Nevion PGM-HD-2x1-PB - Manual (Page 13)

PGM-HD-2x1-PB Rev. B
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until one of the physical inputs is selected again. This is also true when input select is
controlled from the GPI inputs. Two GPI input lines are available and activating one of
them will select the corresponding physical input, while activating both of them at the
same time will force a fade to black. The video will then consist of black frames only
until a single line is activated again. If both lines are released at exactly the same time,
the module continues to output black frames. If
– say – line 1 is released first, while line
2 stays activated, that will be interpreted in the same way as if line 2 was activated
from the released position, and a fade to input 2 will be performed.
Figure 5: Gyda view of input select with additional control blocks.
Note that if a new fade/switch command is issued while the previous one is
still being executed, the first fade will be abrupted and the second one will
be started immediately. This happens regardless of how the command was
given (Multicon or GPI). Continuous toggling of one of the GPI lines will
constantly restart the fade out action and thereby returning the luma gain to
1, and the result will be perceived as flickering in the video luminosity.
5.3 De-glitcher (no settings)
The de-glitcher corrects timing errors within a line. The de-glitcher has a 2048 samples
buffer. When the first signal is present, we call it the “initial phase signal”, data is taken
from the centre of this buffer. If the timing reference of the video signal changes, when
for instance a new source being switched into the signal path, the timing errors
occurring by this change will be corrected if the new timing reference is within +/-1024
samples of the “initial phase signal”. This also goes for all consecutive timing
references.
If a signal is more than +/- 1024 samples off relative to the “initial phase signal”, the
output will repeat the last frame, refill the 2048 samples buffer and take out data from
the centre of the buffer. This new signal is now considered the “initial phase signal”.
Audio will fade out when a frame repeat is being done, and fade in at the new frame.
Hence, it produces an error free video output without frame wrapping when the video
input comes from a router with synchronous input video signals that all lies within +/-
1024 samples of each other.
The de-glitcher output is always seamless. When a signal is repeated the
audio is faded out. It fades in at the new frame.
5.4 Frame synchronizer
The frame synchronizer consists of a frame store buffer and some control logic. The
frame store buffer can store up to 8 full HD frames. Data is fetched from this buffer
according to the user settings by force of the control logic. The control logic sets the
frame synchronizer into different modes dependent on the presence of a sync input.