Cc Level Setup Menu - Ultech Corporation DV2000 User Manual

22 ULTECH DV2000 User's Manual

4.7 CC Level Setup Menu

DV2000 allows you to adjust the "data bit low" level and "data bit high" level of the en-
coded closed caption waveform. Normally, the adjustment is made such that data bit low
produces a 0 IRE level, and data bit high produces a 50 IRE level. In an analog encoder,
these adjustments are usually
made with a trim pot. In the
DV2000 digital encoder, the
adjustments are made by
specifying a numeric value,
either from the front panel or
via a script command.
SMPTE 125M specifies the assignment of luminance values as 877 quantization levels with black
level corresponding to level 64 and the peak white level corresponding to level 940.
sponds to 100 IRE. This is usually termed "no 7.5 IRE setup" or "without setup". The second
solution is to use the values 1-15 to generate the IRE values below the value of 16 (7.5 IRE).
An IRE value of zero is not possible because zero is reserved for TRS indication. This is
usually termed "with 7.5 IRE setup" or "with setup".
The existence of both solutions in the field complicates the task of inserting VBI waveforms
into D1 video. The DV2000 solves this problem by allowing the user to set the min and max
values used to generate closed captioning waveforms.
D1 value
8 bit IRE with IRE without
setup setup
1 1.16 -
2 1.59 -
3 2.01 -
15 7.08 -
16 7.50 0.00
17 7.92 0.46
116 49.74 45.66
117 50.16 46.12
118 50.58 46.58
125 53.54 49.77
126 53.96 50.22
127 54.38 50.68
235 100.00 100.00
Reserved to indicate TRS
Black Level
White Level
Reserved to indicate TRS
* The DV2000 waveform generator uses 8 bit values
The spec fails to address the levels used by VBI
services such as Closed Captioning and NABTS
teletext which are referenced to blanking level (0
IRE). So the industry has responded with two
solutions. The first solution is to change the slope
of the DAC during the VBI so that the value of 16
corresponds to 0 IRE and the value of 235 corre-
ï nominal min with setup
ï nominal min w/o setup
ï nominal max with setup
ï nominal max w/o setup
Data Bit High
Data Bit Low
IRE 10 bit
- 0 (000H)
7.5 64 (040H)
100 940 (3ACH) 235 (EBH)
- 1023 (3FFH) 255 (FFH)
Table 4.1 IRE vs. D1 Level
8 bit *
0 (00H)
16 (10H)