Nevion DWC-HD-DMUX - Manual (Page 16)

DWC-HD-DMUX Rev. F
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3.12 Audio overview
Figure 4: Audio function block
3.13 Audio de-embedder
The Audio de-embedder extracts all audio embedded in the video stream. The de-
embedder is always enabled when the input is HD. When the input is SD and the board
operates as an SD frame synchronizer, embedding can be globally disabled. The effect is
to leave the SDI stream unaltered, except for repeated or removed video frames.
3.14 Audio delay
An audio delay can be specified relative to the video output. It is situated before the audio
cross point matrix and is common for all de-embedded channels. The audio delay is
specified in terms of 48 kHz audio samples, and can be set to positive or negative values.
NOTE: As the audio delay is relative to the video output it is possible to specify an audio
delay that will actually be a negative delay, i.e. ask that the sound is sent from the card
before it is received. This will obviously cause audio errors.
3.15 Audio cross point matrix
The audio cross point matrix is a 10x10 cross point with inputs and outputs as shown in
Figure 4. 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.
3.16 Audio fallback options
The 10 output channels from the cross point matrix have configurable fallbacks, used when
their corresponding matrix inputs are missing. A common fallback setting is used for all
eight re-embedder channels, whereas the audio DAC channel and AES out have their own
independent fallback settings. The priorities can be selected between matrix (being the
selected channel in the cross point matrix) or the internally generated sine or black sound.
3.17 Audio generator
The stereo audio generator is available as an input to the audio cross point matrix, and as a
fallback option. There are therefore three slightly different ways to select the generator:
select it in the matrix directly, select it as the first priority under audio fallback, or to set it as
second priority behind a missing input.
The generator signal 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
RP155.