Connect Corner: In & Out

It’s About Time
All digital signals require a clock signal to keep multiple components in synchronization. AESx has the clock signal embedded in the data stream, so a dedicate word clock connection is often not needed for simple systems. AESx components often have word clock I/O for more complex systems.

The output of a digital component is always latent relative to the input. There is an unavoidable delay. Latency is cumulative, and system designers have a “latency budget” that must be observed to avoid timing issues.

Pros:
—“Analog-like” regarding I/O.
—Two channels on one cable.
—High immunity to electro-magnetic interference and ground loops.
—24/48 resolution is lossless with regard to analog I/O.

Cons:
—Potential clocking issues.
—Requires special instrumentation to troubleshoot.
—Due to the high frequency nature of the signal, an impedance match is required between an output and an input.
—Output is always latent – the only variable is “by how much?”

Digital I/O – Data Networks
Once the analog audio signal is digitized, it’s data. Technology has provided some very efficient means of data transport between computers, the most widespread of which is the Ethernet network. Audio-over-Ethernet (AoE) exploits the low cost and ubiquity of data networks to transport audio data. While AESx and its siblings are audio industry-specific, AoE utilizes technology from the Information Technology (IT) industry as a means of audio transport (Figure 6).

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Figure 6: AoE requires the connection of each component to a network switch. The I/O connections are made using a configuration program (e.g., Dante Controller or CobraNet Disco).

The analog waveform is first sampled, and then “packet-ized.” A packet consists of a few audio samples and some additional “meta” data necessary to traverse the data network. The AoE protocol (e.g., CobraNet, Dante, Q-Sys, Ravenna – there are others) assures that the data gets “on” and “off” of the network to produce a contiguous waveform at the receiving end. High-speed networks (e.g. 1000BaseT or “Gigabit”) can transport hundreds of channels. Unlike the “one-way street” AESx formats, a single cable can carry signals in both directions.

It’s Not Audio. It’s Data!
Regarding I/O, it’s a data network and the rules are rigid and established by the IT industry. The user is largely insulated from the complex inner workings of the network, and deployment in smaller systems is relatively plug-and-play.

Audio practitioners must acquire IT skills to deploy large AoE networks. Ideally, an audio-only data network is established using dedicated network switches. Increasingly, AoE may reside on the venue’s backbone with other data traffic such as email, web browsing, point-of-sale, etc. – the so-called converged network. On a converged network, the audio packets must have higher priority than other data traffic. This is called Quality of Service (QoS). A chunk of a large network can be reserved for audio data through use of a Virtual Local Area Network (VLAN). A VLAN requires a more sophisticated “managed” switch than a simple, dedicated network.

Due to the simple wiring, quantity of channels, and low-cost network hardware, AoE has become a very popular digital audio transport. A major difference between AoE and AESx (and its siblings) is that AESx, like analog, is point-to-point, requiring a direct connection between the output and input. AoE is a network, so signals can be routed between any network devices, regardless of where they reside on the network. This provides extreme versatility regarding signal routing for larger venues, campuses, studios, etc.

The audio practitioner must learn the specifics of the AoE “flavor” that they are using. This includes running a control application on a PC to route audio signals, and configuring network switches for the required QoS.