MTX SW2 User Manual download pdf (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.

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MTX SW2 User Manual Page 9