All about Routers
Apr 1, 2002 12:00 PM, By Conrad Trautmann, CPBE
The term router has multiple definitions, referring to the interface between a LAN and the Internet, a tool used to smooth and round the edges of a surface, or a piece of equipment used to transport analog or digital audio from one place to another. We're interested in the last definition.
The Klotz Vadis audio routing frames at WCBS-AM, New York.
Surprisingly, there are many different companies manufacturing audio routers. Depending on your application, there are few different styles of routers to choose from in varying price ranges. There are three different categories of router design, though some of these do cross over into all of the categories. The first type is the facility router. The second is a stand-alone or small cross-point switcher, usually smaller than a facility router and used in a studio. The third is what seems to be a trend in studio console design where the audio mainframe of a console can be linked to that of another, creating an audio routing system.
Let's first talk about what most people think of as a traditional router. A facility router or mainframe router is used to get an input or a source to some output or destination. Sierra Automated Systems (SAS) and Wheatstone are popular manufacturers of this variety. In a large radio facility, this type of router can be most helpful. The router is most often mounted in the rack room where sources can be wired to the inputs. Then, outputs are wired to individual studios where a remote control head is mounted, allowing an operator to select the source he wishes. In an air studio for instance, common sources on a router would most likely include anything that comes into the building as a remote: traffic, weather, a sporting arena or even other studios. A router can be a lifesaver in a busy facility when there are more inputs needed than a studio console can accommodate on its own. It can also save wiring labor each time a source changes, only requiring the single input to the router to be changed for it to be available anywhere an output of the router is wired. In a large facility like a radio network or multiple station facility with the number of sources and destinations exceeding what could easily be wired through patch bays and cross connects, a router is a necessity. It can help save space as well, especially in a large facility where space is limited.
Facility routers are designed to be the center of a facility�s signal flow and are accessed through many different types of controllers.
Facility routers usually start in larger configurations, such as 32�32, and can expand from there. This means that the router has 32 source inputs and 32 destination outputs. Most routers of this size offer configuration software that is flexible, allowing you to join inputs and outputs for stereo operation. The software can allow multiple users to access the same sources at the same time or restrict the usage if you choose to. A single remote control head can be set to route any inputs to any outputs (commonly called an X/Y head), giving you full control of every source to every destination (e.g. for a radio network), or can be restricted to access all sources to a single destination (e.g. for a single studio). Serial ports on the router can accept external commands from other systems to automate switching of inputs to outputs. Most automation and digital audio delivery systems offer external control commands in an RS-232 or 422 serial format to do just that.
Most facility routers function in the digital domain. This also offers quite a bit of flexibility depending on the input and output cards you purchase. You can continue to use an analog source if you need to, or purchase digital I/O cards to bring your AES signals in direct. Time division multiplexing is used by most digital routing manufacturers to allow you to synchronize external devices to the router to keep signals in synch with each other, similar to the way television times their video signals. It helps prevent clicks and pops during a switch.
More features, more functions
One of the more recent developments in these routers is the ability to split an AES signal into discrete left and right signals in the router. An AES signal is usually a composite signal (left and right combined into a single AES stream), and in older-style digital routers was switched from place to place as a complete signal. Now, companies such as Lighthouse Digital Systems can split the digital composite signal within the router. This allows you to send the left portion of an AES signal to a different destination than the right if you so choose.
Integration of the router and a facility�s consoles is a recent evolution of the technology. Shown here are two examples of audio engines from Computer Concepts and Logitek.
Because digital signals require more bandwidth than analog signals and require a timing reference, these signals are not all that different from a video signal. The benefit of this is that you'll find companies that traditionally market their equipment towards video routing and switching who also have products to route digital and analog audio. So when you're looking at possibly purchasing a new facility router, don't rule out looking at companies like Leitch, Philips and Chyron to provide the right solution for radio. Trilogy Corporation manufactures a facility router that also has intercom heads that integrate the intercom and sources together. In an example of another trend, Trilogy is testing its transmitting voice-over-IP, which uses a dedicated Internet connection to connect intercoms or router heads via a remote Internet connection.
Now that we've covered large facility routers, it leads us to the trend of hybrid audio consoles/router systems. Audio mixing console manufacturers are creating systems that provide a multiple solution product.
Ten years ago, it wasn't unusual to see console manufacturers providing a panel that fit into their consoles that interfaced directly to a facility router. Let's take that idea one step further and make the entire console interface with an external frame of its own that acts as a router. When you consider the function of an audio mixer, it is in effect a small, manual router. Allow those console frames to talk to other frames and you can build a system based on a station's individual needs. You have a facility router that interfaces directly to all consoles in the station. The console acts as the ultimate in router remote control. Wheatstone, Logitek and Klotz are companies that are building systems to do this. Telos Systems has designed a control surface that can be interfaced to an SAS facility router (and others, but we'll look at this in a moment) and in effect does the same thing.
Stand-alone devices can switch a few sources at a time. Some of these units can be linked or controlled remotely.
With this concept, you can start off small, building maybe one studio at a time, and once you've outfitted a few studios with the same type of equipment, you can link them together, accessing any source to any destination. Linking can be done with CAT5 cable or fiber interconnects. All of this equipment is totally configurable to what you need.
Computer Concepts has moved even a step ahead of that, creating Epicenter. This is a facility router that can use an audio console as the router control surface or uses their software-based digital audio delivery system as the controller. Telos' new control surface will work with Epicenter, as will most of the Logitek models of consoles. Or it can be a combination of both. In addition, Epicenter can mix multiple audio formats and sample rates and mix multiple inputs to a single output. You can also add digital effects processing to the audio through Epicenter such as compression, limiting or delay.
Sized to fit the need
Finally, there are many companies that make small routers that can be used in a stand-alone environment such as a studio. They are sometimes called cross-point switchers. These can be 16�1, 16�2, 8�2, etc. These will most commonly be found in-studio and used to solve some problem, such as running out of inputs on an audio console. You might also use it in a studio that is automating a record in a digital audio delivery system. Most can be addressed using a serial connection. Broadcast Tools has a few different models that are designed for such applications. They can be handy in a studio with a digital audio workstation used for production to route different sources into the editor like a CD player or minidisk machine. Some other companies that make these types of routers include Symetrix, Yamaha, and Henry Engineering. In some cases, depending on the manufacturer, these smaller routers also have an interconnect feature that allows them to talk to others of the same brand, adding expansion capability.
Some of the things to look for when purchasing a router should include:
- Does it fit my application? Identify what you are trying to accomplish before doing anything else.
- Does it talk to other equipment (open architecture), or is it a closed system?
- How easy is it to program (user software), and how versatile is it (can it do everything I need it to)?
- What type of security does it have (to prevent users from accessing things they shouldn't, such as switching an on-air channel by accident or restricting access to certain inputs and outputs)?
- Does it offer the features you need, such as the type of remote control head or the ability to split an AES signal or digital signal processing?
- Can it be expanded? With just cards or are more frames needed? What's the maximum it can expand to?
- What type of redundancy does it offer? Multiple CPU control cards, dual power supplies, the ability to save the database to a file?
- Can it interface to an intercom system or provide IFB?
- Can it work over the Internet? (TCP/IP control or transmission)?
As you can see, there are many different types of routers to choose from. If you plan to start from the ground up or simply re-build a single studio, there are some decisions to be made. The good news is that no matter what you decide to do, there is most likely a good solution out there for you.
Trautmann is senior vice president of engineering for Westwood One Radio Networks, New York.