Specifications

Chapter 34: Synchronization Concepts 543
called phase-quadrature, while Tach encodes
rate on one signal and direction on the other.
For more information on Bi-Phase/Tach, see the
SYNC I/O Guide.
SMPTE Frame Formats
Several different formats of SMPTE time code ex-
ist, and Pro Tools can synchronize to all com-
mon formats with a compatible synchroniza-
tion peripheral.
Pro Tools supports the following SMPTE frame
rates:
30 fps Frame Format
This is the original SMPTE format developed for
monochrome (black & white) video, and is com-
monly used in audio-only applications. This for-
mat is often referred to as 30 Non-Drop frame
format.
30 fps Drop Frame Format
Some field film recordings are done at 30df so
when they get pulled down after the telecine
transfer, they will end up as 29.97df.
29.97 Non-Drop Frame Format
This format is used with NTSC color video. It
runs at a rate of 29.97 fps.
29.97 Drop Frame Format
NTSC color video has an actual frame rate of
29.97 fps, so an hour’s worth of frames
(108,000) running at 29.97 fps Non-Drop will
take slightly longer than one hour of real time
to play. This makes calculating the actual length
of a program difficult when using 29.97 Non-
Drop time code. A program that spans one hour
of 29.97 Non-Drop time code addresses (for ex-
ample, from 1:00:00:00 to 2:00:00:00) is actually
60 minutes, 3 seconds and 18 frames long.
To make working with 29.97 time code easier for
broadcasters, the SMPTE committee created
29.97 Drop Frame time code, which runs at ex-
actly the same speed as 29.97 Non-Drop (non-
drop frame) time code, but compensates for the
slower speed by “dropping” (omitting) two
frames at the top of each minute, with the ex-
ception of every 10th minute. For example, the
time code address of 1:01:00:00 does not exist in
drop frame code because it has been skipped.
At the end of a program that spans precisely one
hour of drop frame time code (for example,
1:00:00;00 to 2:00:00;00), exactly one hour of
real time has elapsed.
Although it sounds complicated, drop frame
time code allows broadcasters to rely on time
code values when calculating the true length of
programs, facilitating accurate program sched-
uling.
When you work with NTSC video (the stan-
dard in North America and Japan), you will
generally work with the NTSC color video
standard: either 29.97 fps Non-Drop or
29.97 fps Drop frame. If you are working
with PAL, your frame rate is 25 fps.
Note that even though time code addresses
are skipped in drop frame format, actual
frames of video material are not dropped.