode to Video timecode.

I connected a Ultrasync One via the two connectors to an audio port and to the cable so the signal is absolutely identical.

I waited for a few seconds for the camera to find the timecode and then recorded in 50p (for europe).

Now when I try to sync in Tentacle Sync Studio there is a constant shift of 2 frames of the video-timecode compared to the audio timecode.

Does anyone know what's going on and does anyone have the same experience?

[The Documentary Sound Guy]

Presumably, there are two frames of video latency that isn't being compensated for in camera.  It wouldn't be the first camera to have less than perfect sync.  It's also quite possible the video latency changes with internal camera settings (particularly frame rate & resolution), so it won't always be a consistent 2 frames.

I'd be inclined to trust the timestamp over the audio LTC track, but you'll have to do your own testing to confirm which (if either) of the two timecode methods is correct.  I would also do a clap test using the internal mic on the camera (if there is one, or find a "plug-in" mic that is compatible) to try and establish whether the audio and video are properly in sync within the camera itself.

I'm also not familiar with Tentacle Sync Studio, so I don't know how it is syncing your sources by default, but you'll need to know whether it's trying to sync waveforms or timestamps, and you should verify manually that the sources are actually in sync before reading too much into the results in the screenshot.

[Sound]

Thanks, audio LTC is perfectly fine as always. I did a clap test an it’s the usb adapters problem. There are lots of other users warning about the issue, for example in the comments here: https://www.newsshooter.com/2022/07/14/how-timecode-sync-works-with-the-sony-fx3/

 

and even tentacle has a warning on it’s webpage:

NOTE:

We have current information from Sony that there may be deviations of +/- 1 frame or even more when using the Sony timecode adapter cable VMC-BNCM1 with external timecode generators. Therefore we recommend the timecode synchronization via the 3.5mm Mic input as audio timecode if this is feasible in the workflow. 
 

https://tentaclesync.zendesk.com/hc/en-us/articles/4403308580241-How-can-I-sync-my-Sony-FX3-camera-
 

But no statement from sony ever. Although this could destroy a production: not fair for a camera from the „professional“ cinema line.

 

Could anyone make it work?

 

[Sound]

10 hours ago, The Documentary Sound Guy said:

Presumably, there are two frames of video latency that isn't being compensated for in camera. 

You are right! I set it from H264 to HEVC - both 50p - and now the delay is one frame. This is one thing that could definitely be fixes in FW, but there have been loads of updates since the cable came out and nothing happened.

[Sound]

I guess the only solution right now is to add a -0,05 sec shift in tentacle to get it in about the right ballpark. It shifts slightly between clips but this for me seems to be the best middle ground for HEVC 50p 422 10 Bit. With audio Timecode there is no shift at alle, I guess Tentacle compensates when the timecode signal does not exactly meet the start of a new frame that's been recorded. I didn't test it extensively though so I wouldn't rely on it right now. I will continue to shoot with Audio Timecode plus USB time and will be comparing if there is any massive drift when the Timecode box stays connected to the camera via VMC-BNCM1. Still its not a good sign that tentacle warns you about using this cable.

[Sound]

Now I thought to give the timecode cable a try again. But instead of a fixed delay its now drifting between zero and two frames. Has there been a solution yet or do I stell need to feed audio tc to sync accurately?

[Bouke]

What I dont quite get, I see audio TC's with frame numbers higher than 29
That is unsupported in LTC.
So, to make that happen, the software has to calculate the found LTC to seconds and back to HH MM SS FF (I take it that's what Tentacle software does, my LTC convert certainly does this.)
For that it needs the framerate of the LTC. That can be autodetected, but if that goes wrong (eg, it's very hard to distinuish 23.976 from 24), the math could be off.

Are you sure the LTC is at a 'logical' rate? I would use 25 in your case.

No clue why you shoot 50 unless you expect slomo on 'any' shot, or want to go to interlaced video. (shorter shutter time makes for less motion blur, more strobe like image)

 

 

[Sound]

Thanks for your help Bouke! I am always shooting 50p in Europe as I have to deliver 50i for broadcast in the end. 25p is not allowed. So video is set to 50p and all timecode boxes including TC out on the Zoom F6 is set to 25. This works perfectly fine with audio LTC, but its a Sony issue with the adapter, which should convert audio to a "real" timecode..

[Bouke]

Bullshit, 25P IS allowed in Europe. (I've send thousands of hours to European broadcasters, mind you, I work in Post, not in sound), but only in a 25I container! (What do you think, movies shot at 24 speeded up to 25 become 'interlaced' due to whatever magic?)
An 'adapter' can be anything, but not a 'randomizer'. The 'random' part worries me, that makes no sense.
(I can imagine an delay due to the complexity of the image, so the more complex, the more time the image takes to hit the output, but that 'should' be an easy test..)

 

 

 

[Patrick Tresch]

On 12/26/2023 at 3:17 PM, Sound said:

Thanks for your help Bouke! I am always shooting 50p in Europe as I have to deliver 50i for broadcast in the end. 25p is not allowed. So video is set to 50p and all timecode boxes including TC out on the Zoom F6 is set to 25. This works perfectly fine with audio LTC, but its a Sony issue with the adapter, which should convert audio to a "real" timecode..

? You can shoot 25p and do a 50i extraction. Wich is called Psf 

[touchdown]

Does anyone know if this Diety cable has the same timecode delay issue as the Sony one? https://www.bhphotovideo.com/c/product/1756299-REG/deity_microphones_dts0308d65_c23_timecode_cable_for.html