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Recording a 30 fps composite signal on a 29.97 fps camcorder

by jensenkk / April 2, 2009 2:06 AM PDT


I am recording an output composite video signal of 30 fps (EIA RS-170) on to a digital video casette recorder (Sony GV-D1000) that operates with 29.97 fps (specified as "NTSC Color, EIA Standard" (presumably RS-170A).

Does anybody know what happens during that process with regard to audio sync and frame dropping?

Audio sync is very critical in my project but it is difficult for me to test on my own. Are there typically inherent mechanisms in camcorders that process and record 30 fps to 29.97 keeping the audio in perfect sync?

Thanks in advance,

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Say again?
by R. Proffitt Forum moderator / April 2, 2009 3:27 AM PDT

Time after time I've put the oscilloscope on the 30 fps signal and found it to be 29.97. Maybe I'm too old to not measure such claims but today after 2 decades plus of electronics design I can't find 30 fps signals.

What exactly is outputting this?

And a good digitizer will not lose sync. Try it. Any other answer would be predicting the future.

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30 fps simply 29.97 rounded?
by jensenkk / April 2, 2009 4:00 AM PDT
In reply to: Say again?

So what you are basically saying is that the whole 30 vs 29.97 frame rate discrepancy is not real in practise?

The output is from a X-ray cinematograph that records with 30 x-ray pulses per second is specified to have a "EIA 170" output, which apparently is a monochrome video standard that runs with 30 fps. If I input this signal to an oscillosope what do I measure to obtain the actual frame rate? Is it a simple periodic signal?

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Can you imagine....
by R. Proffitt Forum moderator / April 2, 2009 4:53 AM PDT

If everyone was made to always say 29.97? It would get tiring and worse.

Again, put a scope on it or just step forward.

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by jensenkk / April 2, 2009 6:25 AM PDT
In reply to: Can you imagine....'s not so much about what people have to say, but how the technique works. That is what I'm trying to figure out and help to make short cuts on that is much appreciated rather than cryptic comments...

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Have we reached the days where...
by R. Proffitt Forum moderator / April 2, 2009 6:46 AM PDT
In reply to: Well...

No one uses an oscilloscope or even knows what one is?

I don't expect you to use one but my background in electronic design demands I use it. I shared where I have never found a 30 FPS signal but now you say I'm being cryptic.

I thought I was very clear on that. Please tell me where I was cryptic.

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For some, 29.97 and 30fps are the same
by Dan Filice / April 2, 2009 7:53 AM PDT

In Broadcast, they are the same. It's the frame rate for video our our NTSC broadcast system. PAL is 25fps, or technically 24.97. The machines know it's 29.97 but as Bob stated, saying 30fps is easier.

Just curious why you are worried about sync issues? If you use video equipment in NTSC, and finish with equipment that is rated the same, you shouldn't encounter sync issues.

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