Pro Tools Reference Guide818
29.97 fps Non-Drop Rate Not Recognized
29.97 fps Non-Drop is a slightly slower version
of 30 fps Non-Drop time code. When 29.97 fps
Non-Drop is used with color video, each video
frame matches up with each SMPTE frame with-
out having to use a drop-frame coding. This
makes any frame number mathematics much
simpler, since no frame numbers are dropped.
Some hardware and software devices do not rec-
ognize 29.97 Non-Drop as a separate frame rate.
For example, any standard SMPTE-to MTC-con-
verter does not explicitly recognize it. You must
set the convertor to expect 30 fps Non-Drop in-
stead. In fact, many devices that read SMPTE
work acceptably by reading 29.97 Non-Drop if
they are set to expect 30 fps Non-Drop.
Any SMPTE reader that uses the time code num-
bers to make real-time calculations (as Pro Tools
does when it tries to trigger and synchronize to
SMPTE) also needs to know that the frame for-
mat is 29.97 and not 30 fps. Since Pro Tools al-
lows this choice of frame rate this does not re-
ally pose a problem. The problem exists because
many users cannot readily distinguish 29.97
from 30 fps.
Even though NTSC tapes only use 29.97, some
production companies will distribute video
work prints striped with 29.97 fps but mark
them as “30 fps NTSC,” by which they actually
mean 29.97 fps Non-Drop.
By the time you get the tape, you may have no
idea what’s actually on it. Feeding 29.97 Non-
Drop to Pro Tools when it’s set for 30 fps Non-
Drop will result in timing errors of about 1.8
frames per minute, causing audio playback to
trigger out of sync.
Use a Consistent Clock Source
When possible, media files should be played
back using the same sync reference signal they
were recorded with. This assures the closest
match between record and playback sample
rates.
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