User`s guide

Pro Tools Reference Guide332
VITC Speed Usage
VITC’s ability to capture a time code value
when moving a VTR transport at slow
speeds or when the VTR is paused makes it
more useful in audio post-production envi-
ronments than LTC.
When VITC is used, Pro Tools captures the
current SMPTE time from the VTR when it
is paused or in “crawl” mode. However, if
you are using additional external transport
synchronizers in your setup, most synchro-
nizers cannot read VITC at speeds exceed-
ing about 10 times playback speed, pre-
venting slaved machines from maintaining
synchronization during rewind and fast
forward.
LTC/VITC Auto-Switching
Many synchronizers and devices support
automatic switching between LTC and
VITC, depending on the speed, to get the
best of both worlds. For example, VITC
might be used when a VTR is paused, or
crawling frame-by frame, while the syn-
chronizer might automatically switch to
LTC when fast-forwarding.
Bi-Phase/Tach
This electronic pulse stream is used by film
mag recorders, film editing stations, and
film projectors. You can use this format to
synchronize Pro Tools if you have a USD.
Unlike time code, bi-phase/tach doesn’t ac-
tually contain absolute location informa-
tion. It simply supplies speed (based upon
the frequency of the pulses) and direction,
and therefore, relative position. Since the
USD can “count” both the speed and direc-
tion of the stream of pulses, it can use a bi-
phase/tach source to deduce positional in-
formation from a starting “address point.”
The difference between bi-phase and tach
formats is that bi-phase encodes rate and
direction on a pair of signals using a format
called phase-quadrature, while tach en-
codes rate on one signal and direction on
the other.
SMPTE Frame Formats
Six different formats of SMPTE time code
exist, and Pro Tools can sync to any format
with a compatible sync peripheral. The
supported SMPTE frame rates are:
• 30 FPS (frames per second), also called
30 Non-Drop
• 30 FPS Drop frame
• 29.97 FPS, also called 29.97 Non-Drop
• 29.97 FPS Drop frame
• 25 FPS (also called EBU)
• 24 FPS
✽ When you work with NTSC video (the stan-
dard in North America), you will generally work
with the NTSC color video standard: either
29.97 FPS Non-Drop or 29.97 FPS Drop frame.
30 FPS Frame Format
This format is based on a frame rate of 30
frames per second. This is the original
SMPTE format developed for monochrome
(black & white) video, and is commonly
used in audio-only applications. This for-
mat is often referred to as 30 Non-Drop
frame format.