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  #1  
Old 06-11-2006, 10:06 AM
pindebraende pindebraende is offline
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Default This may be a stupid Q about sync.....

But I have to ask it anyway.

Here is the deal....

Im having a quicktime movie running on my second HP1740 LCD monitor and everything looks good. No sync issues or anything, and no movie offset either. The dinosaur roars are in perfect lipsync
But then I started thinking about all the great post I have seen on the DUC concerning sync and LCD and plasma displays.

My question is. If I dont see any drift, do I still have a problem?

Sorry for being an ignorant!

Regards

Pindebraende
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  #2  
Old 06-12-2006, 12:36 AM
Starcrash Starcrash is offline
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Default Re: This may be a stupid Q about sync.....

As far as I'm concerned, any latency associated with LCD display is negligible. In fact, I've never heard of it being an issue except on this forum. Major Hollywood feature films are edited every day using Quicktimes that are internally synched in PT on LCD displays. There are many other far worse sync bugaboos out there than LCD latency. Not a stupid question, though.
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  #3  
Old 06-12-2006, 01:05 AM
Eric L Eric L is offline
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Default Re: This may be a stupid Q about sync.....

Quote:
As far as I'm concerned, any latency associated with LCD display is negligible. In fact, I've never heard of it being an issue except on this forum. Major Hollywood feature films are edited every day using Quicktimes that are internally synched in PT on LCD displays. There are many other far worse sync bugaboos out there than LCD latency. Not a stupid question, though.
I could not disagree with you more. It is far from negligible. I had foley delivered to me that was cued on an LCD panel, then recorded while the artists viewed a different LCD projector and then it was cut on a third different LCD. By the time I got in on my stage the footsteps were silly out of sync!

Worse, when we went to try to pin down the culprit, nothing was consistent because of the varying response of the different LCDs.

It is something to be aware of and it should be measured and dealt with. Many posts on the subject for your review if you search.

By the way, many "Major Hollywood" tv shows are broadcast out of sync, but that doesn't make it right. Guaranteed that whatever "major Hollywood feature" is synced via an LCD panel, it is being adjusted back into proper sync later by someone else using the correct gear. Just because some PT jockey thinks it looks good, doesn't mean it is.

I'm sure Richard Fairbanks will be along shortly to address this subject as well.
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  #4  
Old 06-12-2006, 02:15 PM
Starcrash Starcrash is offline
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Default Re: This may be a stupid Q about sync.....

Eric,
I certainly respect your opinions and your experience, but this information doesn't add up. When you say "silly out of sync", you must mean more than a frame out. Any less than 1/2-3/4 frame gets debatable especially when you're talking about foley FS. How is this severity of latency possible from LCD display response time? Are you referring to the LCD response time or other hardware issues? I would be looking at DV firewire, video card, or PT video offset as a more likely culprit than LCD response time. It's hard for me to believe that a foley artist's performance is going to be affected by an 8ms latency. In my experience cutting foley, the first couple footsteps of a cue are often out by a frame or two due to human latency (reflexes). Of course results vary depending on the talent and experience of the artist. Like I said before, you have my respect and I invite you to correct me if I'm wrong. Where I work, there are no adjustments made for PT sessions cut using an LCD display. Editorial department is expected to deliver material that is in sync and LCD latency has never been an issue before.
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  #5  
Old 06-12-2006, 03:08 PM
Richard Fairbanks Richard Fairbanks is offline
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Default Re: This may be a stupid Q about sync.....

Many of you know I am pulling back on my posts these days, but now I've been dragged in again even if not by Starcrash.

Nothing against you, Starrcash, but I do not understand why there is any argument at all! LCDs all have latency, some more than others, with typical values between 1/2 and 2 video frames, depending on all kinds of things. Plasma screens seem to be roughly double. I am NOT talking about "drift", I am talking about a more or less steady time delay from when the computer spits out picture data to when your eyes actually see the images. If there has not been more mention of this elsewhere, it points to how aware members of this group are! Actually, I'm not sure I agree with you, I have seen LOTS of discussion in home theater groups and among professionals. There are too many variables, with many manufacturers products along the way, to simply trust that everything is just right. If the errors were always less than a frame then I doubt many of us would have ever worried about them.

If you sincerely believe you do not have any sync problems, who am I to argue?
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  #6  
Old 06-13-2006, 01:11 AM
Eric L Eric L is offline
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Default Re: This may be a stupid Q about sync.....

Hi Starcrash,

By silly out of sync, I mean frames out. Not one, not two, but 3 or more. This was not a matter of slow artists. That is another problem all together. You are confusing the Pixel Response time with the inherent delay of the device. They are not the same. 8ms pixel response time is simply how long it takes for the pixel to go from grey, to a color, and back to grey again. The faster the time, the less blurring or ghosting you see. Basically, the pixel needs to go on and off faster than the picture scan rate in order to prevent ghosting.

Many manufactures build in a buffer circuit to aid in the processing of this data. This buffer is the culprit of our sync problems. There is no standard, and many manufacturers will not publish the amount of delay, some will not even confirm that it exists. But it does. So much so, that some LCD tv manufacturers have implemented an audio delay circuit to make up for the video delay. Unfortunately, this only works with the built in speakers.

Luckily, this delay can be measured (thank you Richard) and accounted for with movie offsets or audio delays. I have not encountered any LCD technology that does not have at least 1 frame of delay. Most of the time it is much, much more. I have a Dell LCD that I love. But it is noticeably slower than my crt video monitor. When I watch the movie window on the Dell and the video on my video monitor it is a big difference.

Either the delay of your LCDs have been accounted for by an offset, or someone else is fixing your sync done the road. Because it will be out of sync.
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  #7  
Old 06-13-2006, 01:30 AM
Kuba Pietrzak Kuba Pietrzak is offline
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Default Re: This may be a stupid Q about sync.....

Guys,

I am no so sure, but I can see a little bit misunderstanting here...

There is a difference if LCD display is conntected to computer as just the second screen that spreads the desktop, and if LCD display is conntected to any NTSC or PAL video out port (cannopus, fuse-x, etc, etc);

if you connetct LCD via NTSC/PAL port you will receive latency (because the device needs time to do rescalling);

I am not so sure, but if you see QT as a float movie window on your second monitor there should not be a noticeable latency (there is no need to rescale)...

Correct me if I am wrong

Best
Kuba
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  #8  
Old 06-13-2006, 09:55 AM
crna59 crna59 is offline
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Default Re: This may be a stupid Q about sync.....

Does this latency differ from VGA vs. DVI connection?

Regards,
Bruce
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  #9  
Old 06-13-2006, 10:25 AM
Richard Fairbanks Richard Fairbanks is offline
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Default Re: This may be a stupid Q about sync.....

Quote:
...if you see QT as a float movie window on your second monitor there should not be a noticeable latency (there is no need to rescale)...
Hi, Kuba! No, this is definitely NOT always true. I have a 17" LCD as a 2nd desktop monitor on my G5, connected through the G5's DVI port. A standard def DV movie playing from Pro Tools in a floating window (no firewire, no video hardware, movie offset set to zero) plays between 4 and 8 quarter frames later than Pro Tool's audio on that monitor. Drag the window across to a 22" cinema display and the error drops to between 1 and 3 quarter frames. The range of error (1-3 or 4-8 qtr frames) is a slowly changing drift between the low and high numbers, caused by each monitor's refresh rate not genlocked to the video frame rate.

This has been stated here and on my website for quite some time. Everyone I know who has actually checked has seen a similar result.

An error between 1 to 3 quarter frames is not too bad, you could probably ignore it if you had to, but an error between 1 and 2 full frames is not acceptable in my opinion.
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  #10  
Old 06-13-2006, 12:12 PM
Starcrash Starcrash is offline
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Default Re: This may be a stupid Q about sync.....

Thanks for the input Richard. I know that you've thoroughly researched this topic and I'm certainly not here to argue against your findings. The intent of my first post was to respond to a misconception that I think can be easily made by reading some of the threads on this forum. The original poster was asking if an LCD display is a viable option for post because he'd read on the DUC that they caused unacceptable sync issues. I don't think that this is necessarily true and so I pointed out that no one that I work with nor myself have had any problems with sync related to LCD latency. I work at a reputable post-production facility as a sound editor on large-budget feature films. I'm certainly no expert on technical matters so I can only speak from my personal experience.

One more thing that I wanted to point out pertains to workflow and why LCD latency has a negligible effect on how I work. When spotting a hard effect, foley prop, or FS I use sync points and nudge to the correct position. Then I usually check it at 1/2 speed, then full speed. If my display was out by two frames at full speed, it would be hard to not notice the discrepancy. It looks solid at my workstation and solid on the stage. If I told the supervisor or the mixer that I was using a video offset in PT to compensate for LCD latency, I think that they would look at me like I'm crazy.

Lastly, I would once again point out that I'm not looking to rustle any feathers here. I hold the DUC and its members in very high regard especially valuable contributors like you Richard and Eric L. Both of you have helped me directly and indirectly in the past and I appreciate both of you guys. I think I might sit the rest of this one out.
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