The Score Magazine - Archive August 2015 issue! | Page 38

NETWORKED AUDIO
AND RAVENNA
Ravenna is a technology for real-time transport of audio and other media data
in IP-based network environments. RAVENNA, when referenced to real-time
audio, is just like MADI, AES-EBU, ADAT or other digital audio "streams", it is used
to send and receive audio between digital devices. But, RAVENNA has one, very
large difference. RAVENNA, rather than forcing static interconnections between
devices, allows the user instead to use a standard, off-the shelf, network switch
to become a type of 'hub' which allows all the RAVENNA devices to talk to one
another. This RAVENNA network then allows for the transport of hundreds of
channels of real-time audio, at incredibly low latencies, to be sent to and from
any of the devices on the network.
Practical Benefits of Networked Audio
With the introduction of digital technologies the amount of
information a single cable can carry has increased from a few
thousand bits per second in the sixties to a few billion bits per
second in 2014. Typical methods of transmitting digital audio data
are inefficient, expensive and prone to failure. Transmitting signals
using AES3 or AES10 require large quantities of expensive copper or
fibre cables with a variety of connectors. These solutions only handle
point to point connections and offer very limited opportunities to
transmit additional data down the line. There are limitations to the
length of cable runs and signals need complex and bulky routing
solutions to offer similar functionality to an analog patch bay.
Using a standard IT network allows the use of inexpensive routing
and cabling and drastically reduces the number of cables in the
installation. Regular affordable connections in every day information
systems now carry one or more gigabits of information in a single
fibre cable over distances spanning many kilometres. By its nature,
Ethernet is bi-directional so a single cable can carry hundreds
of audio channels in either direction and signals can be multicast
to any device on the network. IP networks address issues such as
redundancy and transmission of control information with audio and
video signals. The ability to be able to control signal distribution
using simple web browsers opens up a myriad of possibilities and
removes stand-alone expensive routers. More importantly, the
functional connections in a networked audio system can be designed
separately from the physical connections in the network. All current
computers feature a GB Ethernet port providing easy connection and
control of the standard RAVENNA network.
A networked audio system is digital so audio connections are kept
in the digital domain, far away from electromagnetic interferences
and cable capacitances that degrade analog audio quality. Control
signals can also be included in the network without additional
cabling. Computers can use the network to control and monitor
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audio devices such as digital mixers and DSP engines.
While on the surface AoE bears a resemblance to Voice over IP
(VoIP), AoE is intended for high-fidelity, low-latency professional
audio. Because of the fidelity and latency constraints, audio over
Ethernet systems generally do not utilize audio data compression.
AoE systems use a much higher bit rate (typically 1 Mbit per channel)
and much lower latency (typically less than 10 milliseconds) than
VoIP. Audio over Ethernet requires a high-performance network.
RAVENNA Technology Background and
Applications
Networked audio has been in use for some years with Cobranet
and Optocore being introduced in 1996. In the last decade, several
proprietary network protocols were introduced for broadcast and
live usage. An element of standardisation began with the adoption
of IEEE-1588-2002 synchronisation which was adopted by Audinate
and QSC. However, these protocols remained proprietary and
incompatible. ALC NetworX introduced an open IP networked audio
protocol in 2010 which took advantage of the latest IEEE-1588-2008
amendments and concentrated on offering essential features for
high quality audio transmission over standard IT infrastructure.
Particular notice was paid to delivering low latency and QOS (Quality
of Service) that would be compatible with the needs of broadcasters.
The growing family of RAVENNA partners reflects this emphasis
on broadcast as a primary target but RAVENNA has applications in
all market sectors where these features are a must. The publication
of the AES67 standard in 2013 established that RAVENNA was
already AES67 compliant but was able to offer additional benefits
beyond the scope of that standard. The news that creators of other
network protocols have announced that they are either joining the
RAVENNA group or becoming AES67 compliant means that there is a
genuine opportunity to see the widespread adoption of interoperable
networked audio in facilities throughout the globe.