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SDI Audio and Analog out of sycn

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Rob Tobin
SDI Audio and Analog out of sycn
on Dec 13, 2009 at 7:24:55 pm

I just got a LM-1760W and when I play the audio on the monitor via SDI it is 2 to 3 frames out of with
the the analog audio out via XLR's from a Kona LHe going into a Mackie 1402. I Trust the embedded SDI
audio but the question is why and how do I get them right. If I slip the playback control in FCP from 4 to 7 the audio matches but the computer monitor is way off. I also post on the Kona.
Thanks




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Bram Desmet
Re: SDI Audio and Analog out of sycn
on Dec 13, 2009 at 8:48:33 pm

Hi Rob. The disembedded audio is automatically delayed by the monitor to account for the video processing delay (present in all LCD monitors) so that is in sync down to the millisecond (provided of course that the audio is actually in sync in your source material).

There may be some other factors adding even more delay, but a part of the mismatch between the analog audio and the monitor is likely due to the video processing delay. Adding an offset as you mention is one way to account for this issue. You can also put the monitor into "FAST" video processing mode from the video menu, this reduces the video processing delay by about half. We normally recommend normal video processing mode as this allows the ancillary features like waveform, vector scope, etc. to update faster (real time).

If you only need to monitor two channels of audio you may want to consider using the analog audio out (mini-jack connector) from the monitor as this audio is also automatically offset to match video. Some customers are doing this and find it satisfactory as it takes the guess work out of the necessary offset.

I believe there are some other posts on the COW related to this subject that may be worth looking into for more info/advice.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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Rob Tobin
Re: SDI Audio and Analog out of sycn
on Dec 14, 2009 at 1:47:23 pm

Thanks for the quick response.
I did figure out that taking the de-embedded audio
out from the monitor seems to be correct. I just want to be
sure that this is what a tape deck will see. The off-set in FCP
wasn't a good option as the canvas window becomes way of out sycn.
Your right about the guess work which is why I went for the monitor
before I was analog audio and RGB analog HD for monitoring while inputting and outputting
SDI. So far I'm happy with the decision will be doing my first job on it today.
Thanks




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Bram Desmet
Re: SDI Audio and Analog out of sycn
on Dec 14, 2009 at 9:24:23 pm

"I just want to be sure that this is what a tape deck will see."
Yes, absolutely. The disembedded audio from the monitor is only delayed by the amount of video processing delay and pixel response time of the unit, it does not compensate in any other way. So if the audio disembedded by the monitor and the video on the monitor are in sync then they are in fact in sync from the source.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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Ron Cohen
Re: SDI Audio and Analog out of sycn
on Dec 18, 2009 at 1:25:22 am

Bram...

Yes I noticed this too. So - just to be clear - if the audio that plays out of the speakers ON the Flanders monitor is in sync with the video on it, then everything is okay. Correct?

Ron


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Bram Desmet
Re: SDI Audio and Analog out of sycn
on Jan 7, 2010 at 9:41:39 pm

Sorry, I missed this post and just stumbled upon it.

Yes, that is correct. If the disembedded audio coming out of the speakers is in sync with the video onscreen then it is in sync from your source. We delay the audio ONLY by the amount of video processing delay so if there is an audio sync issue when listening on the built-in speakers you would know that there is in fact an audio sync issue in your source.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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Matt Campbell
Re: SDI Audio and Analog out of sycn
on Sep 25, 2013 at 1:58:22 pm

Bram or anyone for that matter, we've recently purchased the BM210, love it BTW, but I'm trying to figure out how to get the audio out from the monitor back to my Mackie 802 for monitoring.

I'm feeding the FSI via HD/SD-SDI, no problem there. Decklink audio out from I/O to 802 ch. 1-2. I use this for mixing and general editing. But if I want to be sure I'm in sync and for client playback, Kris mentioned I should run the audio output via 1/8" from FSI into 1/4" TS ch. 5-6 on Mackie. I may have mixed up what he mentioned but I believe my thinking is correct.

Anyway, problem is, I can't get this to work right. What am I missing? And is this the proper set up for monitoring playback of both audio and video via the FSI and my KRKs for client review.

OSX 10.7.5 with a 3.39 Ghz Intel Core i7 on a built up Hackintosh
16 GB of RAM with OSX on SSD, (2) internal HDDs RAID'd 1 for project files and External RAID 5 for all project assets (media, GFX, stills, etc.)


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