Nevion AES-VMUX - Manual (Page 9)

Introduction 9
AES-VMUX/-SFP User Manual Rev. G
• PIN/Standard laser tranceiver
The following Nevion video SFPs may be used but only one of the channels will be utilised.
• PIN dual receiver
• APD dual receiver
• Standard short haul dual laser
• CWDM dual laser
The optical input provides an extra input and the actual input may be chosen automatically or
set manually to the required input. In “Auto” mode, the input switches if a suitable signal is not
present, or if the signal disappears. There is no priority, the first input with a valid Nevion SDTI
audio signal is used.
4.1 The Nevion SDTI audio concept
The Nevion SDTI audio uses a normal 625 video frame and data format. This allows simple reuse
of existing legacy infrastructure and standard test and signal monitoring facilities.
The audio is embedded into the active video area on all video lines. An extra ancillary data packet
in the horizontal blanking area identifies the signal as a Flashlink SDTI audio multiplex.
The audio embedding uses two video lines to optimize the number of channels in the multiplex.
Seven stereo audio samples, embedded over two lines gives a maximum sample rate of 54.7 kHz.
This gives a high multiplexing efficiency of normal 48 kHz broadcast audio. The embedding pat-
tern repeats over a two frame sequence. The phase reference is only inserted on one of the the two
lines and a frame counter is also embedded into the horizontal ancillary data packet.
The audio is embedded in fixed timeslots placed along the video line. The phase words are embed-
ded in a block of video words placed first on every other line followed by seven audio blocks. Each
audio block has 64 audio timeslots. Each timeslot contains a 24 bit audio sample together with the
C, U and V bits from the AES subframe. The frame of AES audio is split between two audio blocks.
The audio multiplex appears on a video monitor as a series of vertical lines or stripes on a video
monitor. Dark green stripes are areas where no audio is embedded. Light green shows that the
channels are embedded but that the AES input is absent. An active audio channel appears as a
multicolored vertical stripe.
The SDI embedded clock is used as a clock reference and the audio is sampled with reference to
the start of the horizontal blanking. The phase measurement (similar to HD audio) is embedded
on the following line. All of the audio channels use the same reference point and all of the phase
measurements are embedded together in a block.