Networked digital audio systems may soon be serving a live venue near you
While Routing Digital Audio through networks in audio facilities is nothing new, the past decade has seen developments in the implementation of protocols that may profoundly influence sound diffusion and control at live events. Companies such as Gibson, Peak Audio, QSC, Rane, and Yamaha are but a few of the key players in this sector. Whether they use CAT-5 Ethernet, fiber optic, or FireWire runs, there is a desire to simplify and enhance signal routing, as well as to define a single standard that the industry can adopt over time.
While the latter goal isn't a likely prospect any time soon, migration from strictly analog to streamlined digital audio pathways via these protocols has made an impact on the install sector that will likely affect the live-event industry in the coming years.
The arguments for shifting to digital pathways are commonplace by now. Conduit costs are reduced since multiple channels of audio can be handled via a single cable — you have the ability to send both audio and control information along the same cable, and your noise floor can improve, as well. Plus, the advent over the years of digital routers, remote-controllable amplification systems, live digital consoles, plus the ease with which signals can be sent to multiple destinations without splitters, have combined to set the stage for the looming transition.
A serpentine protocol
Facilities have been anticipating this change for a while. Some invested early in CAT-5 Ethernet wiring infrastructure as a means to handle the eventual demand for networked control in venues. Companies like Peak Audio took advantage of wiring infrastructures that were in place when they developed CobraNet, one of the more popular technologies that several pro audio companies started licensing fairly early in the game. CobraNet delivers audio and data via standard Ethernet packets over 100Mb Fast Ethernet (or over fiber optic), but due to bandwidth limitations it doesn't support 10Mb Ethernet for audio. Resolutions of 16-, 20-, and 24-bit are supported, and on a hubbed network, up to 64 channels of 20-bit/48KHz audio can be transmitted in either direction in “bundles” of up to eight audio channels.
Buffering of audio at maximum capacity incurs a 5.3ms delay through CobraNet transmitters and receivers, a latency issue that Peak Audio downplays, but which could be a problem for some developers. One of the factors with CobraNet is that latency is cumulative as devices, or nodes, are added to a network — in other words, the more devices the bigger the problem.
However, I should add that CobraNet does support latencies of 2.67ms and 1.32ms at the expense of channel capacity and network design. Lower latency will reduce the number of delivery channels, plus reduce the depth of the network, i.e. the number of switch hops. Transmission is both isochronous, i.e. “same-time” transmission, and asynchronous — useful for material that's not as time-sensitive as audio data, such as stop/start commands. I mention this because standard Ethernet is inherently asynchronous, so it appears that the engineers at Peak Audio found a clever workaround to guarantee isochronous delivery.
Since CobraNet's introduction, the company has put together an impressive roster of amplifier manufacturers that license its technology, including QSC, whose RAVE (Routing Audio Via Ethernet) systems use CobraNet's digital audio transport. QSC has established itself as a leader in remote control of amplification systems, with RAVE products finding a home in the Sydney Opera House, as well as serving three Super Bowls.
QSC's new generation of network audio control, under a software platform called QSControl.net, is available in Basis 922az, a unit that provides amplifier and loudspeaker control, plus configurable DSP over a network administrated through a GUI. Likewise, Rane offers the NM 48 Network Preamplifier, as well as the NM 84 Network Mic Preamplifier, which uses a CobraNet transport to control up to eight microphones in a system.
At this past March's NSCA show, Cirrus Logic (Peak Audio's parent company) announced the availability of CS18101, the initial release of a CobraNet-based microprocessor, allowing manufacturers to embed the technology directly into their systems. Again, while companies like Symetrix will integrate the chip in products for the install market, look for this technology to find its way into the live event world in the near future.
As popular as it is, it's too early to say whether CobraNet will become, or should become, the de facto industry standard. Other companies would beg to differ, obviously. Protocols such as Gibson Lab's MaGIC (Media-accelerated Global Information Carrier), operate over CAT-5, provide up to 32 channels at 32-bit resolution, and support sampling rates of up to 192kHz with very low latency. It's too early to tell if the technology will make a strong impact given CobraNet's strong lead.
One innovation that has been unfairly characterized as not robust enough for pro audio applications is IEEE-1394, commonly referred to as FireWire. Developed by Apple and standardized as 1394-1995 nine years ago, FireWire is a bus for linking digital audio equipment that was very popular in the consumer market when it was introduced. But the consumer world had relatively little interest or need in achieving extremely high-quality jitter-suppression, or handling professional audio sampling rates, and so the initial spec may have been perceived as a handicap by the pro audio industry.
Nevertheless, the FireWire spec continued to develop through trade associations like the 1394TA. In the original spec, FireWire can handle 400Mbps over copper wire with a cable length maximum of 4.5 meters — the longest hop you can take in the bus. Up to 64 devices can be connected to one bus, and all devices must be within 16 hops of each other. Thus, devices can be a maximum of 72 meters apart. Spec updates like 1394b in 2002 brought faster bus speeds — up to 3.2 gigabits per second — and much longer cable lengths became feasible, especially with fiber-optic cable introduced as a possible conduit. (As a reference, cable that can handle 200 Mbps can carry 80 audio channels at 24-bit/48kHz.)
Yamaha first saw potential in FireWire for broader applications that would extend from the MI market to the professional studio, and even the live world. With the development of mLAN (music Local Area Network), Yamaha focused on creating a FireWire-based protocol that would be implemented in its MI line, as well as its digital mixers — basically into any system that could send or receive audio and MIDI to or from another. As with CobraNet and MaGIC, mLAN sends audio and MIDI across the same cable. Eighty percent of bandwidth is devoted to isochronous, or realtime, streaming of data with 20 percent reserved for asynchronous operation, such as for control purposes. Various companies have begun to include mLAN options for I/O, including Apogee, Kurzweil, Otari, PreSonus, and, of course, Yamaha.
One of mLAN's contributions to FireWire is connection management, which facilitates how and when various devices on a bus talk to each other, whether they are a synth, a mixer, a mic pre, etc. Managing the bus can be done via computer program or a dedicated GUI on a piece of gear. It's worth noting that, as with CobraNet and MaGIC, mLAN was designed to exist without a computer. That said, there are current explorations in developing a connection management server that allows multiple users to employ Web-enabled devices to configure mLAN-connected systems.
Over several years, the architecture of mLAN has gone through a major revision that's made it more appropriate for the live market. Bandwidth allocation has been improved, allowing for more dynamic and customizable use of resources over a network. In addition, the future introduction of bridges (slated for 1394.1) will provide the ability to hook up multiple FireWire buses without bus reset issues. This means you will be able to hot-plug a device on one bus without interrupting data flow on the other — thus creating a seamless entry in the middle of a live performance. In fact, one 1394 bus can completely fail without it affecting any other connected busses. As of press time, the release date for 1394.1 had not yet been announced.
Since CAT-5 is so ubiquitous in facilities around the country, it's interesting to note that members of the IEEE are exploring ways of sending FireWire data across long cable runs. While CobraNet clearly leads the market, the growth of FireWire-based devices and increasing flexibility of mLAN-based approaches might challenge CobraNet in the future.
A wireless future?
Don't expect a lot of smaller venues to start adapting facilities for networked digital audio any time soon. We're still in the early days here, and cost/benefit issues are a reality, even though the costs of computer-controlled switching matrices have been going down in price over the last five years. However, larger venues might realize a savings over time, especially as more manufacturers design consoles, mic pres, amplifiers, and loudspeakers that can be fed and controlled via networked systems.
Bandwidth limitations will probably forestall any substantial development in wireless audio networks. However, it's best to not predict. As Mark Twain once said: “Apparently there is nothing that cannot happen.”
Alex Artaud is a musician and engineer living in Oakland. Email him at email@example.com