Networked Audio

Henry Corrado

Networked Parkwide BGM

Until recently, playing background music in large areas required substantial wiring, exposing vulnerable signals to electrical noise and pollution. The second best was independent sound cabinets scattered all over the venue, with little remote control options.

Fortunately, digital technology came to the rescue, allowing even the most modest parks to offer perfect quality background music.

Benefits of Audio Over Network:

Sound Quality
By using digital signal from sources to amplifiers, the signal suffers no degradation even if transported over long distances.

Just a few clicks are needed to reconfigure the park sound system for a special event, or to add a new zone, for example. Paging, announcements, safety spiels as well as zone or park wide events are very complex with an analog system, but quite simple to implement on a networked system.

Users with the right credentials can control Music playback of the whole venue from virtually anywhere. Tablets and smartphones can also be used as interfaces, to control, for example, small shows and street performances. This unified architecture means that even small parks can consider parades and night shows.

It is possible to multiply wiring or route the signal via different paths without facing exorbitant costs.

Network infrastructure is easier and cheaper to implement than heavy speaker wire, not mentioning existing IT hardware might be used.

Brief History
The first standards to be adopted were AES3 in 1985 (2 channels) and AES10 in 1991 (a.k.a MADI, 64 channels on optical fiber).

Since the late 90s, it is possible to carry on a computer network dozens of audio channels and control data (to control park lighting for example). With compatible equipment, sound is carried over the network, from the sources to the amplifiers.

The precursor: CobraNet™
These technologies have evolved with the capacity of Ethernet networks. The precursor was called CobraNet™, a system that transmitted up to 64 digital channels on a single network cable (CobraNet is named after the Shelby Cobra 289GT Racer, not after a snake).

When transmitting sound over a network, the main constraint is to ensure that the audio stream is not disrupted. To achieve this, CobraNet™ ignores some of the integrity controls mechanisms specific to Ethernet, and accommodates a relatively long latency (a few milliseconds), which makes it an unlikely candidate for live music.

CobraNet™ is particularly stable and relatively easy to implement. Even if Cirrus Logic™, the company that developed this technology just announced the end of its development, CobraNet™ remains the de facto standard for theme parks. Fortunately, technical assistance will continue to be available for the numerous users of this protocol

In the 90s, a French company developed "Ethersound" with performances theoretically exceeding those of CobraNet™. EtherSound is designed to make the most of 100 base-T networks, and offers a theoretical latency of 125 microseconds. Despite these specifications, Ethersound never attracted a large number of manufacturers and its adoption has remained relatively confidential.

Audio Networking 2.0
Things have accelerated recently. In less than two decades, the capacity of Ethernet networks has been multiplied by 100, and the design of relatively complex topologies is now accessible to non-specialists.

With larger capacity networks, compromise between quantity of channels, audio quality, and latency is less of a problem. Many players have developed their own standards, sometimes with completely proprietary technologies (Telos , Ravenna, Live Wire, QSC...), sometimes in attempts to federate manufacturers. All these standards are, of course, not mutually compatible.

For a park ready to commit for several decades, the choice is puzzling. Fortunately, a group in the Audio Engineering Society has worked on an interoperability standard called AES67. AE6S7 can be used as a bridge between different networked audio standards, as we’ll see below. Here is a list of networked audio standards, in the order of their theme park audio penetration rate:

QLan is a proprietary system developed by a Californian company called QSC. QSC was known as a leading amplifier manufacturer, but in the past years also became successful in the loudspeaker market, and more recently on processing.

At the surface, QLan appears as a closed system (more on that later) meaning to this day no other vendor offers QLan compatible devices. On a QLan network, all devices (amplifiers, paging stations, interfaces and so on) are manufactured by QSC.

The interesting fact about QLan is that is has been developed by the very same people who initially came up with CobraNet, the ancestor of audio networked system.

AES 67
AES 67 is not a network protocol per se, but an interoperability standard that allows pieces of equipment using different protocols to work together.

In the list of protocols we are reviewing today, QLan and Dante devices can be mixed on a single network. The trade-off is that the sampling frequency is set to 48KHz and resolution to 24bit, which is acceptable for most theme parks applications. Also, discovery and control functions are limited, meaning implementation requires more skills

This standard, developed in Australia by a company called Audinate, takes advantage of the latest network hardware technology: it uses a Gigabit Ethernet infrastructure to carry 256 channels with top quality (96KHz - 24 bits). Dante™ latency is in the two milliseconds range.

Instead of bypassing Ethernet protocol redundancy mechanisms to ensure timely delivery of data, Dante™ uses the concept of "quality of service" developed for network telephony. Audio packets are « tagged » to ensure their priority delivery. Dante™ is theoretically compatible with the audio layer of a new standard called "AVB" (Audio Video Bridging).

AVB is an open standard developed by the IEEE (Institute of Electrical and Electronics Engineers), and is meant to deliver packets of data (audio, video or control) in a timeless manner.

Unlike most other standards, professional audio is not the main market of AVB. It meant to be used in consumer applications such as home entertainment and car electronics.

Because of its possibilities, AVB created high expectations in the audio and specially theme park communities. Unfortunately, AVB require specific networking hardware. In the critical adoption phase, the choice of AVB compliant switches was limited, and the models available not necessarily to the liking of IT people. While this situation seems to improve, designers are left with the second issue which is the lack of AVB compatible equipment.

As early 2018, a handful audio brands have joined the AVB bandwagon (mostly Meyer Sound, Avid, Pivitech, Biamp and MOTU), while dozen of brands offer Dante interfaces. For these reasons, despite promising technical features, it seems that AVB has missed the bandwagon of networked audio in theme parks Networked Audio Hardware

Sending audio to remote areas of the park entails a good-sized network. Two approaches are possible: a physically independent infrastructure or sharing the one used by other data traffic (office computers and other cash registers). In the latter case, the right approach is to create a virtual network (VPN) on an existing fiber infrastructure. Unless the park has serious IT resources, trying to make sound and unrelated data cohabit on the same network will likely result in malfunctions on both sides. In any case, network switches must have configuration capability in order to allow traffic priority, packet tagging and IGMP snooping.

If the network is designed to evolve to AVB, it must be organized around compatible components: AVB certified switches and other network equipment will handshake automatically, simplifying configuration and maintenance.

Whether to use an existing infrastructure or devise one from scratch, due to long distances and required performance level, optical fiber is the solution. Ideally, a loop should be implemented from the central distribution point to local amplifiers cabinets installed in remote areas of the park, not far from the speakers.

Depending on the park size and topology, a single amplifier cabinet may cover several areas. Speaker cables runs can be a couple of hundred meters. Over this distance, it makes more sense to add another amplification cabinet to the network.

Tejix has been using networked audio in all its installations, including the smallest one for the last 15 years or so. The gain in audio quality and flexibility is tremendous. Today, even smaller parks implement modern network infrastructure, and the hardware cost is very accessible. This means parks of all sizes can offer the type of sound environment that was until now reserved to market leaders. CobraNet™, the de facto standard for parks is losing momentum in favor of more modern technologies such as Dante™. With its experience with the successful implementation of large networks, Tejix is a well of information when it comes to implementing attraction or parkwide digital audio;