DigiDesign Pro Tools Reference Manual page 710

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.
Be Careful When Changing Frame Rates
If you change time code rates in the middle of a
session, many SMPTE-to-MIDI Time Code con-
verters need to be turned off and turned on
again to be able to recognize the new frame rate.
Use a Consistent Clock Source
When possible, sound files should be played
back using the same sync reference signal it was
recorded with. This assures the closest match be-
tween record and playback sample rates.
Disable Screen Savers and Power Management
Features
These types of software can cause your com-
puter to ignore MIDI data (such as MIDI Time
Code).
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