Currently, all over-the-air TV broadcasters in the U.S. use an analog transmission standard called NTSC. The FCC has mandated that all broadcasters begin broadcasting on a second channel using a new digital transmission standard, ATSC. ABC, NBC, CBS, and FOX affiliates in the top 10 markets have already begun digital broadcasts. Affiliates of these networks in the top 30 markets were supposed to be digital by the end of 1999; most of them are now. All remaining commercial broadcasters were supposed to begin digital broadcasts in May, 2002, and public broadcasters in 2003. As of January 2004 there are about 1344 digital broadcasters, out of some 1700 total. Congress hopes that enough people will have access to digital signals by 2006 so that the analog channels can be returned to the government and reassigned (sold) for other uses.
- Interference-free picture - interference doesn't manifest itself as snow or ghosts
- High quality standard definition (SD) pictures - when progressively-scanned , this is as good as progressive DVD
- High definition (HD) pictures - almost as much picture information as a high quality film print, and more than you'll see in a typical theater.
- Wide-screen pictures - shaped more like a movie screen. Aspect ratio of 16:9, compared to 4:3 for analog TV
- Digital 5-channel surround sound - the same as most movie theaters
- Multicasting - the ability to broadcast more than one program simultaneously in a single channel
- Datacasting - the ability to deliver interactive web-like content to your TV or PC
- Spectrum efficiency - broadcast more channels using less radio spectrum and power
There is now enough HD programming that I cannot keep up-to-date with it. Please refer to the
AVS Forum HDTV Programming Synopsis
READ AND SEARCH BEFORE YOU ASK. Most questions have already been answered.
Most digital broadcasters simulcast their analog broadcast on their digital channel for most of the day. In addition, the following high definition programming is available:
The following sites have weekly HDTV program listings
- CBS - schedule . all scripted series, some movies, and some sports are HD.
- ABC . all scripted series, most movies, and some sports are HD. more info
- PBS - schedule . PBS airs a number of HD and wide-screen specials.
- NBC - schedule . most scripted series are HD.
- The WB
- HBO - schedule .
- Showtime - schedule .
- HDNet - schedule
- Discovery HD Theater
- The Movie Channel
- ESPN 2
- Universal HD
- Voom-exclusive channels
A source of DTV signals: The most widely available source right now is over-the-air broadcasts received with an antenna . You can also receive HD programming from DIRECTV, DISH Network, Voom, and many cable systems. Check out my Satellite HDTV section.
A DTV Receiver/Decoder: Several stand-alone DTV decoders cost less than $600. Several sub-$400 PCI receiver cards for use in PCs are available. Some HDTVs incorporate an ATSC receiver/decoder.
A Display: You can use any of the following:
- A regular NTSC TV - the picture will be no better than what you'd get with DVD. For best results, use a TV with an S-VHS (S-video) or component video input.
- A computer monitor - while small, these tend to actually be sharper than most HDTVs. You can use a computer monitor with any decoder that has an RGB output, including the receiver cards for your PC
- An HDTV, typically a rear-projection or direct-view CRT. These can be found for under $1000, but the really big ones cost $3000 and up right now.
- A projector - most have RGB inputs, while some also have DVI or Y Pr Pb inputs.
All of the following will usually result in better reception, listed roughly from most important to least important
It's not strictly necessary to do all of those things, but each one will help. (e.g., if you aren't able to mount the antenna outside, it still helps to have a big antenna and put it as high as you can, like in the attic)
- point the antenna towards the transmitter (the importance of this depends on how directional the antenna is)
- move the antenna higher
- use a bigger, higher gain antenna
- use a more directional antenna
- mount the antenna outside
- use a single run of new RG-6 cable that's no longer than necessary
- don't use an amplifier unless your cable is longer than 100' or unless you are very far from the transmitters. If you use an amplifier, make sure it's very high quality (>$80)
Reception is highly variable by location and terrain. There's no way to know what will work and what won't except to try it and see. If you try something and it doesn't work well enough, try harder.
A bow-tie antenna may work for people very close to the transmitters (<20 miles or so). I recommend the Radio Shack 40" UHF-only antenna otherwise. Most DTV broadcasters are UHF (channel 14 and higher), so you can use a UHF-only antenna in most places.
- More digital broadcasters - all were supposed to be digital by the end of 2003.
- More digital and HD programming.
- Lower-cost DTV decoders. Prices should fall to $200 within a few years.
- Better receivers. Current receivers have problems with multipath interference .
- Enhancements to 8VSB/ATSC. When broadcasters and receivers both take advantage of enhancements, reception is easier.
- Lower-cost and higher-quality HDTVs. It will be several years before we see HDTVs that are capable of displaying all of the picture information in an HD transmission.
- New DTV signal sources - satellite, cable, and consumer formats such as tape and DVD
The ATSC digital TV standard includes several picture formats. All ATSC-compliant displays can show every one of these formats, no matter which the broadcaster chooses to transmit. The display will convert as necessary.
The formats are usually referred to by the number of lines followed by an i or p to indicate the mode, e.g. 480p, 480i, 720p, 1080i. The 480-line formats are considered SD, and the other formats are considered HD. The highest spatial resolution mode is 1080p. Film-source programming such as movies and primetime series are almost always 24 fps. Sports and other programming with lots of movement are best shown at 60 fps.
- 640 x 480 pixels, 4:3, at 24, 30, or 60 frames per second (fps) progressive , or 30 fps interlaced
- 704 x 480 pixels, 16:9 or 4:3, at 24, 30, or 60 fps progressive, or 30 fps interlaced
- 1280 x 720 pixels, 16:9, at 24, 30, or 60 fps progressive
- 1920 x 1080 pixels, 16:9, at 24 or 30 fps progressive, or 30 fps interlaced
FOX, ABC, and ESPN have chosen 720p as their HD broadcast format. Everyone else has chosen 1080i as their HD broadcast format. (Although 24 fps film-source programming could be broadcast in 1080/24p, or at the very least in 1080i with progressively encoded frames, as HBO does)
You cannot judge the resolution of a display device by what scanning modes it supports. E.g., a 1080i display is not necessarily any higher resolution than a 720p display. In fact, most HDTVs today have a resolution of something less than 1 million pixels, i.e., not even as good as the theoretical maximum spatial resolution of 720p.
Both HD modes contain a lot of picture information. You need a very large TV to appreciate this level of detail. At normal viewing distances on a 30" or smaller HDTV, most people cannot tell the difference between HD and 480p.
TVs create a picture by tracing, or scanning the screen in horizontal lines, from left to right, from the top of the screen to the bottom. Interlace means that the TV scans half the screen, just the odd-numbered lines, in the first 60th of a second, and the even lines in the next 60th of a second. Progressive TVs scan the entire screen every 60th of a second.
Interlace was a necessary compromise in the early days of TV. TVs then had no memory, so the CRT vertical scanning rate had to match the transmitted frame rate (or field rate). It would have taken too much radio spectrum to transmit a progressive picture with a high enough frame rate while keeping the resolution high. Interlace allows you to keep the frame rate high while not sacrificing the resolution too much and meet bandwidth constraints.
Digital electronics and memories make progressive TV practical. All computer monitors scan progressively. Non-CRT display technologies such as LCD, plasma, and DLP are inherently progressive.
Interlace scanning artifacts are always present in an interlace picture, and they become objectionable on very large displays. Interlace pictures are also harder to manipulate (pause, scaling, slow motion).
Interlace scanning means that a 1920 x 1080i picture doesn't really have twice the resolution of a 1280 x 720p picture (as you might think by comparing the number of pixels). To compare resolution directly, multiply the number of pixels in an interlaced display by a factor between 0.5 and 0.7. 1080i is still higher resolution than 720p, but the difference will not be pronounced on typical HDTVs. On somewhat large HDTVs, 720p may look better because it doesn't have interlacing artifacts.
Around 1999 there was concern that the modulation used by ATSC, called 8VSB, doesn't perform adequately, especially with indoor antennas. (Modulation is the method by which the digital information is represented in an analog signal that can be transmitted with radio waves) Specifically, 8VSB is susceptible to multipath interference. Multipath interference occurs when the radio signal arrives at your antenna via multiple paths (some reflected) out of sync with each other. In analog TV, this is manifested as ghosting.
Sinclair Broadcast Group, the largest U.S. TV station group, ran informal side-by-side tests that indicated that the then-current generation ATSC receivers performed very poorly indoors (where multipath is worst) compared to the European DTV system, DVB-T. Poor performance means that the antenna must be positioned very carefully for any picture to be received, with reception being impossible in some locations. DVB-T uses a modulation, COFDM, that is designed specifically to avoid the multipath problem, allowing for easy indoor and mobile reception with simple antennas.
Soon after the tests, (summer '99) Motorola and Nxtwave independently announced new 8VSB receiver chips that incorporate powerful equalizers. Both companies claimed that their equalizers eliminate multipath as a reception issue.
Sinclair was prepared to petition the FCC asking that COFDM be allowed as a modulation scheme in the U.S. along side the ATSC's 8VSB modulation. The fervor has subsided considerably, and it looks like there will be no dramatic changes in the US DTV system.
Receivers incorporating the Nxtwave chip do perform better than 1st-generation receivers, but they are far from perfect. The multipath problem can be solved with a brute-force approach. Receivers will improve as chip makers put more transistors in their equalizers. With an ideal equalizer, 8VSB can perform about as well as COFDM. As Moore's law dictates an ever-increasing number of transistors on chips, we can expect performance to increase considerably.
The ATSC, Zenith, and others have proposed backward-compatible enhancements to 8VSB that would improve reception performance. In order to take advantage of these enhancements, both the receiver and transmitter would need to incorporate them.
Be warned that current generation receivers have rather poor equalizers and still don't handle multipath very well. In many circumstances an outdoor antenna and rotor are required to receive signals. A more directional antenna is usually better, but at the expense of needing to be re-aimed when you want to receive stations from a different direction.
Quite a number of cable TV providers now offer HDTV service. The common offerings are HBO, Showtime, Discovery HD Theater, InHD, and a subset of the local digital broadcasters. You can use the HDTV decoder box provided by your cable company, which connects to your HDTV via a Y Pr Pb analog output. Some new TVs are CableCard capable - this means that you can lease a decryption card from the cable company and insert it into your TV so that you can watch using the TV's internal tuner, instead of using a cable box.
DISH Network - typical SD & HDTV offerings. 921 PVR offers hard-disk recording and time-shifting.
DIRECTV - typical SD & HDTV offerings. HDTiVo hard disk recorder
Voom - limited SD offerings, but a full slate of HDTV, including a number of Voom-exclusive channels which are said to be not much more than frequently repeated eye candy.
Discontinued and unsupported:
Unreleased Cards (as of 5-03). Some of these have been released in Korea but not the U.S.
There were products from ATI, Pinnacle Systems, Broadlogic, Creative Labs, Panasonic, and Compaq that never came to light.
PCI receiver card reference designs (several of the above are based on these)