Audio Engineering

Video Synchronization 839

27 Unassigned

28–31 Fourth binary group

32–35 Minutes units

36–39 Fifth binary group

40–42 Minutes tens

43 Unassigned

44–47 Sixth binary group

48–51 Hours units

52–55 Seventh binary group

56–57 Hours tens

58–59 Unassigned

60–63 Eighth binary group

64–79 Synchronizing sequence

28.10.2 Vertical Interval Time Code (VITC)

LTC is a quasi-audio signal recorded on an audio track (or hidden audio track dedicated
to time code). VITC, however, encodes the same information within the vertical interval
portion of the video signal in a manner similar to a Teletext signal. Each has advantages
and disadvantages; LTC is unable to be read while the player/ recorder is in pause,
while VITC cannot be read while the machine is in fast forward or rewind modes. It
is advantageous that a videotape has both forms of time code recorded. VITC is also
illustrated in Figure 28.16. Note how time code is displayed “ burned in ” on the monitor.

28.10.3 PAL and NTSC

Naturally, time code varies according to the television system used, and for NTSC
(SMPTE) there are two versions of time code in use to accommodate the slight difference
between the nominal frame rate of 30 frames per second and the actual frame rate of
NTSC of 29.97 frames per second. While every frame is numbered and no frames are
ever actually dropped, the two versions are referred to as “ drop ” - and “ nondrop ” -frame
time code. Nondrop-frame time code will have every number for every second present,
but will drift out of relationship with clock time by 3.6 seconds every hour. Drop-frame
time code drops numbers from the numbering system in a predetermined sequence,