Know-how

STAR Quality

In the good old analog days, huge audio crossbars and patch bays dominated the switching room. Not anymore. Today, one German broadcaster demonstrates how an entire central audio switching system can be transferred to just two 19" racks – courtesy of a new STAR.

Audio Network

Technically, the NEXUS-STAR is a node inside a decentralized audio network. Locally installed, traditional, NEXUS base devices and digital high-performance devices with MADI interfaces are connected to SWR's NEXUS-STAR. This allows it to distribute the signals in a STAR configuration from any source to any output on the premises.

The NEXUS-STAR provides two interface types: MADI and the proprietary FOC NEXUS format. The latter is usually used for connecting several base devices with one another. Unlike MADI, it is a data interface, rather than an audio interface, designed to manage the networking capability of all connected NEXUS devices. Each NEXUS device is aware of the exact configuration of all other NEXUS units in the network, thus providing remote control of all inputs and outputs from any NEXUS device.

No Networked Control

In most large-scale audio networks, decentralized control is explicitly requested. This was not the case at SWR, or at least not entirely. The FOC link with the ability to remotely control the NEXUS devices was selected only for certain parts of the NEXUS network. These are the connection of external lines, or all the other tasks managed by the main switching room itself. The connections between the main switching room and the control rooms – as well as SWR's so-called basic network, which is used for central jobs such as program transfer or linking to the external studio »Villa Berg« – are controlled via digital audio lines rather than a data line.

The advantage of this connection type is that the control rooms cannot change the settings in the main switching room: neither can an engineer in the production department shut down an on-air line. In addition, local maintenance operations, modifications, or updates cannot affect what is going on at the main switching room. The only connection between the main switching room and the various sub-networks is via a fixed number of MADI lines. The switching room, however, is unaware of the local NEXUS configurations in the studios, which means that the local networks can be expanded ad lib and adapted to new requirements, without the need to upload the new NEXUS configurations to the main switching room every time.

Internal Distribution

The first to go digital at SWR were the control rooms. Old analog rooms were replaced with digital ones, which were in turn connected to the analog switching rooms via MADI. This compact format – 64 sends and returns via one optical pair – comes as standard on all current digital mixing consoles, thus making it the obvious choice in Stuttgart.

SWR currently has six digital control rooms with one MADI link to the main switching room each; three MADI lines remains for future requirements. Seven analog control rooms are also connected to the main switching room via MADI. These control rooms share two NEXUS base devices, which, in addition to their main tasks, also provide local routing capacity. In the same way, the so-called SWR basic network for all the central tasks such as station identification and central program transfer, is connected to the main switching room. Together with the programme selector, a special feature at SWR, nine base devices and seven digital control rooms with 24 MADI lines of 64 channels each, are linked to the NEXUS-STAR in the main switching room. For that, the STAR is fitted with six MADI cards, which means that not even half its capacity is currently in use.

The Programme Selector

How do you implement a simple, yet versatile programme monitoring system in a big broadcasting corporation? SWR found the answer to this question. It used a programme selection system based on the internal telephone system. From 160 locations across the premises, journalists can press a few buttons on their telephones to route the stereo signal of one of the 40 available radio and TV programmes, or any other source provided via the NEXUS network, to their monitor speakers. For the staff, it's that simple, even though technically it is a much more complex system. The telephone commands have to be interpreted by special software, developed by Veith, before the requested signals are routed to the NEXUS. Three base devices have been installed for this monitoring system. In response to the telephone commands, they now route the desired signals to the cable runs that have been around since the good old analog days.

Double STAR

In addition to the internal sources at SWR, there are also external sources and outputs to take into account, such as the link to the common ARD broadcast network (Sternpunkt), and, more importantly, the broadcast lines. These are connected to the STAR network via one base device with NEXUS FOC connectors. The internal »heart« of the SWR audio network therefore comprises a STAR and a normal base device. For safety reasons, and to give maximum flexibility with respect to future upgrades of the main switching room, this core is available in a redundant configuration: two base devices that receive external lines via passive splitters and are connected to the external outputs via priority switchers; and two STAR units connected to the MADI lines on the premises. During normal operation, only one STAR/base device pair is used, while the second can be activated at the press of a button. For the implementation of this specific design, SWR took advantage of a new passive fibre-optic splitter and switch. Both the splitter and the switch take care of distributing the incoming MADI lines to STAR elements and the outgoing MADI lines of the currently active STAR.

Timer for NEXUS

NEXUS – whether with or without STAR – switches audio signals instantly. In a main switching room, however, timerbased connections, with the possibility to book the required lines in advance, are necessary to survive a regular working day. For such timer-based information, SWR uses Veith's RoSy routing system whose predecessor had already proved its reliability with the analog system. RoSy allows for time-specific reservations and carries out collision checks while establishing the booked connections. It automates certain connections, for example the connection of the on-air signal to the required sound processor, and broadcast limiter – before the signal actually reaches the outgoing line. It provides extensive control over the NEXUS by routing stereo signals to two NEXUS channels, producing mono conversions where necessary. RoSy uses its own client/server network. Currently, it is only the main switching room that is fitted with working clients, while monitors in the control rooms allow the engineers to keep track of the current status of outgoing lines. Additional clients can be installed in any control rooms as, and when, necessary. Such clients would allow operators to establish connections from outside the switching room – and to remotely control NEXUS from almost anywhere in the building.

A STAR is Born

For now (spring 2001), NEXUS-STAR is used in parallel with its predecessor, the huge analog Ghielmetti and Siemens matrix. The complex RoSy control is still being tried and tested, and engineers felt it would be foolish to run unnecessary risks.

Yet, even at this stage, the advantages of the new system are already apparent. These are the typical advantages of working with NEXUS: extremely short delays; a compact system; easy maintenance; a high degree of reliability; and a transparent user interface. What is new, however, is the exceptionally vast routing capacity. Says SWR's planning engineer Marc-Oliver Brehm: »The sheer size of NEXUS-STAR allowed us to be generous with our control room links.« A great performer in a modest guise – now there's a real STAR.

Facts about NEXUS-STAR

The NEXUS-STAR is a powerful routing component for largescale audio networks used by the likes of broadcasting corporations, trade fairs and other large installations. The NEXUS-STAR accepts up to 16 plug-in boards, each of which can route 256 audio signals. A fully expanded STAR device therefore provides 4,096 inputs and 4,096 outputs, with over 16 million routing points. To cater for even bigger installations, it is possible to run several STAR devices in cascade. Any input can be routed to any output, while the user can choose between point-to-point and pointto- multipoint connections. The NEXUS-STAR currently supports two interface card formats: the fibre-optic Connection (FOC) for connection to NEXUS units; and boards with four MADI connectors. The MADI format allows the user to directly connect big digital audio systems, such as mixing consoles and multitrack recorders. Like all NEXUS units, the NEXUS-STAR works synchronously. Thanks to its internal TDM technology, the system only generates a brief, constant, delay of a mere six samples for all signals. This low latency makes the system suitable for critical applications, such as live broadcasts. During operation, the entire NEXUS network conducts automatic tests. In the event of a line breakdown, the system automatically switches to a redundant line. Furthermore, all cards are hotswappable, thus providing the highest degree of reliability you can imagine. Yet another advantage of the NEXUS-STAR is that its power requirements add up to a mere 160 W for a fully expanded system, which means that no cooling fans are necessary. Yet when you look at this giant, all you see is a dwarf: the whole powerhouse fits into 6U of rack space and can be installed virtually anywhere.