Nevion DWC-HD-DMUX - Manual (Page 10)

DWC-HD-DMUX Rev. F
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3.2 Video blocks overview
Figure 2: Video function blocks when down-converting HD to SD
3.3 Optical/ Electrical input selection
The DWC-HD-DMUX has both an optical and an electrical input. The active input can be
chosen either by an automatic selection based on a prioritized list of inputs and a selected
rule of switching or by manual selection. When in Gyda over-ride mode (control by DIP
switches), the card will use the priorities and rule saved from the last Gyda session.
Automatic selection mode
Mode under Video in in Gyda must be set to auto. Three input choices can be made for
three priorities; optical, electrical or mute. The priority is the order in which the board will
look for a valid input.
It is also possible to set a rule for when the input should be switched to the next priority.
The rules are:
- lol (loss of lock)
- los (loss of signal)
- EDH (Errors are found in the video frame)
Hold time determines how long a signal has to be missing/unlockable/contain errors to be
considered lost, while Lock time determines how long a higher prioritized signal has to be
present/locked/error free before it again can be considered to be present and stable. This is
described in more detail in chapter 3.6.1, most mainly in t
he two “If video input disappears”
sections.
3.4 De-glitcher
The de-glitcher corrects timing errors within a line of video.
The de-glitcher has a buffer of 13.6 µs for HD and 50 µs for SD. 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, for instance when a new source is being
switched into the signal path, the timing errors occurring by this change will be corrected if
the new timing refer
ence is within ±6.8 µs (for HD, ±25 µs for SD) of the “initial phase
signal”. This also goes for all consecutive timing references.