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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Epic audio sync issue

Dave Weber

Dave Weber

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I know it's out there but I can't find the thread.

Shooting 23.98, with an ambient ACL204. Feeding 1080p. The audio is about 3 frames off from video. Any ideas or is this a bug?
 
Brian Ferguson said:
Is it off in the files or while monitoring live, or both?
Click to expand...

On the SSD the files were perfect. We were also recording via Aja box and that is where the 3 frame slip was happening. At the end of the day it was no big deal but I want to know what's up. I want to be able to explain why it is happening.
 
Is the 3 frame offset consistent, or is intermittent? Is only the audio 3 frames out, or is it timecode as well? Is audio ahead or behind? (In my experience with digital cameras, it's typically ahead.)

If it's consistently 3 frames out, just slip it in the edit timeline and move on.
 
We lost a whole night shoot with stunts & VFX because of sync . It seems that there is a bug of some sorts that nobody seems to want to talk about, where when you have sync/genlock into the camera (this waas at 25p) the camera loses frames rendering the footage unuseable.

Red are aware of the latter issue and I am afraid to say that while helpful in pinpointing the inital issues, the subsequent lack of response from them to our insurers has been rather deflating as I had to push very hard to get our production to use the Epic.

However, as far as the audio sync goes, I have 2 x Pix running on the current job, different kit but same principal and that kit has the option of timecode offset as the signal out of the SDI can arrive a couple of frames later than that of the actaul SSD recording - I don't think this is necessarily a big deal, however the more serious complication is if you have got genlock into the camera as well as timecode.
 
As I said before, the files on the SSD cards were perfect. We have recorded for comps via sdi in the past and the files have been perfect but with the newest firmware build it seems that something is different. Like I said it really was no big deal in the end. I was just wondering if I had missed something in the setup. In the end, the SSD files were perfect and all is well. Thanks for your responses.
 
Dave Weber said:
As I said before, the files on the SSD cards were perfect. We have recorded for comps via sdi in the past and the files have been perfect but with the newest firmware build it seems that something is different. Like I said it really was no big deal in the end. I was just wondering if I had missed something in the setup. In the end, the SSD files were perfect and all is well. Thanks for your responses.
Click to expand...

Thats why I asked where the delay was Dave. You know the R3D files are great so it is a processing delay on set.

While monitoring, processing digital files can cause small delays. It may well be the pulldown introduced in the video out, this problem existed way back to the Sony F900. There are some small cheap audio processors that you can tweak delay in. Like the Behringer Shark DSP110 http://www.behringer.com/de/Products/DSP110.aspx

You are adding 6 frames a second if you are monitoring in 29.97 (like via HDMI). Video assist guys were bringing delays in the early days of HD for this reason. I have had this happen in the edit bay when the audio and video went down separate paths. Are you trying to take the audio out the embedded HD-SDI out? I bet if the monitoring path included this you would be a-ok! It is the same pipe, my guess is that you are taking the audio out and video out separate and that is the delay. If you have a solution to handle the SDI Video and Audio in the same box (guessing that you are not currently) that may fix the problem.

If I listen to the Epic audio off the headphone out there is a delay to live because of A/D processing if I listen off of my mixer there is no delay. I check the headphone out to make sure it is good but switch back to the mixer output to keep from hearing the weird audio delay echo. If you are taking audio feed from from the sound man and then syncing it to the video out from the camera video out there is another time offset. The camera maximizes its efforts to get the camera recording correct and the video and audio out is a separate process for monitoring.

Good Luck!
Brian Ferguson
briferg.com

Just a guess that audio is 3 frames ahead of audio now that I think of it! The picture lags because it has to go through the camera and the audio has a shorter path no matter what. I really believe the embedded HD-SDI is always the cleanest solution for a a couple of reasons. Picture and audio should be delivered as in the R3D files -together, and you will HEAR much more accurate audio monitoring, bypass the cameras limited audio outputs. This is a big deal.
 
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Also if your camera files are correct your Ambient is absolutely doing its job! Do Not Change a THING!
The MAIN thing is that you have sync on your R3D's!
Please everyone look at that first and not change anything if that is correct. Clean camera files are the Benchmark and all outside of that are small issues to be solved.

On set monitoring issues can be solved but please do not let these issues cause you to make a change that F's up your R3D's!
There are a dozen on set monitoring reasons for what you are experiencing. I have a background in camera, audio and post. So I have seen this happen in multiple different ways. First thing is the integrity of the camera files. All else is secondary. Red might have changed a small video or audio output parameter on a build but as long as the camera files are solid that is not a concern. Really it only tells me they have done a much better job of monitoring outputs previously because this is an ongoing HD output problem since Sony released the F900! Which I was lucky enough to get my hands on early because of Oakley and Jim.
 
Yep, what Brian says. Quite a few cameras out there have monitoring issues where audio gets ahead of picture. This is not a Red-specific problem.

I'm glad that Dave was able to solve his problem and the original files were fine.
 
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