Digital Routing and Mixing

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Here's what to consider in making the TDM vs. AoIP decision.

One definite advantage that AoIP systems seem to have over their TDM cousins is that it is possible to add a computer workstation to the network, and to then have access to its associated audio output and input stream(s) and control logic, for the entire network, by way of the installation of software drivers and network cable. For a TDM system, the alternative way (which is what we've been doing for years) is by installing sounds cards in computers, which can be an expensive proposition with high-end sound cards. A logic control interface from this same computer would likely be done via a serial connection, which of course represents more work and expense in the installation phase. More recently, some TDM manufacturers have developed IP driver interfaces, which eliminates the sound card requirement and serial control connection.

A natural extension of the AoIP network is into the STL portion of your facility. Having a WAN and/or LAN connection at the transmitter site means that devices on that end can become nodes in the system. In practice though, sharing a LAN for STL purposes means either using QoS (and all interim devices must support that along the route) or maintaining a totally separate LAN just for STL purposes.

The final decision

As I mentioned earlier, a TDM-based digital router is really an evolution from the analog router type that many of us grew accustomed to over the years, and as such, it is familiar, tried-and-true technology. If you intend to go with an AoIP system, you'll not only need to learn the details of the new system itself, but you'll also have to become much more familiar with networking in general. In this day and age that is certainly a good thing to do. If you don't already have a good handle on networking, ask yourself if you want to learn that at the same time as an entirely new console type and system type. If networking is just one of your IT skills though, then likely an AoIP system will be something to seriously consider. Finally choosing the type of system might boil down to your design philosophy: Whether you want to centralize the intelligence of the system in your MCR (as with TDM) or whether you want to distribute the intelligence of the system (as with AoIP).

Resource Guide


Audioarts Engineering

Axia Audio


+49 7222 1002 0

   .    .    Qphonics
+49 89-45672-300

Radio Systems

Sierra Automated Systems



Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at

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