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How to measure and adjust for sound vs picture delay?


Mark O'Russa
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I've been following the "" thread. page-3#entry233201, Marc Wielage brings up the point about delay caused by display devices:

 

BTW, in addition to the cameras being off, don't forget that all solid-state monitors are also off in that they introduce a small amount of delay in the signal. They're typically at least 10ms off, which is about 1/3 of a frame. So there are sources for sync delays all over the place.

 

 

These delays of just 10 ms are enough to throw off foley, sound fx, and dialogue - anything really. Does anyone know of a reliable way to measure this kind of picture vs sound delay other than this: http://www.pharoahaudio.com/syncheckproducthomepage.html

 

I use Syncheck version 2 and it seems like the appropriate tool, but even Syncheck isn't foolproof. How else does one measure the delay so that it can be accounted for?

 

The second part of the question, how to adjust for the delay, is easy enough in Pro Tools. It has a video sync offset that offers 1/4 frame steps.

 

One other thing to consider - variable delay. Without genlock between Pro Tools video output and the display device, there will be a varying delay between picture and sound. I can play the same 5 seconds of a scene and the timing will look slightly different each time. Using Syncheck will even confirm that the timing jumps randomly. Oh technology...

 

Mark O.

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Syncheck is the best way I've found to see and adjust system timing.  But if anything in the system is not locked to house sync then it will continue to float around syncwise.  The best you can do is know what the limits of the drift are, usually a frame or so either direction for each playback start without being frame-locked.

 

philp

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Syncheck is the best way I've found to see and adjust system timing.  But if anything in the system is not locked to house sync then it will continue to float around syncwise.  The best you can do is know what the limits of the drift are, usually a frame or so either direction for each playback start without being frame-locked.

 

Philip

How does one sync a computer monitor? Does it have to have a genlock connection or can it be synced via a box like the AVID SYNC I/O?

 

In the mix room I work in there is a consumer level projector. The price of a projector with genlock must be quite expensive, and thusly a breakpoint between a very professional setup and less-than-professional setup. I'd bet that media produced in the world is edited and mixed without genlock.

 

TASCAM distributes the Kamesan KS 1017 in the states.

 

http://tascam.com/product/kamesan_ks-1017/

Good find, although pricey at $2k. They also make a bloop light: http://tascam.com/product/kamesan_ks-1018/

 

Before I started using the Syncheck I recall trying to adjust for the delay by taking a picture of the on-screen video and compare it to the big TC window in PT. After using Syncheck I realized how stupid that was. In the absence of genlock, I believe you must have an external device that can detect both audio and video.

 

Mark O.

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??

 

If the pix monitor is being fed by the DAW's computer, what good would genlock do? One frame comes out of the DAW's video port, it goes to the screen. Monitors don't even have a genlock input. The only time you'd need it is if you're taping the DAW's video out on a pro deck… an unlikely circumstance.

 

Most DAWs use the same clock (internal or word) for audio as it does for the video output. A few good ones have play-time sync compensation on the video outputs, to compensate for the video out card or any processing on the projector. (It's an offset applied during play only. When you're scrubbing/jogging, the offset goes away so you can spot accurately.)

 

Now… if you're playing pix on a separate computer or a VTR / HDVR / VVTR etc, and the DAW is syncing via P2, then genlock on the video device makes sense (but they call it reference sync). If the separate pix device is continually chasing the DAW's output code, genlock is also not needed.

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To have real frame edge sync that holds and starts playbacks consistently in sync the source of the video (a computer's video card) and the word clock of the audio device (DAW) should be locked together, pref to house sync.  Other methods produce "ok" or "kind of" sync, but the picture sound relationship will be slightly diff on every playback, usually within a frame, sometimes more.  A Syncheck can show you this happening on an unlocked system.  It can also show you the delay etc caused by video cards and monitors (all flat screen monitors have at least one frame of latency).

 

philp

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Mark O: " although pricey at $2k. "

not for what it does, and for those who need it...

 

Correct, and wouldn't the solution be to rent one for the duration of the production.  It would probably cost the same amount to rent as to buy outright, but then it's easier to justify...

How difficult is it to persuade the usual suspects to get a useful but not often used piece of equipment into their rental inventory?

Tom.

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