Nevion SPG-AVA-DMUX - Manual (Page 15)

SPG-AVA-DMUX Rev. C
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3.2.4 Subcarrier delay
Figure 7: Multicon Gyda view of the Subcarrier delay setting
The Subcarrier delay setting will add entire frames to the delay through the module. The
range is 0-7 frames. For strictly periodic signals like Black burst and Tri-level, the delay is not
important as such. There are however two good reasons to care about this delay:
1. A subcarrier delay of at least one frame must be added in order to use negative
phase delays. (The exact same phase between input and output can be achieved by
using a positive phase delay instead, it is just a matter of how one likes to think
about it).
2. The subcarrier of the analog video sync outputs has eight different phases,
i.e. it takes eight frames to complete a full cycle. Most modern equipment, like digital
frame synchronizers, doesn’t need or use the subcarrier phase, but many video
DACs do. Matched subcarrier phases will be necessary to do seamless analog
switching between.
3.2.5 Linear time code
The linear time code (LTC) is de-embedded from the video input. When video delay/phase is
changed by adjusting the Phase delay and Subcarrier delay above, the LTC will automatically
be delayed the same amount as the video. It is possible to add an extra delay to the LTC,
relative to the video outputs. This delay can then be either positive or negative, given as a
number of 48 Hz audio samples. But once again, the negative LTC delay can not be larger
than the total positive video delay. Demanding otherwise would require the LTC to be
presented on the output before it had even been received in the incoming video.
Figure 8: Multicon Gyda view of the Linear Time Code delay setting
While the maximum negative relative LTC delay will be limited by the actual positive video
delay, the maximum positive LTC delay is limited by the fact that the sum of the video delay
and the relative audio delay cannot be larger than 32000 audio samples (approx. 0.67 ms
with 48 kHz audio). If the video delay is set to minimum, the full 32000 audio samples will be
available, but if the video delay is set to
– say – 5 frames, the maximum relative audio delay
is reduced to 20000 audio samples (assuming 25 frames per second, 5 frames equals 0.2
seconds, which in turn equals 12000 audio samples, and 32000-12000=20000).
The LTC is de-embedded from channel 1 and 2 in group 1. The two channels now used are:
channel one for Left and channel two for Right. The default setting is set to LR, this has been
changed from LL when there was only one channel.
3.2.6 Video input
The SPG-AVA-DMUX has one electrical and one (optional) optical input. The input can be
chosen either by an automatic selection with priorities and a selected rule for switching, or by
direct manual selection. When the input selection is done manually by selecting one of the
inputs from the Mode menu, no fallback is available to other sources. Instead there will be a
frame freeze for as long as the input is gone.
If the Video in Mode choice is set to auto in Multicon GYDA, three input choices (priorities)
can be made. The available choices are electrical, optical, internal generator, muted, or
‘–‘
(none). When the signal is missing on the input selected as ‘Main’, the change-over logic will