Making the HDTV Connection
Illustration by Turnstyle Imaging There was a time during television's black-and-white era when Andy Griffith's wholesome face dominated the airwaves, entire families dined in front of the tube with TV dinners balanced on their laps, and commercials hawked tasty, refreshing cigarettes. Hooking up your TV back then was easy. You just installed a big antenna on your roof, ran a single wire to a jack on the back of the TV, and voilá-you had up to seven channels of sizzling entertainment. But things are quite a bit more complicated now. TV has entered the digital era, with literally hundreds of channels available on cable and satellite, and digital high-definition TV (HDTV) broadcasts running alongside analog ones in most cities. The changes wrought by digital technology are visible not only on TV screens, but on the back panels of sets as well. New models provide a wide range of video-input options-everything from old-fashioned antenna jacks to computer inputs and digital interfaces that can be used to prevent you from making high-resolution copies of movies, TV shows, and other "content." Most readers of this magazine are familiar with standard types of jacks like composite- and S-video, which we're not going to cover here because they're not relevant to high-def hookups. But if you're looking to buy an HDTV either now or at some point in the near future, it's a good idea to familiarize yourself with the kinds of jacks used for hooking up high-definition tuners, satellite receivers, and cable boxes. We'll give you an overview of HDTV connections, provide a little of the history behind each type of jack, and shed light on the politics behind some of them. It may seem premature to wax nostalgic for the early days of HDTV, but things were definitely simpler back in the late 1990s. For the first few years of the digital TV transition, high-def sets accepted HDTV signals via two types of analog inputs: component-video and RGB. But the Hollywood studios bristled at the idea of sending theater-quality versions of their movies through an analog connection, which a technically adept "pirate" could tap to make copies for mass distribution. Almost immediately, the studios began pushing for a digital interface specifically designed to thwart piracy. Hollywood's collective groaning about analog HDTV connections-and its threats to hold back A-list movies from being aired in high-def-eventually caught the attention of consumer-electronics manufacturers. In July 2001, the satellite TV providers DirecTV and EchoStar (Dish Network) announced support for a copy-protected version of DVI (Digital Visual Interface), a digital connection that had previously been limited to computer systems and displays. Around the same time another digital connection, FireWire (a.k.a. DTVLink or IEEE 1394), designed by Apple Computer for linking personal computers to portable digital devices and hard drives, started to show up on some HDTVs. Not to be outdone on the security front, the 5C consortium, a group consisting of Hitachi, Intel, Matsushita, Sony, and Toshiba, developed its own copy-protection scheme for FireWire connections. Does the arrival of these new copy-protected digital interfaces mean that analog jacks will eventually be phased out? For now, manufacturers are taking steps to ensure that any new HDTV sets and set-top boxes are compatible with existing gear by including wideband (HDTV-capable) component-video jacks or RGB jacks in addition to DVI and FireWire connections. But no matter how things ultimately shake out, knowing which jack does what will be useful when you're shopping for a new set. Let's take a look at each kind. Component Video The most common type of jack for hooking up high-definition TVs to set-top tuners or cable and satellite receivers, component-video connections have three RCA-type connectors color-coded red, green, and blue. Component-video signals can also be routed using BNC and VGA connections, but these configurations tend to be rare. The component-video format was widely used in professional video production before it trickled down to consumer gear when the DVD hit the scene. The term "component video" itself actually encompasses a number of things. When a video camera records an image, it consists of three channels of color information: red, green, and blue. These "components" are compressed into a single channel to form a "composite" video signal for analog TV broadcasting. For digital TV broadcasting, digital satellite transmission, and DVD mastering, however, those three color components are translated into a full-bandwidth brightness channel and two color-difference channels. The reason for this is simple. Keeping color and brightness signals separate prevents cross-color artifacts (the rainbow patterns you sometimes see in a news anchor's striped tie or tweed jacket) and delivers a dramatic boost in quality over composite video, especially in the color portions of images, which look more solid and detailed. It also saves greatly on channel capacity, since the color-difference signals don't carry anywhere near the amount of detail that the brightness signal does. RGB Like component video, RGB signals can be transmitted using a number of different connections, but the two types of jack most often found on HDTVs are VGA (a.k.a. d-Sub-15) and RGB+H/V. You've probably already seen VGA connectors, which are used to link most desktop computers with their monitors. The connectors are shaped like an angular letter D and contain 15 pins. RGB+H/V connections use a quintet of either standard RCA jacks or else BNC jacks-a locking, bayonet-type connector that's found primarily on professional video equipment (as shown in this diagram)-with the five wires bundled together into a single cable for most of their length. Before the high-def era, RGB connections were almost exclusively used for computer-imaging applications, where signals with denser pixel counts and higher scanning rates than standard NTSC video were required. The exceptions were high-end home theater gear like video processors and front projectors, which took advantage of wide-bandwidth RGB+H/V connections to deliver line-doubled images free of visible scan lines. In RGB+H/V jacks, three connectors are used for red, green, and blue picture information, while the other two contain the horizontal and vertical (H/V) synchonization signals that instruct the TV to sequentially "draw" video scan lines across the face of the picture tube. An RGB connection doesn't necessarily provide a performance leap over component video, but its single-cable configuration can make for a neater installation with long cable runs.
DVI (Digital Visual Interface) The new kid on the HDTV connection block (some might call it the neighborhood bully), DVI is a one-way jack that's used to route digital bitstreams from a set-top box to a video display. Physically, it looks like a bigger version of VGA, with a D-shaped connector housing a formation of 18 pins. DVI connections transmit signals in uncompressed form. Since no consumer video decks are capable of recording uncompressed high-def programs, this means no copying. The Hollywood studios, which pushed hard to include DVI jacks on HDTVs, like that idea-a lot!-although it leaves viewers who've become accustomed to time-shifting and creating personal video libraries out in the cold. Digital connections like DVI can offer potential image quality benefits, however, since they eliminate unnecessary digital-to-analog conversion steps for signals being sent to video displays. To further frustrate would-be pirates, the version of DVI found on HDTVs also employs a copy-protection scheme called HDCP (High-bandwidth Digital Content Protection) that was developed by computer chip-maker Intel. HDCP uses an authentication protocol to protect programs from being copied. The device on the transmitting end-an HDTV satellite receiver, for example-must first verify that the device on the receiving end is licensed to accept copy-protected content. If it is, a "hardware handshake" occurs so the program can be transmitted. FireWire FireWire may be a relatively new feature on HDTVs, but it's been kicking around for a number of years in the computer world. FireWire connectors are relatively small and come in both four- and six-pin configurations. Unlike DVI, which was designed for one-way transmission of digital video, FireWire is a two-way connection that can be used to route both audio and video. (On some HDTVs with FireWire, including a few RCA and Sony models, the connection is restricted to one-way transmission.) FireWire establishes communication between multiple devices linked on a home network, and the compressed MPEG-2 signals that it carries can easily be recorded on digital videotape or hard-disk recorders. FireWire connections on digital TVs and set-top boxes support a copy-protection scheme called DTCP (Digital Transmission Content Protection) that's considerably more flexible than the HDCP scheme used for DVI. With DTCP, for example, a movie transmitted in high-def over satellite or cable could be embedded with specific instructions that allow a digital VCR to make one, several, or unlimited copies of the program. But for premium content like pay-per-view movies where greater security is desired, similar codes could be used to block recording altogether. Shopping for an HDTV can be an intimidating experience-especially when you get a look at the profusion of jacks on the back panels of average high-def sets. Yessiree, life has gotten more complex since the days when Andy Griffith patrolled the placid streets of Mayberry. But now that you understand the ins and outs of digital TV connections, you'll be able to walk through the doors of your local electronics store or A/V dealer with confidence.