User`s guide

Chapter 24: Time Code Synchronization 365
Any SMPTE reader that uses the time code
numbers to make real-time calculations (as
Pro Tools does when it tries to trigger and
sync to SMPTE) also needs to know that the
frame format is 29.97 and not 30 FPS. Since
Pro Tools allows this choice of frame rate
this does not really pose a problem. The
problem exists because many users cannot
readily distinguish 29.97 from 30 FPS.
More importantly, some production com-
panies 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 converters need to be turned off and
turned on again to be able to recognize the
new frame rate.
Use a Consistent Clock Source
A sound file should be played back using
the same peripheral and sample rate it was
recorded with, if at all possible. This assures
the closest match between record and play-
back sample rates. For example, if an audio
file was recorded at 44.1 kHz with the
Pro Tools Audio Interface then the Sample
Rate should be set to 44.1 kHz during play-
back with the Audio Interface as well.
On a Macintosh, Disable AppleTalk,
Network Connections, Screen Savers,
and Power Saving Features
These types of software can cause the Mac-
intosh to ignore MIDI data (such as MIDI
Time Code) coming into its serial ports.
Make sure AppleTalk is inactive in the
Chooser, disconnect AppleTalk cables, and
remove any INIT-based network software
from your System Folder.
On a Windows Computer, Disable
Screen Savers and Power
Management Features
These types of software can cause your
computer to ignore MIDI data (such as
MIDI Time Code).