Where Does Your Audio Go?

Here is a common scenario faced by radio stations scattered throughout the country: Station X buys Station Y. The need arises to share resources amongst the two; and shortly after the sale is announced, the engineers are left to figure out just what to do and how to do it.

Rarely will each station be equally equipped. One station may have an excess of ISDN transceivers, while the other has none; one may have a far-ranging RPU system, while the other has nothing but local loops from a telco; one may have a spare satellite dish that would, in fact, be more useful across town. One may have an extra studio that can be used for voice talent, while the other may be short by one studio. One may have an STL shot that the other, across town, cannot see. Similarly, one may have great off-air reception, while the other has nothing but tall buildings in the way.

A little history

In the not-too-distant past, the most practical means by which stations across town could be connected was with leased-lines from the local telephone company. Because of the expense involved, most arrangements like this were strictly single-channel, and by their nature only worked in one direction, which is called simplex.



The patch bay still has useful functions in a facility, but its use as a facility’s main routing system has been superceded.

The most a pair of stations would probably have was one circuit for each direction between the two. About 10 years ago, ISDN transceivers began to appear; they were the first relatively inexpensive means to communicate between facilities. Their functionality was much greater than that of the analog telco circuits, because they could pass audio both directions (full-duplex). This represented a revolutionary change in the way things were done around the radio station. Not only could the audio quality of the connection be altered, but the connection itself could be started and ended as needed. Having the return path for audio from the far-end was just an added feature and at first not crucial. However, soon afterwards, with the passage of the Telecommunications act in 1996 and the subsequent land-rush of radio station consolidation, the ability to communicate between facilities saw rapidly expanding use.

Prior to the explosion in the use of ISDN transceivers, some stations began using leased T1 circuits between facilities, along with the encoder and decoder pairs, and channel banks that became available in the late 1980s. Again, these provided high-quality, full duplex connectivity between stations; many engineers came up with more and more uses for the bi-directional capability.

Once two stations realize that they can effectively share resources, they must come up with the most economical means (that doesn't mean cheap equipment) by which to do it. Typically, any radio station will have a set of remote program sources: satellite receivers, ISDN transceivers, POTS codecs and RPU receivers. In addition, there will be a set of program feeds from each studio on premises and there will be a studio-to-transmitter (STL) link of some sort, as well as an off-air confidence return feed. These circuits are often available in master control — also known as the rack room. Because the circuits are common to this location, it is ideal to house the central switching engine here. Likewise, install remote feeds from and to the remote location in this room.



A facility based on a router located in a rack room provides a simplified audio distribution path. Facility photo by Gary Kline.

There are at least two passive and mechanical means by which this can be accomplished. The first is the good old-fashioned patch bay; the second is a switch-bank. Sources are then patched with the patch bay or a selection is made on the switch bank. In either case, follow the feed with a distribution amp to isolate each destination within the facility. The second aspect to consider is the return audio feedback to the remote location; once again, either the patch bay or a mechanical switch can be used.

Simplicity and economy (meaning cheap) are fine, but perhaps you are inclined to have your station operating in the 21st century, with the latest technology.

Routing switchers

Routing switchers are nothing new, but in the last five years, several manufacturers have added one to their product line, and several new companies have appeared, with routing switchers as their primary product. In the old days, these switchers could only handle analog signals, but today there are multiple products that handle analog, AES digital or some combination thereof. The routing switcher takes the place of a patch bay, mechanical switching and distribution amps.

The idea behind the routing switcher is really quite simple. Any input X can be connected to any output Y. You can think of this as the part that displaces many of the distribution amps. It is possible to have all the outputs fed by any input; and on an output-by-output basis, the input can be assigned individually. This is the part that replaces the patch bay and mechanical switches. Functionally, the router output is similar to the output of a mechanical switch or a feed from a patch bay in that only one input can be assigned to a particular output at a time. However, with the addition of DSP, some routers have the built-in capability to mix functions ahead of an output.



The XM Broadcast Operations Center oversees all the audio routing functions.

Within the facility, control of the routing switcher functions is done in two ways. For starters, there will be a computer connected to the router mainframe via a serial connection. Housekeeping functions, such as input naming, are accomplished in this way. Because the router lives in the rack room, remote control switching functions from the studios are needed, typically by an RS-485 connection over twisted pairs. A remote controller, often referred to as a head, can be placed in the studio, for instance, and it allows the end user to decide what input is assigned to the particular output.

There have been evolutionary changes in the functionality of routers. A typical feature is the ability to route AES data streams. Most of the switchers that are marketed now give the engineer the ability to conveniently switch analog and digital signals within the same router. Another important change is the ability to communicate via TCP/IP. A computer that once served only to talk to the router can now be located on the station's LAN, giving anyone at the station the ability to carry out housekeeping or switching functions.

Putting it in play

A routing switcher can be useful in handling connectivity between two stations that are across town from one another. Putting this idea into practice is really quite simple. The first thing to decide is the actual means by which the stations are connected. If the station can afford a full-time connection, the likely choice will be a service offered by the local telephone company, such as a leased T1 circuit. Count the cost of the encoder and decoder pair, in addition to whatever expense the local telco will charge for installation. If connectivity can only be justified on an as-needed basis, make use of an ISDN transceiver, connecting the inputs and outputs to the routing switcher.



Centralized routing brings a facility’s input and output sources to a single destination, as shown with this installation of a Computer Concepts Epicenter. Photo by Steve Fluker.

Once the connectivity between stations is working, there is the inevitable issue of operating controls on the far end. It used to be necessary to call a colleague at the other station to have him switch the feed. Today, engineers can take complete advantage of a WAN and the efficiency that this technology offers. If the computer that controls the switching function on the far end is on the LAN, remote control can be accomplished with TCP over a private network or perhaps even the Internet.

Going one step further

The functionality of routing switchers has increased dramatically. Using what has become known as an audio engine, engineers now have at their disposal not only routing functions, but also console functions such as mixing. In many cases, the functions of these devices can be remotely controlled, giving the users flexibility in the design of their systems. Both Computer Concepts and Logitek have audio engines at the heart of their router and console systems. The audio engine looks and feels like a router: it is a mainframe that mounts in a rack, and has I/O cards to handle inputs and outputs, along with separate control and communications cards. A user interface, (which was once called a console) is connected to the audio engine with a Cat5 cable. While this is an Ethernet cable, the communication protocol is not. A computer is used to carry out the housekeeping functions and the console functions. Channel input assignments can be assigned on a channel-by-channel basis. The destination of outputs can be changed on the fly, and each channel can be controlled by means of a virtual fader, even by means of a TCP connection.

Perhaps the time will come when the station's need exceeds switching a feed on the far end. The engineer may actually need to access console functions on the far end. Take the same concepts discussed so far and expand on them. One example of this is David Lawrence of the show On-Line Tonight. He recently did this in conjunction with C|NET radio in San Francisco. Aside from his normal show broadcast from 7 p.m. to 10 p.m. PT, he added an early morning show from 3 a.m. to 6 a.m. PT. In this application the Logitek Audio Engine was used.

From his home studio in Washington, DC, Lawrence links with the network at C|NET remotely via a virtual private network (VPN). He then communicates with the computer in San Francisco that has the application Logitek Supervisor running, as well as software used to control several Telos Zephyrs. By way of the remote connection, he would dial out on one of the San Francisco Zephyrs to his own studio unit; this established the duplex audio connection. When it was time for the show, he used Logitek's V-Fader software to control two faders (one was his own feed, and the other was a mix-minus air-monitor return sent back to his studio) on the C|NET Studio A Audio Engine. That is not to say that he was physically running the faders up and down, but his remote application showed him via a graphic user interface (GUI) where the virtual faders were. In this way, he was able to have complete control of the production of his program from Washington, while the studio in San Francisco was silent and empty.

Klotz Digital's Vadis system can be taken one step further. The user interface can be physically separated, and connected via a WAN. An entire console can be controlled remotely. A Vadis system installed in a particular facility will run on its own network. The far-end system, physically removed and running on its own LAN, can be connected to the near-end system with a network bridge (a full T1 has all the data capacity necessary to handle the control functions). Duplex audio connections are made via a separate path. With all of the control information necessary to do so running over the data circuit that bridges the networks, a control surface at the near end can seamlessly take the place of a control surface on the far end.

XM Satellite has built a sophisticated system that makes efficient use of the remote control capabilities of Vadis. The heart of their system, known by the acronym BOC (Broadcast Operations Center), located in Washington DC, is connected to two remote locations. One is the studio facility in New York and the other is the studio facility in Nashville. Audio encoders and decoders are used in conjunction with T1 circuits to provide audio connections between facilities. The Vadis system in each location operates on its LAN segment; the three segments are bridged together to make up a WAN (with yet other T1s). The operator at the BOC is able to click on an icon on the desktop of a computer there, which in turns opens client software that communicates with Nashville or New York. The monitor display seen by the operator in Washington is identical to that seen at the remote locations, and the functionality is completely duplicated. This not only facilitates production, but maintains control from one central point, as well.

Ten years ago, a routing switcher was considered to be a luxury item at a radio station, but with consolidation, the fundamental changes in the way radio stations are operated and programmed, and with remarkable changes in technology, routing switchers have nearly supplanted mixing consoles as the heart and sole of the radio station technical facility.


Irwin is director of engineering for Clear Channel, San Francisco.


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