Designing an audio network


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It's time to design a facility. You need to route and control audio and its related control functions. Today you're faced with a choice: stand-alone consoles or an audio network. It isn't the point of this article to review how radio studios were designed and organized in the old days, but it will be instructional to go over those techniques briefly so that the benefits of newer technology are more clear and evident.

It used to be that you would first decide how many studios were needed on a per-station basis. Typically the answer would be one on-air studio, one production studio, and perhaps another combination studio that could be used as a backup for the on-air room and for less complex commercial production features (such as dubbing agency spots and adding tags). If you had “n” radio stations, you usually just multiplied the number of studios by “n” to get the final studio count.

Based on the studio requirements, you picked a console of the appropriate size.

Typically a production console was more suited to that function. Often they were larger, with more inputs, more output buses and so on. All the equipment that was needed for the particular studio was located in that particular studio — everything from tape machines to CD players to DAT machines to DAWs.

Which would you rather connect? Both can be used to carry multiple signals.

Invariably there was rack space somewhere in the facility that was effectively a terminal for all the studio programs, and likewise a jumping off point to the transmitter site.

After the Telecommunications Act of 1996, more and more radio stations were crammed in to the same space; and for this reason, more and more equipment was shared between stations under the same roof. In the early 1990s ISDN codecs came in to their own, and often landed in the terminal area racks so that they could be shared. Because those codecs had to receive and send audio, sharing them between stations required complex audio switching. Their inherent delay necessitated a mix-minus feed, which complicated things even further. More and more stations started taking satellite feeds for chunks of the day — and those satellite receivers were typically located in the terminal room racks as well.

As facilities grew larger with more stations, the old way of sharing audio resources — such as using DAs and audio switches that were either push buttons or relays — became more cumbersome. New facility builds often included audio routing switchers that, while expensive at the outset, simplified the construction and later provided new levels of convenience and performance that had not been obtained before.

But even with the “older” type of audio routers, radio stations were pretty much built the same way: using a spoke and hub topology. Any studio would be a mini hub with most of the equipment needed on a daily basis located in it. The terminal rack room would be the major hub with cable runs (spokes) going out to all the various studios. The spokes would consist of fat multi-pair cable that was expensive to buy. Each end of the spokes typically terminated on blocks — many times the ubiquitous 66 blocks or something more modern such as ADC Icons or Krone blocks. A large part of the labor going in to any facility build was the installation of these cables and punching down both ends. The design of a studio was typically to overbuild, because the last thing you wanted to have happen was for all the spoke (trunk) pairs to get used up. That was bad.

One of the final parts of the facility construction was the addition of cross-connects to connect the various pieces of equipment to the trunks themselves, making everything talk. Making changes later during the life of the facility involved literally moving wire pairs or adding new ones so that equipment was physically connected to where it needed to be.

Fast forward

The future is here and instead of building individual radio stations we now consider what is known as an audio network. This new term reflects not only the function, but the methodology as well.

With the explosion in computer networking over the last 10 years, audio equipment manufacturers have taken notice of the new ways in which information (whatever that information consists of) is moved from one point to another. The most basic change is that one pair of wires is no longer just assigned to one static function. In the old days, one pair of wires might be used to carry audio from a DA output that was assigned to a remote broadcast line to the on-air studio. With each pair of wires performing only one static function, hundreds of pairs needed to be purchased, installed and punched down.

Figure 1. The basic spoke and hub network places the audio engines in a central location, such as a rack room.
Click image to enlarge.

At least one manufacturer actually makes use of Ethernet to move audio and control signals around. And the era of the audio console might well be coming to a close because many manufacturers now offer control surfaces that, while they look like consoles, are simply human user interfaces for a remotely located routing switcher.

In an audio network, one twisted pair can literally carry hundreds of signals, whether they consist of digitally encoded audio, or control or other ancillary data.

Because communication between nodes of an audio network is done in a digital format, CAT-5, CAT-5E, CAT-6 or even fiber is used for the actual communication. This type of cable is produced on a massive scale, unlike the fat audio cables that are still available. Consequently, the cost of this type of cable is drastically less than that of fat audio cables. Another thing to consider is that it is easy to find plenum-rated data cables, and this simplifies the construction process as well. And if you need to run AES3 audio signals, CAT-5 cable works well.

The addition of routers to a radio facility made more effective use of many of the wire pairs that were originally installed — and the coming of digital audio routers doubled that efficiency yet again (after all, an AES data stream includes left and right channels).

Equipment manufacturers then saw the inherent efficiency of computer networking, and began looking at moving audio around the radio station facility in a similar fashion via fast data streams (in synchronous or non-synchronous modes). What is known as the physical layer in the language of computer networking — the cable types, the connectors and patch bays — could also be used in the transmission of these high-speed data streams.



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