User`s guide

Chapter 23: Synchronization Concepts 335
Film Speed Differs from NTSC
Video Speed
The new NTSC Telecine master tapes will
always run at 29.97 FPS during post-pro-
duction, so the original production sound
rolls (at 30 FPS) will be too fast, and there-
fore out of sync with the video. Some ad-
justment of this audio may be required.
When spotting audio to video that was
transferred from film to NTSC video, there
are two important terms to keep in mind:
film speed and video speed.
Film Speed Film speed refers to audio that
was recorded and plays back in synchroni-
zation with the film camera. This audio
comes from production reels recorded on a
Nagra® recorder or a field DAT recorder,
and is usually striped with 30 Non-Drop
time code. Film speed audio runs at the
same speed as the film camera or projector,
and is therefore out of sync with 29.97
video.
Video Speed Video speed refers to audio
that is running at the NTSC color standard
of 29.97 FPS. Video speed is 0.1% slower
than film speed, so audio that is still at film
speed is out of sync with the video. Usu-
ally, you will be working at video speed,
though Digidesign and Avid do provide
several options for film speed (24 FPS) sup-
port.
Pull Up and Pull Down
Pull Up and Pull Down are terms used to re-
fer to the deliberate recalibration of the
audio sample rate clock (speed, or musical
pitch) in order to compensate for a speed
change. Pro Tools can be used to Pull Down
or Pull Up audio for use with NTSC video.
Pro Tools does not support Pull Up or Pull
Down sample rates for PAL video.
Pull Up and Pull Down are based on the
concept of matching the change in audio
speed to the change in video speed. Be-
cause film that has been transferred to
NTSC videotape has been slowed down by
0.1%, the same varispeed (or “pull-down”)
must be applied—at some stage of the
audio production process—to any produc-
tion sound, to maintain sync.
Using Pro Tools in Pull Up or Pull Down
modes requires a USD, SSD, or a third-party
synchronizer that supports 256x clock out-
put and Pull Up and Pull Down sample
rates. The VSD can be used for Pull Down,
but does not support Pull Up mode.
When to Pull Up or Pull Down
There are many ways to get audio into
Pro Tools for post-production. Consider
your source audio and your final destina-
tion format carefully. In some cases, audio
will already be pulled down for you. In
other cases, audio will have to be tempo-
rarily pulled down. In still other cases, you
may choose to pull down your audio
source, like a DAT deck, then use a D-A-D
(digital-to-analog-to-digital) conversion to
record the audio into Pro Tools at the
proper sample rate. Or you may choose
only to pull Pro Tools up or down on deliv-
ery of the audio. Refer to the online docu-
ment FilmSync.pdf installed with your
Pro Tools documentation, for detailed Pull-
Up/Pull-Down workflow information.