The Changing Face of Audio Routing

LOS ANGELES: A presentation at the DTV Audio Group meeting during the recent New York AES Convention highlighted an operational difference between many European and U.S. broadcast audio infrastructures, particularly in remote trucks: the use of the console router instead of a patchbay. Although large-scale analog audio patchbays would seem to be redundant in today's increasingly all-digital static and mobile plants, there appear to be various barriers to a more widespread adoption of the onboard software router available in digital broadcast consoles.


In many European OB vehicles, console software routers are used instead of the large hardware patchbays more common in the U.S., such as this example in NE P's Denali Summit truck, with audio engineer Hugh Healy. Photo by The Recording Academy/ ©2011. Photograph by John Shearer Switching from racks of metal patchbays and associated copper wiring in a truck to a GUI-driven in-console router would offer major weight and cost savings, of course. But in the opinion of Steve Zaretsky, vice president, broadcast sales, Solid State Logic, a patchbay allows easy reconfiguration in situations where there are multiple users or applications. Plus, in emergencies, "If you have to get around an issue, if you don't have a patchbay, you're a lot more limited in what your emergency plans can be."

That said, there has certainly been a move by broadcasters toward the use of MADI—an AES standard—as a distribution method, reducing the use of copper significantly. "Even if you're doing a lot of patching, the interconnectivity has been really cut down by implementing MADI," Zaretsky said.

Zaretsky further noted, "In the studio environment we've seen more of our customers starting to utilize the console's audio routing facilities for communications, de-embedded audio and control signals, all within the MADI architecture. As one of the founders of the MADI spec we're very happy to see broadcasters recognize that the low latency point-to-point routing offered by MADI is still an advantage over newer network based protocols."

Although MADI, a 25-year-old format that carries up to 64 channels, initially disappeared from recording studios along with Sony DASH machines, the broadcast industry has embraced it over the last five or more years. According to Dave Letson, regional director of sales at U.K.-based Calrec, "Pretty much every truck that we're involved with now has several MADI boxes, and each of our boxes has at least two connections." Some consoles use multiple MADI connectors to interface with the router, comms, recorders, and other trucks, he added.

But Mike Franklin, senior sales manager for Studer, noted that there are stumbling blocks to the adoption of a console's onboard routing facilities, including the implementation of the GUI and the protocol for patching a source through a DSP channel to an output. "Ten console manufacturers have 10 ways of doing it," he said, noting that Studer's multi-touch screen offers a streamlined solution. "How well it gets managed on that patch screen is the difference in ease of use between consoles."


Letson additionally noted a move toward SDI. "You put an SDI input on a console and you feed that with the SDI stream and pull off the channels that you want. That can be done via the router—and it's still the video router; you do not have to have a separate audio layer." At the same time, said Letson, Calrec is receiving more requests for the console to be controlled by the router with a third party control system.

This was echoed by Zaretsky who also noted the increased demand for more studio-integrated solutions on both sides of the Atlantic.

There's a challenge there, too, according to Franklin: "The protocol that's used for switching within routers is old." That protocol, Pro-Bel's SW-P-02 and SW-P-08, doesn't allow for certain switching within combined streams, he said. "You can use translators but there are issues with how things work." The industry can expect protocol updates over the next year or so, he believes.

Many console manufacturers' distribution and routing systems are essentially I/O systems, according to Rusty Waite, president, Stagetec USA in Atlanta. In contrast, Stagetec—as well as fellow German manufacturer Lawo—takes a different approach. "We're a router company that has built consoles onto a router rather than a console company that's trying to build a router," he noted. That experience has allowed the company to overcome challenges such as timing, clocking, sync, stability, and implementing different flavors of I/O cards, he said.

Most importantly, stressed Waite, Stagetec's Nexus router, which can break out to numerous protocols and connectors, offers decentralized control, unlike a console's router. Depending upon the permissions set for the system, anyone can have access from any point on the network to route any signal anywhere without having to bother the A1. For example, Waite said, a single network-connected Nexus base device can access ESPN's entire 20,000 x 20,000-point router setups in Bristol or L.A.

On a smaller scale, Logitek, to take one example, manufactures TV broadcast consoles following a similar paradigm to Stagetec, where the console is simply an operating surface on a router system. The core Audio Engine can replace part or all—as many as 32 engines may be combined—of the house router, as a result. Engines may be physically separated according to fiber specifications: up to 600 feet apart using multimode, 10 km with single mode.

But while there's no reason for U.S. broadcasters to not already be using MADI, Waite continued, "MADI is not the future; the real future is AVB [Audio-Video Bridging]." The IEEE-developed future A/V transport standard is backed by major corporations such as Cisco and Broadcom: "They're going to push it forward and we're going to be able to piggyback on there."

One significant advantage is that AVB utilizes Cat 5 cable, noted Waite. "You could clip a Cat 5 and leave it behind. Try telling that to someone who's laid a DT12 cable!"

Steve Harvey began writing for Pro Sound News and Surround Professional in 2000 and is currently senior content producer for Mix and a contributor to TV Tech. He has worked in the pro audio industry—as a touring musician, in live production, installed sound, and equipment sales and marketing—since November 1980.