Evolution in digital audio
The large HD OB vehicle plays a key role wherever Cologne-based public broadcaster WDR is covering significant events or productions. This truck is the latest of four WDR OB trucks with AURUS control rooms and sets new standards in versatility
You might be tempted to think that the potential for technological progress in digital broadcasting is now all but exhausted. After all, the first big digital OB trucks appeared on Germany's roads over 20 years ago. Since then, the technology has developed steadily, producing much higher performance in smaller footprints and trucks have turned into mobile studios with remarkable space utilization. The introduction of HD has provided the incentive for new evolution. You will not find sensational new concepts or technologies in current OB vehicles, instead the technology continues to develop at a steady if unspectacular pace but at a very high level. This trend can be observed at WDR, the largest of Germany’s public broadcasters. In 2012, WDR’s fleet of TV OB trucks expanded and it is now graced by the impressive HD FÜ4 truck with an AURUS audio control room. As is so often the case, the audio control area occupies only a very small space on the new truck. In contrast, the video area is very generously proportioned including the two slide out side extensions, each more than one metre deep. The available space can be subdivided into different rooms with movable partitions and used in a variety of ways. A small multipurpose room serves as an additional VT area or an audio sub-mix room as required. Various task areas, including for example EVS facilities, can be moved around so that the truck can be adapted flexibly to a wide range of production scenarios.
Routing or Connecting
Flexibility is also essential in audio processing and AURUS provides just that. As a freely configurable audio-mixing console it lies at the heart of the audio system. WDR have already used the console successfully on their SD trucks where it has proven to be efficient and very reliable. The pairing of AURUS and the NEXUS audio network, which is open to any audio format you can think of, demonstrates the flexibility so important in outside broadcasting. The duo are there precisely because of their high degree of rapid adaptability and user-friendliness and not only at WDR.
Another plus is smooth integration into a wide variety of audio environments. On the HD FÜ4, AURUS and NEXUS had to fit seamlessly into a very open and versatile infrastructure. This manifests itself with the extensive audio patchbay in the audio control room. All relevant signals connect to this patchbay and all ports can be configured individually. Werner Menskes, production engineer from WDR's TV outdoor-broadcast department, who is in charge of planning and constructing the OB truck, explains it this way: “In the TV production field, such a patchbay is a critical element in being prepared for any possible situation.” Because for example, it may be necessary to insert additional sources or to change the input of a unit with flexible I/O configuration into an output. Other scenarios include creating extra monitoring points, direct and sophisticated troubleshooting, or even setting up a full fallback configuration rapidly in the event of a failure. All in all, the patchbay provides a total of 1 800 ports which gives a huge increase to the vehicle’s flexibility. The patchbay also provides the intercom ports. Subscriber units can be connected via discreet analogue or digital lines or tunnelled though NEXUS to connected stations. A secondary bay with another 400 ports located in the VT area supports this concept further.
HD FÜ4 at a Glance
VTS Studiotechnik from Eglhausen near Munich was in charge of upgrading the HD FÜ4, a 40-ton articulated tractor-trailer. The trailer features extensions which increase its width more than one metre on both sides. Since the medieval town centre in Cologne, home of the HD FÜ4, has so many narrow streets it is possible to operate the vehicle using just one of the two extensions. When fully extended, the truck provides five rooms – a video monitoring room, a video control room 1, a VT with video control room 2, a audio-control room, and a multi-purpose facility – to accommodate a total of up to 23 people. On the audio side, the truck includes a 48-channel AURUS with a fully equipped audio processor. The associated NEXUS audio network has 128 microphone-input channels. The Magix Sequoia DAW and the Sonic Core EventDriver are used as 5.1-capable playback devices.
Centralized and Distributed Simultaneously
These versatile connection options make it possible to wire the vehicle centrally. When using the traditional approach, the crew lays multicore copper wiring, for example, from the stage microphones to the OB truck. Usually however, the typical NEXUS methodology with distributed audio interfaces is preferred with NEXUS Base Devices placed near the sources, extending the OB truck systems via fibre-optic cables to the location. Here again, WDR has left several options open because in addition to the NEXUS fibre-optic cabling, the truck is equipped with another optical system which can accommodate not only audio but also video, intercom, and data networks. The AURUS architecture is also used to provide maximum flexibility. All the console TFT screens, which display the channel meters in normal operation, can be connected to HD SDI signals alternatively and the central panel display can show the output from the RTW surround monitor unit. The HD FÜ4 has been used in many WDR productions ranging from sports events to recording cultural performances at the broadcaster’s own premises in Cologne. The highlight to date was the semi-final match between Germany and Italy in Warsaw at the 2012 UEFA European Football Championship. The truck generates several concurrent audio mixes, especially at large live events. In addition to the main mix, there is often a clean feed, an M&E feed and or other auxiliary feeds. To ensure smooth and versatile operation, the truck provides a total of four broadcast lines each with 16 audio channels and can be reconfigured to eight broadcast lines each with eight channels if necessary. Thanks to its open bus layout, the AURUS can be configured appropriately for the project in hand depending on the number of buses required. Regarding this feature, Bernd Peters, one of the WDR audio engineers who has completed several productions on the HD FÜ4 is particularly happy with the AURUS down-mix feature: “When we are doing a multichannel production, we use the AURUS down-mix matrix to generate the on-air stereo signal from our multichannel mix in realtime.”
Limiting for Surround Mixes
With so many output signals available, on-air routing becomes a pretty complex business. On the HD FÜ4 this is simplified considerably by a global routing-matrix controller, the BFE KSC-Manager. The STAGETEC system is integrated with this control, so that selecting a transmission line with the KSC-Manager enables the appropriate NEXUS crosspoints automatically.
The levels of the various multichannel mixes should generally be limited using an external dynamics processor. However, only a few compressors and limiters support multichannel linking – the majority of units only support stereo linking, so manual multi-channel linking would be required. Therefore, the WDR follows a different approach and uses a hardware device for the main mix only. For the other sends it uses VST plug-ins instead. The Waves Surround 360° plug-in is suitable for this purpose. It is accessed via Nuendo, one of the few DAWs capable of outputting four multichannel signals. Integrating the DAW with AURUS would enable it and the plug-ins to be controlled from the console directly – this may well be an option for the HD FÜ4 in the future. So there is still room for further progress, the evolution in digital audio continues to produce remarkable innovations – provided these are supported with open and flexible design!