UPDATED MAY 9, 2006
The Basics of Digital Television
Digital television is here, and it's changing the way we watch and interact with TV. Datacasting, HDTV, Dolby surround soundtracks, and multiple sub-channels of programs are all part of the DTV revolution.
You've no doubt heard that your old analog TV "will be obsolete as of 2006." You're probably wondering just how many hundreds - or thousands - of dollars you'll need to spend to enjoy DTV. Maybe you aren't sure if the end result will be worth all the time, money, and aggravation.
As one of those "early adopters" fortunate enough to observe and participate in the evolution of DTV, I frequently find myself trying to explain to people just what DTV and HDTV are all about. To help you get started, I've prepared this short fact sheet to answer your questions about digital television and HDTV, and cut through all the "hype" and "clutter" you may be hearing.
What exactly is digital television?
DTV is a new all-digital system for transmitting, receiving, and viewing higher-quality television images and stereo (surround) audio.
What are the goals of digital television?
The primary goals are to offer better picture and sound quality through the use of digital signal processing, and to allow the introduction of new digital services such as multicasting (transmitting multiple streams of video on a single channel) and datacasting. The FCC has mandated that DTV signals be freely available over the air in every locality nationwide that has analog television.
How do current TV broadcasts and DTV compare to each other?
There are some similarities. Both use VHF and UHF broadcast frequencies, although some stations may wind up switching frequencies after the full implementation of DTV. Once the transition to digital TV is complete, TV channels 52 through 69 will be re-assigned to other services.
While analog and digital television broadcasts have a modulated carrier wave, the way that signal is modulated is quite different. Analog TV uses an amplitude-modulated (AM) signal for pictures and frequency modulation (FM) for audio, while DTV signals use digital "packets", or bursts of data, to transmit pictures and audio. Three modulation systems are currently being used for DTV:
- The United States uses Eight Level Vestigial Sideband (8VSB)
- Europe, parts of South America, and much of Asia and Australia/New Zealand use Coded Orthogonal Frequency Division Multiplexing (COFDM). Japan has its own variation of COFDM.
- Digital cable television uses Quadrature Amplitude Modulation (QAM).
- Direct broadcast satellite services use Quadrature Phase-Shift Keying (QPSK).
Combination tuners are already appearing that can support one or more DTV modulation standards. An example would be an 8VSB / QAM tuner for off-air and cable reception, or a DirecTV / Dish tuner that supports QPSK and 8VSB.
I've heard that all television broadcasts must be digital by 2009. True?
The FCC's plan for DTV implementation commenced in November 1998 with 26 "pioneer" DTV stations. 40 network DTV stations were supposed to be on air by May 1999, with all remaining commercial and non-commercial stations by May 2003. At this writing (05/06) there are 1566 DTV stations broadcasting, according to the most recent FCC listings. The new “drop dead” date for analog TV to “go dark” is February 17, 2009.
What will happen to my old analog TV set?
Good news! You'll still be able to use it, if it has AV inputs. All current DTV set-top boxes provide at least one down-converted video signal. This is usually composite video or S-video, which connects into the appropriate AV inputs on your TV set. (Don't have AV inputs? Get with the program!) All DTV set-top converter boxes manufactured to date will support older analog TV sets.
In addition, LG Electronics and Thomson have shown low-cost (about $50) DTV set-top boxes that will convert the 8VSB signal to RF-modulated analog or baseband composite video so that older analog TVs will still work after the transition.
How many DTV standards are there? Can you explain them?
There are four basic DTV picture resolution standards.
To start with; our analog TV system makes pictures with about 480 scan lines from the top to bottom of the TV screen that are refreshed 30 times per second. These are actually interlaced (alternating) scan lines - half the picture is traced in 1/60 of a second, and the other half in 1/60th of a second.
The DTV transmission standards do include a digital version of this 480-line, 30 Hz signal known as 480i. The new DTV standards also allow us to draw those 480 lines progressively (480p), or all at once; just like a computer monitor. This 480p system results in a picture with fewer motion artifacts and no visible flicker.
Both 480i and 480p digital signals are considered to be Standard Definition Television (SDTV), for the images they present are not transmitted with any more vertical lines of picture information than the current NTSC system, and will often have the same aspect ratio (4:3). However, 480p images will appear to have improved vertical picture detail over 480I images, thanks to the use of progressive scanning.
Two DTV picture scan rates -- 1080 interlaced (1080i) and 720 progressive (720p) -- are considered High Definition Television (HDTV).
In the 1080i system, 1080 picture scan lines are traced from top to bottom as interlaced fields (540 lines in the first field, and 540 lines in the second). There are 1920 pixels (picture-forming elements) on each line. Therefore, the total image resolution is 1920x1080, or just over 2 million pixels.
The 720p system scans 720 picture lines from top to bottom in 1/60th of a second, to eliminate flicker. There are 1280 pixels on each line, resulting in a total image resolution of 1280x720 or 921,600 pixels.
In the same time interval that one-half of a 1080i image is shown -- or about 1 million pixels -- all of the 720p image will be scanned, or just under 1 million pixels. For this reason, proponents of the 720p system claim that it has the same perceived image resolution as the 1080i system.
Who is using each system?
At present, CBS delivers its filmed and live HD programs in 1080i, as do NBC, PBS, The WB, and UPN stations owned by CBS. Cable and satellite premium networks such as HBO, Showtime, TNT, Discovery HD, HDNet, HDNet Movies, INHD, OLN HD, and NBA TV use the 1080i format exclusively to broadcast movies and special programs.
ABC, Fox, and ESPN HD networks broadcast prime-time programs, live events, and sports exclusively in 720p.
Do I need a special TV set to watch DTV?
Depending on the TV set you have now, you may be able to watch DTV simply by adding an antenna or cable hookup, external DTV receiver, or set-top box (STB).
- An integrated HDTV set is one with a digital TV built-in. These sets, usually branded as “DCR” or “CableCARD” TVs, are widely available, thanks to a series of FCC mandates to include digital tuners. The tuners may be dual-mode; that is, they can tune in both off-air (8VSB) and unencrypted digital cable (QAM) signals. Or, they can function as one-way digital cable sets with the addition of a CableCARD from your local cable service provider.
- If your TV is an older "multimedia" type with progressive-scan inputs for connection to a computer display card or DVD player, you'll be able to watch DTV signals by adding a terrestrial, cable, or satellite set-top box receiver (STB). Depending on the set's scan rate, you'll have compatibility with 480p at minimum, and possibly 1080i and 720p.
- If you have a newer HD-ready TV set with component video inputs (marked "RGB" or "YPbPr") or digital (DVI or HDMI) inputs, you'll be able to watch all DTV formats. However, you won't be able to watch true widescreen TV unless your TV set has a widescreen picture tube or projection screen. Widescreen DTV signals will appear as letterboxed images on 4:3 DTV sets.
Is the difference in image quality that much better in a digital broadcast?
Absolutely! Switching from an analog TV system that is subject to impulse noise, ghosts, color errors, and "snow" to an all-digital system will make a tremendous difference. And it gets even better as image resolution is increased AND the picture aspect ratio becomes wider.
Many people have commented that watching HDTV is like "looking out a window", or "actually being there". That's how good the picture quality is.
What will it cost me to get DTV and HDTV?
If you can find one, a DTV set-top box for terrestrial reception will set you back about $200 - $250, depending on the model. Integrated HDTV sets are priced as low as $700, while larger CRT models range as high as $2,000.
You can also watch DTV on a front projector; LCD, LCoS, and DLP models start as low as $1,000. Plasma TVs can also show DTV signals and the cheapest models start at just under $1,500. 50” plasma monitors can be bought for well under $2,500 – one model is now listing at $2,299. (All prices given as examples are suggested retail.)
LCD TVs are also popular. 32” models can be bought for under $1,200, and there are new models coming out with true 1920x1080 resolution in screen sizes as large as 65”. At present, most plasma TVs are still cheaper than LCD TVs in comparable screen sizes.
There are other ways to watch DTV. Several companies manufacture DTV tuners that plug into a desktop PC, using its monitor (or an external monitor or projector) to show DTV and HDTV signals. These tuners retail for about $200.
A new way to watch DTV is through an Internet Protocol TV (IPTV) set-top box. This is a relatively new service that is slowly being rolled out overseas. Verizon and SBC are working to wire up communities with fiber optics and begin combined voice, data, and video services, using regular QAM format video at first, then transitioning to IP delivery.
If I buy an HDTV-ready set today, will it be obsolete tomorrow?
No. The modulation standards for off-air, cable, and satellite are well. So your integrated DTV set should be just fine for many years. If the compression system changes (such as from MPEG2 to MPEG4), your cable or satellite service provider will likely replace the set-top box at no charge to you.
How about copy protection issues?
Hollywood and the TV networks have asked the FCC to mandate copy protection on set-top boxes and integrated digital TVs. This is intended to keep their content off the Internet and minimize piracy.
One particular digital interface, HDMI (High Definition Multimedia Interface), is part of the plan. HDMI carries video, audio, and control signals as a “one connector fits all” solution between components in your system. The newest implementation, HDMI v1.3, supports all common SDTV and HDTV formats as well as 1080p50/60.
Yet another system, the so-called Broadcast Flag (officially known as the Re-Transmission Control Descriptor) is added to broadcast HDTV signals to prevent them from being copied and distributed on the Internet.
Hollywood has also asked the FCC to eliminate the “analog hole” – the ability for someone to take an HDTV signal from a set-top receiver’s analog component outputs and digitize it for copying and distribution over the Internet.
As you might expect, there is considerable opposition to the broadcast flag and proposals to close the “analog hole”. Advocacy groups like the Electronic Frontier Foundation (EFF), backed by five library associations, Public Knowledge, the Consumer Federation of America, and Consumers Union, previously sued the FCC to block implementation of the broadcast flag mandate – and won.
What about these new high-definition DVD formats?
There are two coming to market. The first is HD DVD, which is supported by Toshiba, NEC, Microsoft, HP, and Sanyo. This uses a blue laser for increased pit density and a constant data rate of 36 Mb/s to stream the video and audio. Movies on HD DVD will be encoded in the 1080p/24 format. As of this writing (May 2006), the output of the players is 1080i/30.
The other system is Blu-ray, backed by Sony, Panasonic, Philips, Mitsubishi, Sharp, Samsung, LG, Pioneer, Dell, Apple, and HP. It also uses a blue-laser recording format that is incompatible with HD DVD. Disc capacity is larger than on HD DVD, but the data rate of 36 Mb/s is the same. Movies will be encoded as 1080p/24, and player output for now is 1080i/30.
Both systems use the HDMI digital interface and Advanced Access Content System (AACS) for digital security. There was talk of down-converting any HD playback to 960x540 through the analog component outputs on HD DVD and Blu-ray players, but significant negative press coverage has prompted several studios (notably Sony) to say that, for now, the analog connections on Blu-ray players will provide full 1080i/30 output.
Will I be able to receive DTV in my area?
The FCC has mandated that DTV broadcasts should cover existing analog TV service areas. In many cases, a small antenna (and possibly an amplifier) will be all you need to receive the signals. Field experience has shown that digital TV signals are usually receivable farther out than analog signals. DTV signals also hold up better at much lower levels than analog.
If you are on cable, your service provider will have different “tiers” of digital TV channels available. Cable system operators are trying to provide at least five HD channels to comply with the FCC’s wishes to move the digital transition along. These could be a mix of local of-air and premium channels, or the five major networks within a given service area.
If you have satellite TV (such as DirecTV and Dish), you'll be able to watch selected DTV and HDTV broadcasts by selecting a satellite-ready STB and subscribing to the appropriate service package – DIRECTV or Dish Network.
Are DVD and HDTV products compatible with each other?
As stated earlier, DTV sets with 480p inputs for DVD players can show 480p DTV broadcasts, and may also be able to show 720p and 1080i. Most DVD players are now coming to market with HDMI output connectors for the newest integrated HDTV sets, but still offer component outputs for older TVs.
What's the difference between the DTV component video standards?
There are two different ways to connect an analog component video signal. The first, identified as "YPbPr", is a three-wire connection. It consists of one luminance signal marked "Y" and two color difference signals marked "Pb" and "Pr". The “Y” input is typically colored green, while the “Pb” and “Pr” jacks are colored blue and red, respectively.
The second standard is identified as "RGB". This can be a three-wire, four-wire, or five-wire connection, and is similar to that used by your computer monitor. In the four-wire RGBS and five-wire RGBHV formats, there are three separate color signals - red, green, and blue - and either one or two sync signals.
Are DTV signals broadcast on special frequencies?
No. DTV broadcasts use exactly the same channels as regular analog television. While many DTV stations are now occupying UHF broadcast channels, broadcasters are allowed to move back to their original VHF or UHF TV channel once the transition to DTV is complete.
The only caveat is that TV channels 51 through 69 will be auctioned off for other uses at the end of the transition to digital TV on February 17, 2009. Stations who originally had analog channels in this band will have to move, no matter what.
One potential problem with re-using low VHF (2-6) TV channels for DTV is the possibility of interference from other signals during certain times of the year. "Skip" may bring in distant broadcasts on the same channel and create interference. Impulse noise is also a problem on low VHF channels. What’s more, the physical size of low VHF and high VHF antennas is much larger than that of a UHF antenna.
Tests so far seem to indicate that high VHF channels (7-13) are quite well suited for DTV broadcasts, and many broadcasters plan to move back to their high VHF channels at the end of the transition. VHF transmitters also cost much less money to operate than UHF transmitters.
Why is it so hard to receive DTV signals in some locations?
When it comes to digital television, it's an "all or nothing at all" proposition. Once the signal is acquired, a steady stream of data assures you'll get a perfect picture and great audio. If that bitstream is interrupted, however, there will be nothing - just a blank screen. It’s as if the signal went over a cliff!
In areas with lots of buildings and multipath, frequent signal dropout causes this "cliff effect". The fix is to use a higher-gain antenna and perhaps even a preamp - assuming the multipath can be tamed. Fortunately, current model set-top (4th generation) and integrated (5th-generation) DTV receivers are light years ahead of early models in terms of multipath performance.
The key to widespread rollout of digital TV is carriage of local DTV stations on cable TV systems. Today, better than 70% of all US households are getting television via cable or satellite, so you can see how important it is for broadcasters and cable/DSS providers to sign carriage agreements.
Is there much to watch on DTV?
You bet! CBS, ABC, NBC, Fox, UPN, and WB carry many or all of their prime-time shows in HDTV. CBS, ABC, Fox, and NBC also carry plenty of live sports programming in HDTV, including college and pro basketball, college and pro football, pro hockey, auto racing, and horse racing. Most of these programs are available with Dolby Digital 5.1 sound.
CBS broadcasts the Grammy Awards and NCA Men’s Basketball Tournament in HD with surround sound, while ABC carries the Academy Awards and Rose Bowl in HD– also with DD 5.1 sound.
HBO, Showtime, Starz, Bravo, INHD, INHD2 and other HD channels present a selection of movies and live concerts/specials in 1080i. HDNet offers sports and special interest programming, and of course ESPN HD and ESPN2 HD cover selected MLB, NHL, NFL, and NBA games in 1080i.
In other words – if you’ve been waiting for “enough HDTV programming to justify buying a new HDTV”, we’re well past that point. It’s time to join in the fun of HDTV!
Where can I go on the Internet to get more information about a specific DTV topic and program schedules?
There are numerous web-based resources you should check out. Here are a few of them. You’ll probably find others as you surf the web.
General DTV information
Information on ATSC standards - www.atsc.org
The latest FCC DTV channel allocation tables, organized by state - www.transmitter.com
FCC FAQs on Digital TV - http://www.fcc.gov/oet/faqs/dtvfaqs.html
Samsung DTV FAQs page – www.samsungusa.com/dtvguide
General DTV information, reviews, antenna tests - www.hdtvexpert.com
Antenna Information - www.titantv.com
DTV Station Updates - www.nab.org
DTV Station Updates - www.100kwatts.tmi.net
High-bandwidth Digital Content Protection - http://www.digital-cp.com
High-Definition Multimedia Interface - http://www.hdmi.org/faq/faq.asp
DVI - http://www.ddwg.org/dvi.html
Broadcast flag - www.mpaa.org/Press/Broadcast_Flag_QA.htm
Electronic Freedom Foundation – www.eff.org
CBS programming – http://www.cbs.com/info/hdtv/
ABC programming – http://abc.go.com/site/hdtvfaq.html
NBC programming - http://www.nbc.com/nbc/footer/HDTV.shtml
WB Programming - http://www.thewb.com/Index/0,7349,,00.html
UPN Programming - http://www.upn.com/
PBS Programming - http://www.pbs.org/digitaltv/dtvsched.htm
Fox programming - http://www.fox.com/schedule/
HDNet programming - http://www.hd.net/
ESPN HD programming - http://sports.espn.go.com/sports/tvlistings/espnhd/index
HBO Programming – www.hbo.com
Showtime programming – www.showtimeonline.com
Discovery HD programming - http://dhd.discovery.com/
