Distributed PA On A Fiber Backbone
Australia's Olympic Park, home to the 2000 Summer Games, showcases the future applications of large-scale distributed systems over a fiber optic backbone.

January 06, 2008, by Keith Clark

While the Sydney 2000 Summer Olympic Games are fast becoming a pleasant memory, digital audio and routing technology implemented for the event portends significant and lasting implications.

Perhaps nowhere is this more in evidence than at the Olympic Park campus, which features an extensive public address system running on a fiber-optic backbone, expected to be in operation for at least another decade. Located in Homebush Bay, often referred to as the demographic heart of Sydney, the campus forms a 2.5km circle surround the Olympic Stadium and it includes a dozen other sporting and exhibition venues developed for the games.

From the outset, the campus was designated to remain a permanent fixture, with extensive residential, recreational and retail areas complimenting the athletic facilities. A commercial center for high-tech industry will also emerge, further revitalizing an area that previously had been, among other things, a naval armaments depot and waste dump.

As one of Australia’s premier design and integration firms, The PA People were already busy implementing a complex distributed sound system at the 110,000-seat stadium when summoned by Olympic organizers to have a look at the campus-wide PA system. Chris Dodds, managing director of The PA People, notes that although the fiber optic pipeline had been established to transport audio, lighting and CCTV, along with commensurate control data for each, serious concerns about the audio segment had arisen.

“The client conceived what is best described as a ‘mass transit’-style public address system that would also allow entry of localized source devices to be introduced on the fiber network, with this input distributed to selected zones,” Dodds explains. An attempt to attain the first phase of the project by the previous contracting firm can be quickly summed up as analog audio modulated on the fiber system with limited routing to zones via a single 16-input by 16-output matrix, falling short of expectations in terms of performance quality, flexibility and functionality. This direction scrapped, organizers turned to ARUP Acoustics , a leading Australia-based electro-acoutics firm, as well as The PA People a scant 20 weeks prior to opening ceremonies for a more effective approach.

“Our development of a complex control and routing scenario at the stadium, easy in operation, attracted the interest of the client and they wanted us to create something similar for the campus-wide system,” Dodds says. “We were merging technologies such as Peavey MediaMatrix, Peak Audio CobraNet and Crown IQ with proprietary digital designs from Creative Audio, our sister company, into a comprehensive front-end package. It was fairly obvious that something like this could be adapted quickly for the campus.”

The revised bid on the project was broken down into bite-sized chunks, with four main phases.

Chosen to design and implement all four phases under the direction of ARUP Acoustics, The PA People installed speakers in more than 80 individual audio areas throughout the campus. An extensive set of paging priorities and hierarchies would supply live system-wide paging, live paging to designated zones, pre-recorded message and background music, again system-wide or by select zones, and most notably, local inputs and wireless microphone system inputs scattered throughout the campus, available for localized entertainment, presentations and paging.

Open Platform
In basic overview, the system can be described as a central control front-end networked with several distributed “nodes” via the fiber backbone. But in reality it’s a bit more complicated than that. First, this project marks the first real-world application of Peak Audio’s implementation of Simple Network Management Protocol (SNMP) for addressing all CobraNet devices on the network.

Further, Creative Audio’s latest generation amplifier control/interface module – accommodating SNMP - has been implemented, enabling the dynamic control of CobraNet bundles and channels from the host application.

“Ultimately what this means is that we have an open platform for all CobraNet devices. For the previous installation at Stadium Australia we used Crown IQ software for control of the CobraNet bundles and channels within the amps, but by using SNMP we’ve streamlined the communication process, cutting a layer that’s no longer necessary,” Dodds says. “At a point very soon, I think we’ll also be able to utilize this Peak platform even more efficiently, for example, in terms of matrixing and routing. In this project we have been able to integrate CobraNet products from Peavey, QSC (RAVE) (http://www.qscaudio.com), and our own Creative Audio amplifier modules”

Conceptually, SNMP is simple, yet that belies its sophistication. It has two basic commands: “get a value” and “set a value”. Any CobraNet device on the network runs a piece of software called an SNMP agent, which oversees a collection of variables that represent the state of the device being managed. Within the campus system, the SNMP agents are managed via the Creative Audio software at the system’s central control position.

Control Packages
Officially dubbed the Homebush Bay Operations Center (HBOC), the central control position houses “a conglomeration of computers and bits and pieces that make the whole thing work”, Dodds says. The main audio routing system is a Peavey MediaMatrix 940 running their version 3.1.1 software and outfitted with six CobraNet digital signal processing (DSP) cards.

The heart of the control system, effectively the control server, is an Intel-based PC running under QNX, a ‘real time’ POSIX compliant operating system. This box runs all the processor software such as Creative Audio’s PageServer, which manages all paging requests and priorities, and EventScheduler, which initiates all time-based requests. These two programs also work with the SNMP and MediaMatrix RATC interfaces, which communicate the appropriate requirements to the various amplifier modules and the MediaMatrix itself.

Three additional Intel PCs form the message playback and ‘store and forward’ elements of the system. Each unit is loaded with a new Creative Audio CobraNet-PCI card, capable of simultaneously recording and playing back full bandwidth CobraNet audio. Under control of the WaveDev process, these units supply the playback of scheduled messages and the ability to store and forward live announcements when destination zones are busy. They differ from standard sound cards in that they’re multi-channel and include a direct CobraNet interface.

Messages are created as standard .wav files and are stored on the hard drives of the message PC’s. Capability in this regard is quite impressive, with 24 channels of simultaneous playback capability available along with 8 additional channels dedicated to recording for store and forward, providing an ample queue so that live announcements don’t clash with regularly scheduled messages.

The other primary control element consists of a Windows NT computer, which runs a copy of CobraNet Discovery software along with Crown’s IQ Server. Discovery is the mechanism for assigning IP addresses and managing and updating CobraNet firmware to all system components in the field. All of the CobraNet devices require an IP address to facilitate communication via SNMP. IQ server allows anyone connected to the network with a copy of IQ for Windows to establish communication with the amplifier modules for system setup and monitoring.

“One of the notable things about this system and the SNMP implementation is that in the field, there are 48 local and wireless mic inputs,” Dodds notes. “But in terms of CobraNet channels and traffic, and the size of the MediaMatrix system, we’re restricted to only having 12 of them active at any given time. This means that a key part of the whole management software application is the dynamic assigning of CobraNet bundles and channels addresses to those 12 inputs/wireless mics in use at any given time.”

With the software interface, system operators choose which of these inputs are active, for example, Local Input Node 12 to be active to “x” system zones. When the assignment is made, the software communicates with the CobraNet devices in the designated node, and they provide the commanded routing. “Quite likely, this is the first time that this capability has been done, in CobraNet terms,” he says. “Up to now, everything has been static. But now it’s flexible and dynamic in terms of routing, and this is just the tip of the iceberg, with more to come soon.”

The PA People are currently working on projects incorporating similar capability and more. Dodds conjectures that continued progress could potentially eliminate the need for hardware-based routing and matrixing, to be replaced by an actual on-network matrix utilizing CobraNet.

Analog audio inputs and outputs in the HBOC area are handled by both 8channel and 16 channel CobraNet Audio Bridge (CAB) units from Peavey, while I/O in selected venues use Rave 88 units from QSC. All audio interfaces to the MediaMatrix employs CobraNet, via Peavey’s CobraNet DSP cards.

Distribution & Routing
Distribution around the campus to each node is accomplished via an existing fiber network, which utilizes 3Com 3300 (http://www.3com.com) Superstack network switching. The PA People chose to continue the use of the 3Com equipment for the new CobraNet sound system implementation. (There were 21 nodes for the full-blown Olympic system, with about 24 in the final implementation including feeds to and from venues and other facilities). Separate Virtual Private Networks (VPNs) were implemented across the same physical link to separate CobraNet audio data from control system data.

In the computer room a set of three Superstack switches was implemented with a 3Com ‘matrix module’ backbone between them (two 8-port 100baseFX Fiber switches for the feeds to the nodes and a 24-port 100BaseTX switch for the local equipment). This was then linked to the actual HBOC area (where the operators sit) via a Gigabit fiber link and a second 24-port 100BaseTX switch. At each of the nodes there are 12-port 100BaseTX switches fitted with dual 100BaseFX fiber modules.

Node Electronics and Speakers
Each node houses a 3Com switch and up to six Crown CT- and MA-Series amplifiers each outfitted with the proprietary Creative Audio CobraNet USP/CN amp module. From there, the amplifiers deliver the assigned audio programming to loudspeakers mounted on poles, the majority being weatherproofed JBL Control 28T60’s, with JBL Marquis MS105’s, also weatherproofed, used to cover larger areas. Design of this specific facet of the project fell under the direction of Glenn Leembruggen of ARUP Acoustics, who undertook significant analysis and came up with an electro-acoustic solution that provides hi-fi like reproduction throughout the campus. (A significant quantity of amplifiers and loudspeakers, in addition to extra nodes, were added to the network on a rental basis for coverage to areas such as the Expo during the Olympic Games.)

The Creative Audio CobraNet amp modules also offered additional functionality that proved quite valuable. The modules feature two inputs that may be used to place signals on the CobraNet network. Remote source devices, such as Shure (http://www.shure.com) U4D wireless microphone receivers, can access these inputs via XLR connectors at every node. The inputs also serve as ports for introducing other remote sources onto the network.. As an example, several locations have been outfitted with ambient level control noise sensing microphones that access the MediaMatrix via the amp module inputs and the CobraNet network.

“All nodes also include an Ethernet access point which enables laptop computers to be plugged in for system configuration and control,” Dodds adds. “In such a widespread system, this can be invaluable in terms of convenience, time savings and real-time optimization of any node.”

HBOC Control Room
The HBOC central control position includes 24 touch screen PC’s running proprietary GUI (graphical user interface) software. Part of the contract requirement was to integrate the control of the PA system with the GUI system that was being employed to operate the CCTV and security systems. To facilitate this request Creative Audio wrote an interface so that it could seamlessly communicate with all audio control system software, including PageServer and EventScheduler. A strata of password protection eliminates unauthorized access to key operation parameters.

System operators use the screens to select zones, play messages to zones, or to monitor zones. Live announcements can also be made, when needed. Operators are outfitted with headset interface boxes, devised and built by Creative Audio, that allow them to communicate via phone lines, utilize two-way radio, or make announcements to and monitor the PA system.

Engineering Interface
While the control room operators use the interface described above, the system supervisors manage event schedules and system setup via a special Creative Audio GUI.

This GUI allows for the immediate assignment or time based scheduling of messages, local input assignments and background music; preview of a days scheduled events; control of paging and background music levels; a review of system alerts and alarms; and the allocation of physical areas to paging zones. It also has a password protected section featuring a full-system diagnostic log and other CobraNet diagnostic tools.

Creative Audio’s software design philosophy revolves around the creation and use of core system processes, however in order to meet clients exact requirements a custom GUI is created where required. For example in this project there are no physical paging stations (these being replaced by the HBOC operator interface), so there was no requirement for a paging station configuration page in the GUI.

Looking Ahead
“The biggest risk in this particular project was the extremely short time frame available to complete the work. This gets even more crucial when you look at the number of specialized devices that needed to be fabricated by Creative Audio and then successfully implemented,” Dodds says. “Software development and interface is also not an easy task. So when you look at it, there were four contracts that had to be fulfilled concurrently, each with thousands of variables and custom development to be successfully completed.”

No small charge indeed, yet the system was fully in place and being tested a full eight days before the Olympic Games began. All bugs were eliminated three days prior. About 80 percent of the amplifiers and loudspeakers of the original system remain deployed and in operation, expected to continue into the foreseeable future.

“We see many future applications of what’s been achieved here, particularly for large-scale distributed systems with lots of zones and lots of sources, with potential conflicts needing intelligent system management. Airports and other mass transit facilities, theme parks, Vegas-type attractions – all will benefit from technology of this sort,” Dodds concludes. “We’ll continue our refinement process on each project, and Peak Audio/CobraNet shares the same commitment. It bodes an exciting future.”



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