OB Systems

Outside broadcasts are as varied as any television programming, so the systems used to make the broadcast reflect this variety. The typical OB is sport, but crews have to cope with everything from music events to special state occasions.

The simplest way to make an OB is to take the studio to the venue on wheels — the OB truck. 2006 has seen a resurgence in truck building as broadcasters demand HD and surround sound, especially for premium events. A typical truck has a life of 10 to 15 years, so there is always a trickle of replacement business. HD, however, has led to many fleets looking to invest in new trucks.

It is perfectly possible to update a truck from SD to HD, and at around one-third the cost of a new one. But evolving requirements have meant that most of the latest round of super trucks has been designed from the wheels up for HD production.

Outside broadcasts have special requirements that are not usual in the studio. The subject material, frequently
sport, demands high-speed cameras for slow-motion replays. The other is that cable runs can be very long or even not possible, demanding wireless connections.

Two popular cameras for sport are the Grass Valley LDK23HS and Sony BVP9500. The SD slow-motion cameras have a three-phase output, effectively shooting at 150i or 180i. Technology moves on, and now Grass Valley has released the LDK6200 Super SloMo, which can capture HD at double speed, 100/120i. In addition, Sony is soon to release the 3X HDC-3300.

Camera cables
SD cameras use triax cable to carry power and bi-directional video signals. It has proved to be so ubiquitous that many venues installed permanent cables from camera positions to the truck park. When HD cameras where introduced, triax did not have the bandwidth to carry uncompressed video. There were two ways around this: move to fiber or compress the signal so triax could still be used. Most camera manufacturers now offer a choice of fiber or adapters to use existing triax runs.

Fiber connectors have followed the philosophy of triax and supply power to the camera head over copper, so the system is called hybrid fiber/copper. Although the signal losses are lower in fiber, for both the voltage drop in the power supply is the limiting factor. For very long runs, where cable losses mean that self-power is not possible, you can still use hybrid fiber and power the camera head locally.

The audio fraternity already uses tactical fiber for stage boxes. This fiber is used by the military, so it is rugged and well-tried. The same tactical fiber can be used for camera cables.

HD broadcasts come hand-in-hand with surround sound — and another set of problems. Surround-sound monitoring in a truck is less than optimal. It does mean that the sound area has to be a little larger than a stereo truck.

Most existing backhaul systems are set up for stereo audio, so the transmission of six channels (5.1) needs a sideways look. Dolby has the solution with Dolby E encoding. For recorded events, the use of Dolby E means that a surround mix can be recorded on four-track VTRs like HDCAM, without the additional expense of the HDCAM-SR format (which has 12 audio tracks).

Processing delays
Live events often present timing problems. Many pieces of equipment introduce a frame or more of delay. In the controlled environment of the studio, it is all compensated. An OB may be feeding several client broadcasters. Some may want HD 16:9; others want SD 4:3. Audio could be stereo or surround. Ideally, the truck should feed co-timed audio and video in all formats to client broadcasters.

For the OB with temporary rigs, matching audio and video delays means careful planning. Engineering managers have solved many of the video problems. As an example, early aspect ratio converters had a frame delay. After requests from broadcasters, manufacturers now give the ability to crop from 16:9 to 4:3, with less than a line delay.

Truck design
Although trucks are limited in width, and length and weight end up being much the same size, there is a wide variation in interior layouts. The customer has considerable freedom to choose the layout, even within the restriction imposed by highway regulations. For example, sound can be at the front over the king pin, or at the rear. The sides can expand left and right, or on just one side, and the expansion can be one section or two.

Truck design is an iterative process between the customer, the coachbuilder and the systems integrator. What market the customer is hitting? Is it sport, music events or general-purpose?

With the answers to these questions, dividing the precious floor area can start. There are two common configurations. One is to run the stack longitudinally along the sidewall. This can give a wide stack where a large number of monitors are needed. It also gives visual communications between production, sound and engineering.

The alternate arrangement is a transverse stack and production desk. Before LCDs, this layout had a limited width. With LCD monitors in folding wings, the transverse stack now offers a similar viewing area. The transverse stack also gives more room for production staff.

Picture monitors
One of the biggest changes in recent times has been video monitoring. Except for vision engineering positions, the LCD has replaced the CRT in trucks. Although many engineers have reservations about the picture quality of LCDs, their low weight and small front-to-back dimensions make them an attractive choice for a truck.

Stacks traditionally used a large number of small (9in) monitors, but a 24in LCD with quad split is proving popular for trucks. It displays the same number of sources for a given area as 9in CRTs, but the UMD can be incorporated along with audio level meters without the need for additional hardware in the stack. Some trucks have taken this philosophy further to use multi-viewers with a large display.

The smaller dimensions of the LCD gives truck designers more option for layout. A monitor stack can be built with folding wings so that it can be collapsed when the sides are retracted. This was not feasible with the CRT.

Mixing display types — CRT, LCD and multiviewer — is not without issues. Each display has a different propagation delay. If processing de-lays are not compensated, then a cut on the production switcher can be seen rippling across different display types in the stack. The goal of the system designer is to have a shorter delay through the truck as possible. Long delays can create operational problems. One example is a two-way conversation with the an anchor at the network. It would not make sense to delay the sound monitoring to equal the longest video monitoring path.

OBs make heavy use of iso recording for action replays or for later editing. As a consequence, the recording area is a fair proportion of the total fl oor area of a truck. There is always a limit, so dedicated VTR trucks have to be used for large events. In western Europe, few truck operators equip a truck with VTRs. It is more cost-effective to rent the appropriate number of machines in the format that a job demands. Instead, shelves are cabled for the rental VTRs.

This is not the case in other parts of the world. Megahertz has recently built trucks for Middle Eastern broadcasters. With no local rental market, the trucks have to be fully equipped with VTRs and disk recorders.

The de-rig
Although the cheapest way to make an outside broadcast is to drive in a truck, it is not always possible. To cover foreign events, it may take too long to drive to the venue (and return). It may not be possible to get a truck near the venue. It may be a long-running series, where something more permanent is more cost-effective. So for many reasons, the de-rig represents the alternative to the truck. It can be anything from a few fl ight cases up to a sea container.

Every project is different. Some de-rigs are set up in existing buildings; others are in portable modular buildings rented by the client. As well as technical areas, a large broadcast may need general production offi ces, and these will need monitoring and communications installed.

A de-rig may need pre-wired racks, with routers, talkback matrices, all the equipment found in a truck, or just a few fl ight cases for a fl yaway event. A large system may be custom cabled before shipping and will take two to three days to rig on site.