| When the first high-definition television | | | | It can support high-definition (HDTV) |
| (HDTV) sets hit the market in 1998, movie | | | | broadcasts. |
| buffs, sports fans and tech aficionados got | | | | |
| pretty excited, and for good reason. Ads for | | | | DTV also has one really big disadvantage: |
| the sets hinted at a television paradise with | | | | Analog TVs can't decode and display digital |
| superior resolution and digital surround | | | | signals. When analog broadcasting ends, |
| sound. With HDTV, you could also play movies | | | | you'll only be able to watch TV on your |
| in their original widescreen format without | | | | trusty old set if you have cable or satellite |
| the letterbox "black bars" that some people | | | | service transmitting analog signals or if you |
| find annoying. | | | | have a set-top digital converter. |
| | | | |
| But for a lot of people, HDTV hasn't | | | | This brings us to the first big misconception |
| delivered a ready-made source for | | | | about HDTV. Some people believe that the |
| transcendent experiences in front of the | | | | United States is switching to HDTV, that all |
| tube. Instead, people have gone shopping for | | | | they'll need for HDTV is a new TV and that |
| a TV and found themselves surrounded by | | | | they'll automatically have HDTV when analog |
| confusing abbreviations and too many choices. | | | | service ends. Unfortunately, none of this is |
| Some have even hooked up their new HDTV sets | | | | true. |
| only to discover that the picture doesn't | | | | |
| look good. | | | | HDTV is just one part of the DTV transition. |
| | | | We'll look at HDTV in more detail, including |
| Fortunately, a few basic facts easily dispel | | | | what makes it different from DTV, in the next |
| all of this confusion. In this article, we'll | | | | section. |
| explain the acronyms and resolution levels | | | | |
| and give you the facts on the United States | | | | The ATSC has created 18 commonly used digital |
| transition to all-digital television. We'll | | | | broadcast formats for video. The lowest |
| also tell you exactly what you need to know | | | | quality digital format is about the same as |
| if you're thinking about upgrading to HDTV. | | | | the highest quality an analog TV can display. |
| | | | The 18 formats cover differences in: |
| Analog, Digital and HD | | | | |
| | | | Aspect ratio - Standard television has a 4:3 |
| For years, watching TV has involved analog | | | | aspect ratio - it is four units wide by three |
| signals and cathode ray tube (CRT) sets. The | | | | units high. HDTV has a 16:9 aspect ratio, |
| signal is made of continually varying radio | | | | more like a movie screen. |
| waves that the TV translates into a picture | | | | |
| and sound. An analog signal can reach a | | | | Resolution - The lowest standard resolution |
| person's TV over the air, through a cable or | | | | (SDTV) will be about the same as analog TV |
| via satellite. Digital signals, like the ones | | | | and will go up to 704 x 480 pixels. The |
| from DVD players, are converted to analog | | | | highest HDTV resolution is 1920 x 1080 |
| when played on traditional TVs. (You can read | | | | pixels. HDTV can display about ten times as |
| about how the TV interprets the signal in How | | | | many pixels as an analog TV set. |
| Television Works.) | | | | |
| | | | Frame rate - A set's frame rate describes how |
| This system has worked pretty well for a long | | | | many times it creates a complete picture on |
| time, but it has some limitations: | | | | the screen every second. DTV frame rates |
| | | | usually end in "i" or "p" to denote whether |
| Conventional CRT sets display around 480 | | | | they are interlaced or progressive. DTV frame |
| visible lines of pixels. Broadcasters have | | | | rates range from 24p (24 frames per second, |
| been sending signals that work well with this | | | | progressive) to 60p (60 frames per second, |
| resolution for years, and they can't fit | | | | progressive). |
| enough resolution to fill a huge television | | | | |
| into the analog signal. | | | | Many of these standards have exactly the same |
| | | | aspect ratio and resolution - their frame |
| Analog pictures are interlaced - a CRT's | | | | rates differentiate them from one another. |
| electron gun paints only half the lines for | | | | When you hear someone mention a "1080i" HDTV |
| each pass down the screen. On some TVs, | | | | set, they're talking about one that has a |
| interlacing makes the picture flicker. | | | | native resolution of 1920 x 1080 pixels and |
| | | | can display 60 frames per second, interlaced. |
| Converting video to analog format lowers its | | | | |
| quality. | | | | Broadcasters get to decide which of these |
| | | | formats they will use and whether they will |
| United States broadcasting is currently | | | | broadcast in high definition - many are |
| changing to digital television (DTV). A | | | | already using digital and high-definition |
| digital signal transmits the information for | | | | signals. Electronics manufacturers get to |
| video and sound as ones and zeros instead of | | | | decide which aspect ratios and resolutions |
| as a wave. For over-the-air broadcasting, DTV | | | | their TVs will use. Consumers get to decide |
| will generally use the UHF portion of the | | | | which resolutions are most important to them |
| radio spectrum with a 6 MHz bandwidth, just | | | | and buy their new equipment based on that. |
| like analog TV signals do. | | | | |
| | | | Until the analog shutoff date, broadcasters |
| DTV has several advantages: | | | | will have two available channels to send |
| | | | their signal - a channel for analog, and a |
| The picture, even when displayed on a small | | | | "virtual" channel for digital. Right now, |
| TV, is better quality. | | | | people can watch an over-the-air digital |
| | | | signal only if they are tuned in to the |
| A digital signal can support a higher | | | | broadcaster's virtual digital channel. After |
| resolution, so the picture will still look | | | | analog broadcasting ends, the only signals |
| good when shown on a larger TV screen. | | | | people will receive over the air will be |
| | | | digital. |
| The video can be progressive rather than | | | | |
| interlaced - the screen shows the entire | | | | However, even though a digital signal is |
| picture for every frame instead of every | | | | better quality than an analog signal, it |
| other line of pixels. | | | | isn't necessarily high definition. HDTV is |
| | | | simply the highest of all the DTV standards. |
| TV stations can broadcast several signals | | | | But whether you see a high-definition picture |
| using the same bandwidth. This is called | | | | and hear the accompanying Dolby |
| multicasting. | | | | Digital® sound depends on |
| | | | two things. First, the station has to be |
| If broadcasters choose to, they can include | | | | broadcasting a high-definition signal. |
| interactive content or additional information | | | | Second, you have to have the right equipment |
| with the DTV signal. | | | | to receive and view it. |
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