Model 5601MSC
Model 5601MSC Master SPG/Master Clock System
Page - 46
Revision 2.2
OPERATION
2.3.4.2. LTC/VITC Timecode Color Framing
If the Color Frame control is turned on, the 25Hz and 29.97Hz LTC timecode rates will have their
counts adjusted by the 5601MSC so that they maintain color frame alignment to the selected frequency
reference as per SMPTE ST 12-1. If a black burst sync output has its Color Frame control turned on,
the VITC timecode is adjusted to same way to maintain color frame alignment to that particular black
burst sync output. See the pulse diagrams in Figure 2-4 and Figure 2-5 for examples of timecode color
frame alignment.
2.3.4.2.1.
Color Frame Alignment to NTSC
Color frame alignment can be enabled for any NTSC sync output and for LTC timecode that runs at
29.97 frames per second. Even frame counts must coincide with color fields 1 and 2. Odd frame counts
must coincide with color fields 3 and 4. When a system time jam event occurs, the timecode output
clock is jammed to system time and then adjusted, if necessary, to match the color frame phase of the
particular LTC or sync output.
The consequence of color frame alignment is that the LTC/VITC timecode may be jammed one frame
count off of real-time, depending on the phase of the frequency reference and the phase of the LTC or
sync output. See Figure 2-18 for an example of daily time jamming involving dropframe timecode.
2.3.4.2.2.
Multiple LTC/VITC Outputs with Dropframe Counting
It should be evident that dropframe timecode maintains only a loose correlation to real-time, and cannot
always be jammed exactly to real-time. Dropframe timecode counts an entire 24-hour period 86.4
milliseconds faster than real-time. This is the equivalent of 2.59 frames of video. At the daily jam event,
when the timecode clock is jammed to the system clock, some extra frame counts will have to be
inserted to bring the timecode closer to real-time. It is not possible to adjust by fractional frame counts.
Either 2 or 3 frame counts must be added, which means the timecode output cannot be jammed exactly
to the system clock and some error will occur. If color frame alignment is enabled, the extra frame
counts can only be inserted in pairs. Therefore, 2 or 4 frame counts will be inserted, depending on the
error accumulated from the previous daily jam.
See Figure 2-18 for an example of a daily
jam
event for LTC1 in 29.97Hz dropframe counting mode.
When the timecode of LTC1 hits the daily jam time, a
jam
to the real-time
system clock
is performed.
However, the number of extra counts inserted is adjusted to maintain color frame alignment to the
frequency reference (either GPS or NTSC). If the timecode output was VITC, the adjustment would also
have to factor in any phase offset that may have been applied to the respective sync output.
Figure 2-18: Daily Time Jam Event for 29.97Hz Dropframe Timecode
NTSC-M
REFERENCE
LTC1
System Clock
Color Frame A
LTC1 DAILY JAM
EVENT AT 00:00
LTC1 timecode count reaches 00:00:00:00.
UTC hh:mm:ss.ms
23:59:59:27
23:59:59.814
23:59:59.847
23:59:59.880
23:59:59.914
23:59:59.947
23:59:59.980
00:00:00.014
00:00:00.047
Color Frame B
Color Frame A
Color Frame B
Color Frame A
Color Frame B
Color Frame A
Color Frame B
23:59:59:28
23:59:59:29
23:59:59:28
23:59:59:29
00:00:00:00
00:00:00:01
00:00:00:02
Should jam 23:59:59:27 but is adjusted to
23:59:59:28 to maintain color frame alignment
Содержание 5601MSC
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