User`s guide

Chapter 23: Synchronization Concepts 331
does offer powerful features for post-pro-
duction professionals who work with
video.
There is also a non-SMPTE form of time
code called MIDI Time Code (MTC) that
some devices use to send timing informa-
tion.
Time code is timing information in the
form of a data stream that can be recorded
on magnetic tape as an audio or video sig-
nal. Time code can be used to synchronize
the playback and recording of your
Pro Tools system with another machine’s
transport, such as an analog multitrack
tape machine or a video tape recorder
(VTR).
Time code is based on hours, minutes, sec-
onds, frames, and subframes (1/100th of a
frame). The frame is used as a unit of time
measurement due to SMPTE time code’s or-
igin in film and video applications. De-
pending on the SMPTE frame rate, one
frame is equal to 1/24th, 1/25th, 1/29.97th,
or 1/30th of a second. For instance, a vid-
eotape time code reading of “01:12:27:15”
would tell us that we were at a position of
one hour, twelve minutes, twenty-seven
seconds, and fifteen frames.
Because SMPTE stores an absolute time ref-
erence on the tape in the form of time
code, any location on that tape can be pre-
cisely located by devices that read time
code. Once the time code has been re-
corded or “striped” on a tape, it provides a
permanent time reference that allows
Pro Tools to link the playback of an event
to an exact tape location. For example,
with time code sync, a gun shot sound ef-
fect can be played at the precise instant
that the gun’s flash appears on-screen.
LTC (Linear Time Code)
LTC is time code that is recorded and
played back in the form of an analog audio
signal. LTC is supported by many audio
and video tape recorders.
LTC Speed Usage
LTC can be read at high tape shuttle
speeds, allowing a machine’s time code
reader to communicate with synchronizers
at rewind or fast forward speeds exceeding
50 times playback speed (provided the tape
recorder is able to reproduce the time code
at this speed). However, LTC cannot be
read at very slow shuttle speeds (such as
when you are “crawling” the tape frame by
frame) or when the machine is paused.
With LTC, the VTR must be running (usu-
ally at a minimum speed of about 1/10th
normal playback speed) in order to capture
a SMPTE time address.
VITC (Vertical Interval Time
Code)
VITC is a type of time code that’s recorded
and played as an invisible part of a video
signal. VITC is commonly used in profes-
sional video editing and audio-for-picture
applications. Because VITC is recorded as
part of each video frame, it must be re-
corded at the same time as the video sig-
nal—it cannot be added later as LTC can.
Since VITC cannot be recorded on audio
tracks, it is never used to synchronize
audio-only recorders. As a result, LTC is
more commonly used in audio-only appli-
cations.