Re: Dropframe Time Code calcs question

On Aug 24, 7:15 pm, Boomboom <compre55...@xxxxxxxxxxx> wrote:
How come some assistants or DOPs will set the cam to, let's say, 24p
and the Denecke to 29ndf ? One told me "it's because we're not doing
"real" 24fps". I can't quite get it.

Even though HD is theoretically a totally new broadcast standard,
completely independent of all the NTSC pull-down, drop frame, non-drop
frame blah blah blah, in practice many (most? all?) HD cameras still
slow down the picture by 0.1%, so the video can be easily
downconverted to standard def and broadcast at 29.97fps. So, when
recording at 24P, the camera is actually recording at 23.976 fps.
Further, many cameras cheat when recording 24fps, by actually
recording at 60i (which is really 59.94 fps) or 30p (which is actually
29.97 fps), and using frame pulldown when exporting.

So to maintain sync with the camera, you need to set the slate to
29.97 fps.

And if I try to sync my mics (Zaxcoms IFB100) by jamming with the cam,
I always end up a few seconds too fast after an hour (real run tc) ?
That sounds about right. If your Zaxcom is running at exactly 30fps,
and the camera is running at 29.97 fps, then after one hour your mic
will have counted 108,000 frames (30 x 60 x 60), but the camera will
have counted 107,892 frames (29.97 x 60 x 60). That makes a difference
of 108 frames, or roughly three and a half seconds. Set your mic to
count drop-frame and it'll match perfectly (well, within the accuracy
of the clock, that is).

BTW, a technical aside: The slow down came about when television
engineers were working on a broadcast standard that would be able to
overlay a colour TV signal on top of a B&W signal, without affecting
the B&W sets in existence. There were about 4 parameters involved. The
committee could keep the TV signal at exactly 30fps and tweak one
parameter, or slow it down to 29.97 fps and tweak the other three
parameters. We all know which route they chose. <sigh>

Martin, if I come across a time machine, you're riding shotgun.

--
Jim

.

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