GUIDE TO INSTALLATION AND OPERATION
14
| FRS-3901
When a reference is present and the deglitcher is active, the card reports the difference in timing between the input
and the reference when the transition occurs.
•
If the reference is missing when the deglitcher is activated, the Input timing to reference box will indicate
“Missing reference” in red, and the reference status icon at the top of the iControl window will turn red and show
the message “Reference missing”.
•
If the deglitcher is OFF, the reference status icon will be grey, and its message will read “Reference absent”
To perform a glitch-free switch between two
sources, they must be in the same clean switch
region. A clean switch region is contained within
± ½ line about an H=0 point in the reference
signal, as shown by the dotted lines in the
figure. There is a clean switch region centered
on every H interval. As you can see, vertical
alignment with the reference is not important for
the deglitcher to operate properly.
Referring to the figure on the right, you may
switch between signals A, B or C, without any
glitch, and also between signals D
E and
signals F
G. Any other transition, like A
D,
will cause a vertical image shift for one frame.
To determine whether a clean hot switch is
possible, you need to determine whether the two
input signals lie in the same clean switch region. There are two ways to measure the position of the signals with
respect to the reference:
•
Use the deglitcher tab in iControl (Input
Deglitcher)
•
Use the controller menu in Annex 1 (video
timing
in timing to ref).
When the deglitcher mode is on, each of these sources will display the alignment offset between the reference signal
and the input signal. Knowing the offset for both input signals, you can determine if they are in the same clean switch
region. If so, any hot-switch between those two signals will be glitchless.
To determine the limits of a clean switch region, you must know the input’s line length in
µ
s. The first region is
delimited by +½ line and -½ line of the reference. For example, with an SD (525) signal the line length is 63.5
µ
s and
so the first region lies between -31.76
µ
s and 31.76
µ
s. Other regions can be found by adding or removing a multiple
of line length to the two boundaries.
Example: for an SD (525) input signal, we have these clean switch regions:
-1 line and -31.76
µ
s to 0 line and -31.76
µ
s
0 line and -31.76
µ
s to 0 line and 31.76
µ
s
0 line and 31.76
µ
s to 1 line and 31.76
µ
s
etc.
Practical examples:
Example 1:
we have two SD (525) sources, one that indicates an offset of -25
µ
s with respect to the reference (A)
and the other an offset of -35
µ
s (B). We know that a clean switch region limit is present at -½ line, which corresponds
to -31.76
µ
s. We can now determine that this switch will not be clean, because the two sources are on opposite sides
of the limit, and are therefore not in the same clean switch region.
Ref signal
Signal A
Signal B
Signal C
Signal D
Signal E
Signal F
Signal G
H=½ line
H=½ line
H = 0
Line = x
H = 0
Line = x+1
clean switch region #2
H = 0
Line = x-1
clean switch region #3
clean switch region #1
H=0
V=1
H=0
V=1
H=0
V=1
H=0
V=1
H=0
V=1
H=0
V=1
H=0
V=1
