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Calrec takes broadcast down AVB AVnu

Kevin Hilton 3 April 2013
Calrec takes broadcast down AVB AVnu

Networking has been a major part of audio for broadcast over the last 20 years, as engineers and operators look for greater interconnection and integrated working between different pieces of equipment. Many network technologies – both in the early days of the technology and today – have been proprietary, although the demand for greater communication between systems did bring about increased openness by manufacturers signing up as partners to the original developers of network protocols. But now AVB (audio/video bridging) is emerging as a possible universal solution to the problem of connecting equipment – both audio and video – in a wide area installation. AVB was developed by the IEEE (Institute of Electrical and Electronics Engineers) 802.1 Working Group as a more reliable version of Ethernet that could be used for professional interconnection, networking and data centre bridging. The result is a technology that is able to carry, route and switch audio and video signals over standardised connections using specially designed switches tested and approved under the control of industry forum the AVnu Alliance. Ethernet is used in a wide range of industries and business, so AVB has applications in IT and the automotive sectors as well as professional audio. On the sound side live touring and installation markets were seen as the obvious users of AVB, with Harman, Avid, Shure and Sennheiser among the initial audio members of the AVnu Alliance. Harman and Riedel straddle both live sound and broadcasting but the announcement in March that Calrec Audio was joining the AVnu Alliance put the focus squarely on the possibilities for AVB in broadcast. Calrec’s technical director, Patrick Warrington, agrees there has been "a large number of networking products" in the last decade but the problem was their proprietorial status. "Things like Cobra Sound, and even our own Hydra and Hydra 2, were all great in their own right but they were proprietary," he says. "The reason why AVB is different and why Calrec is excited about it is it is attempting to be a truly open standard that anybody who has an interest can get around and which will address broadcast requirements." Warrington explains that AVB is compelling for broadcasters because it is more reliable, deterministic and predictable than other Ethernet and IP-based systems: "Audio networking technologies have been based on Ethernet because it is a very cheap infrastructure and broadcasters can’t resist using it because of that. But it’s not well suited because of the way it packetises the audio. The audio can get stuck in Etherframes and a series of switches, which is where the unreliability comes in. Data networks can use protocols like TCP/IP, which will re-transmit any packets that don’t get through, but in audio you need the information to get there first time." The IEEE has developed four extensions to the Ethernet format to deal with such problems, making it a more specific pro audio system. Among these is the ability to instruct switches to use a different forwarding mechanism. "That can be very helpful when it comes to streaming," Warrington comments. "This is why AVB differs from anything that went before and other systems that are being developed at the same time." The appeal of AVB, Warrington says, is that a manufacturer like Calrec can design an interface based on the format and then be able to manage connection to and from third party equipment. "AVB allows us to connect to other networks so we see it as a powerful complement to connecting different products, systems and technology," he explains. This capability will be on show during NAB when Calrec will connect two or three consoles on a Hydra 2 network to a Riedel Artist intercom through a new AVB interface. AVB can theoretically handle up to 420 signals but right now the new Calrec interface will link to 64-channels. Warrington picks up on a common misconception that AVB is an Audio over IP (AoIP) system, pointing out it is "Layer 2 audio over Ethernet". He says the distinction is important: "Ravenna and LiveWire are genuine AoIP systems and they have different characteristics to Ethernet and AVB. I won’t argue that one is better than the other, they’re just different." All AVB equipment has to be tested and then endorsed by the AVnu Alliance before it can go on the market. The new interface has not yet been through the compliance tests but Warrington expects that to happen soon and for a "more powerful" Calrec interfacing system to appear in less than a year. www.avnu.orgwww.calrec.com 

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