Nevion FSR-HD - Manual (Page 15)

FRS-HD Rev. G
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3.11 Audio de-embedder
The Audio de-embedder extracts all audio embedded in the video stream. The de-
embedder is always enabled.
3.12 Audio delay
An audio delay relative to the video output can be specified commonly for all de-
embedded channels. This is done in GYDA. The audio delay is specified in audio
samples relative to the output video, and can be both positive and negative.
NOTE: As the audio delay is relative to the video output it is possible to specify an audio
delay that will be an actual negative delay. This will cause audio errors.
The negative audio delay is limited by the positive video delay. Since the audio delay is
always relative to the video, the only way to give the audio a negative delay is to delay
the video by a positive amount. To go beyond this limit would require the audio to be re-
embedded before it had even been de-embedded from the incoming video, and that is
of course impossible.
The positive audio 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). When doing these calculations, remember that if a sync reference is
present, a video delay setting of N frames means that the actual video delay can vary
continuously between N and (N+1) frames. The calculations should therefore be based
on (N+1) frames.
3.13 Audio cross point matrix
The audio cross point matrix is a 10x10 cross point with inputs and outputs as shown in
Figure 8. The 8 de-
embedded channels, a 1 kHz sine and “black sound” are selectable
inputs. “Black sound” is explained in Chapter 3.1. The outputs of the cross points are 8
stereo channels for re-embedding, one analog audio output and one AES output.
All outputs have fallback options that can be set in GYDA. The priorities can be selected
between matrix (being the choice in the cross point matrix), sine or black.
3.14 Audio generator
The stereo audio generator is available in the audio cross point matrix as a source. It is
a high purity 1 kHz sine wave with a 250ms interruption on the left channel every 3
seconds. The audio level may be set to one of two standards. The two levels are -18
dBFS and -20 dBFS. These two levels correspond to EBU R68 and SMPTE RP 155.