You may have noticed that networking has taken over the audio world. Networked audio technology that in the past had been reserved primarily for large-scale installs such as commercial production facilities, stadiums or schools is now being used on tours, in theaters, clubs and even by bands gigging with their own P.A. systems. A basic understanding of audio networking is a necessity — so let’s get into it.
Where’s My Cat?
Most pro audio networks use Cat-5 and Cat-6 “Ethernet” connectivity borrowed from the computer industry. That’s why networked audio is often referred to as AoIP (Audio over Internet Protocol). The ability to adopt Ethernet connectivity was a good thing for the audio industry because we didn’t have to go through the trouble of developing new hardware that could transport multiple channels of digital audio — we simply borrowed existing Ethernet hardware. Fortunately Neutrik (bless their hearts) developed the etherCON connector, which is basically a robust Ethernet connector inside an XLR-style shell. (See Fig. 1.) Don’t try to plug it into an XLR receptacle! At least one type of network, MADI (Multichannel Audio Digital Interface) can use coax or fiber-optic cable.
Network Advantages
Standard Cat-5 and Cat-6 cable is capable of routing multiple channels of digital audio in both directions simultaneously at sample rates ranging from 44.1 kHz/16-bit all the way to 192 kHz/32-bit (and everything in between). MADI networks support 64 channels at 44.1 or 48 kHz/24-bit over coax or fiber. Most networks allow you to “patch” any source to any destination, and can mult a source to multiple destinations — provided your gear has the internal bus structure to support it. Some audio networks support hundreds of channels of digital audio, while others may route only 16. Compare routing 200 channels of audio over a single piece of Cat-5/6 cable versus 200 channels of analog copper snake, and your backache starts to go away. It’s also easier to persuade a contractor into pulling 150 feet of Cat-5 through the ceiling as opposed to 150 feet of 32 pair analog snake. Did I mention that you’ll be able to reconfigure your connections via software, and without moving a single connector?
Given the low cost of Cat-5/6 or coax cable, it wouldn’t be a stretch to carry a spare snake, and I’d daresay that if your Cat-5 digital audio snake had a problem at a show, you’ve at least got a shot at going to an office supply store and finding a replacement. I don’t think you’d have any such luck with a 48-channel analog snake. As audio is transmitted digitally, there’s less chance for signal degradation over long cable runs, as can happen with analog audio.
It’s important to realize that in addition to streaming audio data, all AoIP also transmits and receives word clock data because the rules for digital word clock apply in a network: only one device can be the word clock master, and other devices must sync to that clock. In some cases, you’ll be completely unaware of this issue, like when using networked personal mixers on stage that allow musicians to create their own monitor mixes. In other situations — like when FOH and monitor desks share the same digital audio fed from a stage box — you’ll have to manually set the word clock master and follower device(s) using the console menu for clock settings.
In case you were wondering, there are no pro audio networks operating over Wi-Fi because Wi-Fi doesn’t support the required data density. We’re interested in maintaining a minimum audio resolution of 44.1 kHz/16-bit (“CD quality”), and Wi-Fi currently can’t handle the data traffic created by a high channel count.
All Networks are Not Created Equally
Here’s the bad news: most audio networks are incompatible with one another. Many manufacturers developed their own protocols because they feel they have the edge over other manufacturers. The past few years has seen Audinate’s Dante network rise in popularity. Dante has been licensed by companies such as Yamaha, Midas, Allen & Heath, Avid, Soundcraft, Lectrosonics, DiGiCo, Shure, Sennheiser, Behringer and other manufacturers. For more info on Dante, visit audinate.com.
Also very popular is AVB (Audio Video Bridging), a network developed by the IEEE and adopted by PreSonus (Fig. 2),
MOTU, L-Acoustics, Meyer Sound, BSS Soundweb, Crown and other manufacturers. (For more about AVB, go to presonus.com/learn/technical-articles). Both the Dante and AVB networks support hundreds of channels of digital audio, and we will not debate here which of these is “better” than the other. Other networks include EtherSound, RockNet, CobraNet, Ultranet, REAC, and ACE, some of which are proprietary to a particular manufacturer, and none of which talk to each other. And that’s a drag. It’s a drag because if you weren’t careful you might invest in equipment that doesn’t talk to gear you’d like to purchase in the future.
AES67 to the Rescue
To alleviate this issue, a few years back the AES announced AES67, basically a set of standardized rules for networked audio communication designed to increase interoperability. That’s a fancy way of saying that equipment employing different networks but adhering to AES67 rules will work together. AES67 is slowly being incorporated into existing networks.
One of the buzzwords you’ll hear when learning about audio networking is “scalability,” which refers to your ability to make the system larger while keeping the gear you already own.
Let’s suppose you’re a small independent sound company and you purchase your first digital stage box and console. You can locate the stage box on the (duh…) stage, meaning that you can eliminate some of the analog cable and shorten all of the analog cable — because now you only need analog wire to get to the stage box. The stage box-to-FOH console connection is made using Cat-5/6 or coax cable, which is faster to deploy, easier to hide, lighter and less clumsy.
Next, let’s suppose you’re ready to commit to purchasing a separate monitor console. Chances are overwhelmingly in your favor that the stage box will have a secondary network port that you can simply connect to the monitor desk, enabling the monitor desk to share audio from the stage box.
There are some networks where you’ll need a network “switch” or hub, just like you would if you were creating an office network. However, in this case, the switch would need to be able to route data at a higher speed. (Some manufacturers will specify what brand and model routers “qualify” for the job).
In the future, if you needed a third console for recording, or to add more monitor mixes, you’d be able to connect mixer number three to the network switch, and it, too, would be able to share audio on the network. You’ve expanded your system without the old gear having become obsolete. And that’s always a good thing.
Steve “Woody” La Cerra is the tour manager and front of house engineer for Blue Öyster Cult.
