Ethernet-based Audio Routing: A How-to Guide

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So the decision has been made to rebuild old studios, or to perhaps build anew. There are several ways to accomplish this goal, but for our purposes let's say you are leaning towards an audio-over-IP system, even though you haven't really selected the brand. To remove some of the mystery, I'll look at the differences between the products of three manufacturers by designing a hypothetical radio station, and then seeing how the different systems fit in with our ideas about how we want this all to work. The basic specifications for the functionality of this imaginary radio station are outlined below.

Our theoretical radio station:
◊ Two identical studios, built as main and alternate main
◊ Either studio will be able to handle on-air duties including remote broadcasts. Either will be able to operate as an island unto itself on the air.
◊ All audio sources will be available in either studio or in the rack room.
◊ Some dayparts of this station use a combination of satellite audio and automation. During those dayparts, neither studio will be on-air. A mixer of some sort will derive the program, and feed the STL link.
◊ A legacy STL is fed by analog or AES.
◊ There are three remote sources: satellite receiver at the transmitter site, two in the rack room. Each needs its own mix-minus, routable from either studio.
◊ Each studio has a telephone hybrid.

Figure 1. Proposed station architecture. Click to enlarge.

Figure 1. Proposed station architecture. Click to enlarge.

Figure 1 shows the proposed architecture. They are identical with respect to recording and playback, and the automation system is dedicated to its studio. A studio computer records and edits audio, and retrieves audio via the Internet.

Either studio can be selected for the input of the STL switcher, which resides in the rack room. A mixer (real or virtual) is in the rack room to feed specified dayparts of automation plus satellite audio to feed the STL switch.

The router feeds both station STLs, but we'll assume copper from both air studios so that, in the very unlikely event of a core switch failure, the station won't be knocked off the air.

Figure 1b. The proposed rack room. Click to enlarge.

Figure 1b. The proposed rack room. Click to enlarge.

The rack room also contains two local sources for remote broadcasts; both are duplex links that require a mix-minus feed coming from one of the two studios. Obviously those feeds need to be routable, because one person could be doing an on-air shift in one studio, while a remote broadcast goes on in the other studio. Additionally, we have a source coming back from a remotely located satellite receiver that lives at the transmitter site.

Let's investigate ways to build this system based on real hardware.

- continued on page 2

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