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Fit out for HD DTV broadcasting

Posted: 18 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:digital? DTV? HD? SD? analog?

The U.S. TV broadcast industry is marching toward an all-digital future. By Feb. 17, 2009, all the high-power analog transmitters will be switched off.

The digitalization of video equipment has been underway since the early 1990s. The majority of cameras, VTRs, production switchers and other studio equipment purchased since then use digital processing and digital interfaces. They may also have analog interfaces to facilitate their integration into legacy analog facilities. The majority of contemporary computer-based video equipment!graphics systems, servers, and nonlinear editing systems, for example!are inherently digital, thus virtually certain to have digital interfaces.

Newly constructed facilities or stations that have undergone major changes in the last few years may have infrastructure that are mostly or perhaps 100 percent digital. However, it is more likely that the station is built around a core that may be 100 percent analog.

During DTV's transitional phase, analog infrastructure has not been a serious liability. This is because standard-definition (SD) analog program service has been the station's primary source of revenue. DTV viewership has been a small fraction of the total. However, when the analog shutoff occurs, stations will derive 100 percent of their revenues from digital services.

Aside from the analog to digital program delivery shift, DTV is producing a shift in the balance of high-definition (HD) vs. SD programming and viewership. A major broadcast network has announced its intention to shift from mixed SD/HD to all HD-affiliate program delivery in Q4 08. Given the savings in delivery costs, it is reasonable to assume the other networks will follow suit. This is a clear indication that the HD feed will be the primary program production and delivery format. If, when and where SD is needed, it will be derived from the HD feed.

The other staples of the TV station's schedule!syndicated programs, locally produced news, public affairs programs and commercials!are also being produced increasingly in HD. In the future, the station's primary channel will be programmed exclusively with HD content. As an indication of this trend, a number of stations that have constructed new "greenfield" facilities have chosen to build them as 100-percent HD.

Speed up migration
To be positioned to successfully compete in the future, serious consideration should be given to migrating as quickly as possible to a core infrastructure that is all-digital, HD-capable, and able to support the origination of multiple program streams.

Most facilities have made a minimum investment in system infrastructure so that they are Advance Television Systems Committee-compliant. This was typically done by passing through local and network HD feeds directly to the DTV transmitter using a small HD router.

The station's routing switcher, along with its associated control system, is the heart of the facility. The core router touches every aspect of the station's workflow including ingest, QC, program preparation, production, post-production and on-air operations. Therefore, it is extremely important to map out an analog-to-digital migration strategy that ensures continuity of all station operations from start to finish.

If the existing core router is all analog or predominantly analog, serious consideration should be given to its wholesale replacement. At the very least, it should be augmented with an HD-capable digital router large enough to handle all the station's current digital sources and destinations. Choose a router platform that can be easily expanded to handle future growth.

A routing system should be designed for all HD operations that can be initially configured as a mix of SD and HD, and that can be flexibly expanded or reconfigured to handle future requirements.

For a router to be truly HD-capable, it must be designed for 100 percent HD operation with additional margin to spare. The entire cross-point core must be able to handle signals with data rates of 1.5Gbit/s and beyond. The frame, motherboard and I/O system must be able to handle HD signals. The power supply and cooling systems must be able to provide the additional power and cooling required for HD.

In addition to HD and SD digital video, the core routing system may need to handle other signal formats including discrete advanced encryption standard audio or machine control. Select a router manufacturer that offers a wide range of products that handle all the necessary formats.

Primary considerations in a router control system include: the degree of flexibility it provides; the ease with which it can be configured and dynamically reconfigured; the number and types of control panels it supports; and the robustness of its design. The routing system is not very useful if it cannot address the needs of the station, or if it cannot provide trouble-free 24/7 operation.

A secondary consideration for a router control system is how well it supports third party routers. This is important if there are legacy routers that will be kept in service.

The cash register
The master control switcher is often referred to as the cash register of the station because its primary function is to manage the transactions!commercial insertions!that generate revenue. In the past, stations had one revenue stream. In the DTV age, there will be multiple revenue streams.

Simple economics dictate the desirability to move from a single channel model to a multichannel model without an undue increase in cost. To achieve this goal, any increase in either the capital equipment cost or the operating cost must be minimized. This translates into a low per-channel cost for the equipment and holds any increase in operational cost to a minimum.

To avoid adding more operators with an attendant increase in operating cost, automation is required. Stations that are not currently automated will have either to add operators or automate if they wish to program multiple channels. Keeping the per-channel capital equipment cost low, an alternative to the traditional approach to master control switchers is needed. The ideal system is one that has been architected with multichannel operation in mind!a modular system that supports multiple channels in a common platform.

The switcher electronics should be flexible enough to support a range of operational requirements. The primary channel may require a full set of features: switching, mixing, multilevel keying, logo insertion and squeezeback. Secondary channels may require only basic functions like switching, mixing and logo insertion. The switcher electronics should be scalable enough to tailor the features of each channel accordingly.

Redundancy and hot swappable system components are also important considerations as downtime in master control can be very, very costly.

In a modern DTV facility, the primary signal core is HD-SDI with 5.1 surround audio, and master control is multichannel capable of delivering a DTV multi-cast to the DTV transmitter.

Signal processing equipment
It has many names!terminal equipment, modular products, glue. Whatever you choose to call it, the miscellaneous bits and pieces that tie the system together are of paramount importance in any facility. Once upon a time, the lowly distribution amplifier was the most common element in this category. Today, it's more likely to be complex functions like frame synchronizers, up/down/cross converters and multipurpose products packaged on a single module.

When choosing processing equipment, it is best to identify one or, at most, two key suppliers. Every manufacturer has its own proprietary platform, module format, and control system. Mixing equipment from too many manufacturers in the same system can be costly in terms of both capital and operating costs.

Prospective suppliers of processing equipment should be evaluated on the basis of the technical performance of their products, the range of products they offer, and how well their products address the sum total of the needs in a particular system.

- Jay Kuca
Director of Product Management

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