DISTRIBUTE
Traditionally, we push audio to a distant load through a transmission
line. Signals on a network do not need to be distributed as they were
in the past. With AES67 and SMPTE ST2110-30, you are subscribing to
the stream and the network’s flow control, the IGMP, handles the join
connections for you. The classic audio distribution amplifier is over
50 years old, with a single input and eight outputs or one transmitter
to eight fixed receivers.
With AES67/SMPTE ST2110-30, you have one transmitter and (n)
receivers. The need to distribute signals is no longer required as they
are available anywhere and everywhere at the same time. AES67
signals are discovered using a mechanism like Ravenna (MDNS –
Bonjour), Session Announcement Protocol (SAP – Dante Controller),
and Session Initiation Protocol (SIP). These discovery mechanisms are
a byproduct of the telecommunications industry.
Figure 3: Connection Management with Aneman: A Network
Manager by Merging Technologies
Figure 4: ST Fibre Optic Cables
WORD CLOCK
Word clock is an imperfect one-way communication system for syn-
chronization. Because of its unidirectional transmission, a receiver of
word clock cannot know how far off it is from the generator. Word
clock is a one-way conversation with no start, no finish, and there-
fore no linear reference.
With AES67 and ST2110-30, audio is synchronized using a preci-
sion time protocol (PTP) designed by the IEEE(1588). PTP is a conver-
sation between a master clock server and client edge device. Algo-
rithms are used for elections of the best master clock; this keeps the
network in sync and always with a clock. A PTP master clock can be
generated by an oscillator locally or slaved. There is no clock source
on earth quite like the one not on the earth. Using GPS synchroni-
zation, (n) number of stations/remotes or devices can be perfectly
synchronized and sync-locked continents apart. SMPTE 2059 and
PTPV2.1 are the new timepieces for your audio and video networks.
What good is word clock when you can be world clocked?
Figure 5: IEEE 1588 PTP Clock Conversation
CLIENT
SERVER
When the front of house mixing console 100-plus ft. away from the
stage is receiving microphone signals, it is very susceptible to noise.
If the ground at the console has a different potential to ground than
that of the stage, you’re in trouble. Ditto in a TV studio, radio studio,
recording studio, mobile truck, etc.
With AES67 and networking technologies, there is no need for
a common system ground. It would have no benefit as your sound
is digitally encoded, meaning it is simply packetized data. The sound
is not susceptible to external environmental interference within the
transmission path. You cannot bond fibre optic glass to earth and
optical pulses are not susceptible to electromagnetic interference.
What’s more, ethernet cables are transformer-isolated from the elec-
trical system on which they operate. Power over ethernet derives its
own reference relative to the switch that generates it. Everything is
floating relative to everything else!
Sync Follow
Up Message
Delay Request
Message
SYSTEM GROUND
Sync
Message
Delay
Response
Message
PROFESSIONAL SOUND 39