Know-how

Imagine if you will, a major broadcasting network, building a gigantic new HDTV production center in the Land of Limitless Opportunity. The broadcaster dislikes its name appearing in the technical press, so we’ll just call it The Center. The Center is very cautious about their technical systems, which must be as close to 100 per-cent failsafe as possible. The clear choice: A NEXUS audio network

Today, The Center’s NEXUS is already vast. Currently the system has an amazing 3,962 inputs and 3,472 outputs, making this the biggest NEXUS system installed to date. In the coming year these numbers are set to grow by a further 3,000 inputs and 400 outputs!

Starlight, Star Bright

Two NEXUS STAR routers distribute this galaxy of signals in STAR formation to a total of 23 Base Devices, soon to increase by 4 more. All mission-critical signals, for example from talent microphones in any of the studios or remote locations around the world, are fed via different routes to both STARs for redundancy reasons. Less critical sources are fed to one STAR or the other.

Safety Net of Light

The Center is on air 24/7 around the world – transmission loss isn’t an option! Therefore the System Design majors on redundancy. And this doesn’t end with the deployment of the two STAR routers. Each studio Talent has a main and back-up mic. The two mic signals go to NEXUS microphone input cards in two different Base Devices in the studio’s rack room. For maximum redundancy each Base Device is connected to both STARS via four fibre-optic cable pairs. Each is run in a separate cable raceway through a different part of the building. If a cable is accidentally damaged, the alternative is automatically and seamlessly switched into use. No one watching TV at home will ever know there’s a problem.
In each Base Device and each STAR the two pairs are connected to different cards to add a further level of redundancy. And that’s just for the main mic! The backup Talent mic gets similarly comprehensive treatment with primary and secondary fibres to the main and alternate STARs as well! Not only that, each audio console in each audio control room has two MADI feeds, one from each STAR, and can be routed in parallel on both. It would be really hard to come up with a scenario where at least one mic signal doesn’t make it through to the console!

The Project

In 2003 GMA and Stagetec were approached by National TeleConsultants of Glendale, CA. A NEXUS System was required for a major project. NTC was in the process of designing a new HD TV Production Facility, The Center, for a Client in the Northeast US. This was to be a major expansion of the Client’s existing TV Production and Uplink Complex.

Perpetual Power

Mains power failure can happen in any facility. The Center chose to cover this possibility with dual independent mains feeds, labeled Red and Blue. Each NEXUS rack has at least two power supply units for redundancy so it’s no problem to feed one from Red power and the other from Blue. A failure of either mains feed or one of the PSUs does not interrupt production. In the bigger Base Devices with a larger number of boards, this arrangement is doubled, so two PSUs are fed by Red and two by Blue. Beyond this, the NEXUS power supply rails are constantly monitored. In the event of a failure, regardless of the cause, the NEXUS screens will immediately display an error message highlighting the problem and pinpointing its location.

Mission Control – On-Air Monitor

This emphasis on reliability could be extended to monitoring outgoing transmissions.
NEXUS Matrix 5 software provides logic functions that make this possible. For on-air monitoring, common among European broadcasters, the outgoing signals are returned in parallel to the NEXUS. Similarly, for off-air monitoring the signals from tuners or satellite receivers would be returned. If the signal level at any of these ports falls below an adjustable predetermined threshold, an alarm can be set. This can trigger a message on a PC screen or fire a GPI to switch on a warning lamp. Automatic on and off-air monitoring is especially relevant when there are a large number of outgoing signals making it impractical to listen to all of them.
You can apply this kind of level monitoring to any signal existing in the NEXUS system, not just inputs. Functions such as these are configured with the NEXUS Logic Window, which provides a variety of automatic actions and triggers. A classic example is studio speaker muting whenever a mic channel is opened. Or how about “Return Talkback”? At The Center each Talent mic position has a TALK button connected to a NEXUS GPI input. When pressed, the mic signal is temporarily re-routed to the talkback bus instead of the Console’s input. So each Talent can speak to the production assistant when they need to, secure in the knowledge they won’t be on air.

The Galaxy is Expanding

The Center is a large facility, but it is part of an even larger existing complex. Audio sources are scattered across the area, with production and post-production facilities in many different buildings. The future will bring even more new buildings with yet more audio source and destination requirements. The NEXUS distributed hardware architecture is right at home in this environment. A NEXUS Base Device in each building functions as a transfer station. A single fibre-optic connection to each STAR can provide 128 channels of bi-directional audio; two fibres, 256 signals! This is a big saving on infrastructure cost. And just like in The Center, NEXUS Base Devices can be installed right where the audio is – in each studio’s rack room, audio control room, video server rooms, master control, Comms room, etc. The STAR topology is amazingly efficient in reducing the vast amount of copper cabling associated with a traditional centralized router installation. The bigger the installation gets, the bigger the percentage savings.

Heavenly Reliability

The NEXUS developers’ motto is “Better safe than sorry”. The designers of The Center in the USA took it one step further. Thanks to their dual redundant system design and the NEXUS safety features, System reliability is assured. This system should be as dependable as the sunrise.

Optical Redundancy in the NEXUS

In many NEXUS installations, wiring from the NEXUS Base Devices to the NEXUS STAR is doubled up to provide for a redundant path. With redundant connections like these, the NEXUS transmits every signal from the Base Device over the two parallel lines to the STAR. The STAR then decides which of the two input signals will be used. The NEXUS will normally ignore the secondary redundant signal. However, the parity bits in both signals are constantly monitored to check for data errors. If a check-sum error is detected in the current live signal while the secondary signal is still error-free, NEXUS will automatically switch to the other fibre port within a single sample. The result is an inaudible switch to the error-free signal – this is true redundancy. Naturally, the same redundancy is applied to the return path to the Base Device.