Appendix 1

Pull Down when Shooting Film
Initial Audio Workfl ow, Importing Production Audio, and Syncing
Pull down is an issue when shooting fi lm at 24 FPS and fi nishing or editing on video. In telecine,
the fi lm will be slowed by .1 percent and, so, the audio recording must be matched to this new speed.
Slowing the fi lm to 23.98 FPS to produce 29.97 FPS video will cause the sound to slowly move out
of sync. It will be one full frame out of sync after 33 seconds. When syncing up fi lm either in telecine
or after it has been telecined, it is necessary to also slow the audio by the same .1 percent. For more
information, see Chapter 1 on telecine and pull-down.
Here again, fi lm speed will refer to any fi lm or digital video or audio that plays at 24 FPS or 30 FPS.
Video speed will refer to fi lm, video, or digital that plays at 29.97 FPS or 23.98 FPS. If you are
changing from fi lm speed to video speed, you are pulling down. If you are changing from video
speed to fi lm speed you are pulling up.
Some digital recorders have pull-up and sometimes pull-down sample rates. In this case, the recorder
would be set for pull up (48,048 Hz or 96,096 Hz) while fi lming and normal (48 K or 96 K) for
transferring to Pro Tools or tape. It would also be played at 48 K or 96 K if syncing in telecine.
Some recorders have this pull-up, pull-down feature but don’t call it pull up or down. Often, this is
expressed as 30 FPS and 29.97 FPS. Audio recorders don’t actually record frames, but this is a convenient
way to express the speed. Here, too, if the recording is done at 30 FPS and playback is set
to 29.97 FPS, the audio has been pulled down.
Many of these recorders also lay time code from a free-running time code generator or a time-of-day
time code generator. These can usually generate several different time code formats, both drop frame
(DF) and nondrop frame (NDF) in 23.98, 24, 29.97 and 30 FPS. (For more information on time code,
see Appendix 5 on understanding time code.) If the production time code is 24 or 30 FPS, the pulled
down audio will be 23.98 and 29.97, respectively. This is why some production recorders offer 30
and 24 DF, which are not real or rational time code formats. These time codes become 29.97 DF and
23.98 DF, which are real time code formats.
Hard Lock Versus Soft Lock
There are many ways to lock sound and picture together for sync, but they can be divided into two
types: soft lock and hard lock. There was a time when only hard lock was used in motion picture
production and postproduction. But, thirty years ago, when new, more accurate technologies became
available, soft lock systems came into common usage.
In a hard lock system the elements are locked together so that they must move at the same speed.
Original systems often used mechanical systems, gears and chains with common motors. There were
also electrical systems that used selsyn motors to lock separate machines together. Often the camera
and audio recorder would be locked to a common speed reference.
Later, pilot tone systems came into usage. Figure 3.2 shows an early system. The camera sent a pilot
signal to the audio recorder that could then record the speed of the camera with the audio. This was
used to hard lock all audio recorders and players to the speed of the camera. All of these systems
are examples of hard lock where the separate devices are either locked together or are locked to a
common speed reference.
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