Digital TV & HDTV Primer

High Definition Television (HDTV): The picture is like looking through a clear glass window on a bright sunny day. The high resolution digital picture is so detailed that many will forget they are looking at a television screen.

High Definition Television (HDTV) is actually a subset of the Digital Television (DTV) family of formats, as defined by the Advanced Television Systems Committee (ATSC). DTV uses digital data (1's and 0's) transmission of the picture and sound information, as opposed of the traditional analog signals used for what we know as analog television, devised by the National Television System Committee (NTSC). The relatively new DTV picture formats are generally characterized by the horizontal and vertical resolutions, aspect ratio, interlaced or progressive scanning, and refresh rate (24, 30, 60 times per second).

Vertical and Horizontal Resolution. How many pixels (picture elements) each dimension of the picture holds. For example, 480 lines of vertical resolution means there are 480 horizontal lines of information in the vertical axis. Each horizontal line consists of 640 or 704 pixels lined up.

Aspect Ratio. The ratio of the picture's width to height is expressed as “width:height”. For example, “4:3” aspect ratio means that the picture width is 4 units wide by 3 units high. Another way to express this aspect ratio is “1.33:1”, meaning it is 1.33 times wider than it is high. This traditional aspect ratio is commonly called “full screen”, since it fills the traditional TV screen. In contrast, “16:9” aspect ratio calls for a picture that is 16 units wide by 9 units high, or 1.78 times wider than it is high, or “1.78:1” aspect ratio. This new aspect ratio used by some DTV formats, and by all HDTV formats, is usually called “widescreen” or “16 x 9”. The widescreen format is closer to the movie aspect ratios of 1.78:1 and 2.35:1. Widescreen aspect ratios take advantage of the physiological fact that our eyes have wider horizontal field-of-view than in the vertical direction. By filling more of our natural vision, directors and content producers can better draw us into the action. That's why movie screen have gone to the 1.78:1 and 2.35:1 aspect ratios decades ago. It's a more visually involving experience.

Interlaced or Progressive Scanning. The television picture can be “drawn” in one of two ways. Traditionally, the picture is drawn with two passes, one for the odd-numbered horizontal lines (first frame update), and another for the even-numbered horizontal lines (second frame update). So it takes two passes (or two frame updates) to refresh the entire picture. This is called interlaced scanning. An analog TV picture is completely refreshed about 30 times a second (or 30 Hz). To put it another way, the entire picture is redrawn 30 times every second, with the odd- and even-numbered lines redraw cycle repeated 30 times per second. Some of the new DTV formats call for progressive scanning, where the entire picture (both odd-numbered and even-numbered horizontal lines) is updated in a single pass or scan. Progressive scanning results in a brighter image with no visible TV scan lines and fewer motion artifacts (the stair-step edges that you see on moving objects). Progressive scan correlates better with the film medium, where the entire film cell is protected onto the screen one cell at a time.

Refresh Rate. This is the rate at which the entire picture is redrawn, expressed in number of times per second (or Hz, short for Hertz). DTV supports interlaced scanning at 30 Hz and progressive scanning at 24, 30, and 60 Hz. The 24 Hz refresh rate corresponds nicely with film projection's 24 frames per second (fps) rate.

The table below summarizes all 18 of the ATSC Digital Television formats. There are a total of six (6) HDTV formats, of which 720p/30 and 1080i/30 are the most common. Again, It is important to realize that HDTV is only a subset of the DTV standards, and so DTV is the more general term, while HDTV specifically references the six high definition formats of the 18 DTV formats. The DTV formats are most frequently referred by their horizontal lines of resolution and whether they scan in progressive or interlace (e.g., 480p, 720p, 1080i). The suffix “p” stands for progressive scan, while the suffix “i” stands for interlaced scan. Sometimes, they are further distinguished by their refresh rate, as designated with a slash (“/”), followed by the refresh rate. For example, “1080i/30” refers to 1080 horizontal lines of resolution with interlaced scanning at 30 Hz refresh rate.

Format Index	Vertical Resolution	Horizontal Resolution	Aspect Ratio	Scan Type	Refresh Rate [Hz]	Type
1	480	640	4:3	interlaced	30	SDTV
2				progressive	24	EDTV
3					30
4					60
5		704	4:3	interlaced	30
6				progressive	24
7					30
8					60
9		704	16:9	interlaced	30
10				progressive	24
11					30
12					60
13	720	1280	16:9	progressive	24	HDTV
14					30
15					60
16	1080	1960	16:9	interlaced	30
17				progressive	24
18				progressive	30

Standard Definition Television (SDTV) consists of the first DTV format of 480i/30. It is equivalent to interlaced video output of DVD-Video in 4:3 aspect ratio. This format is used for when bandwidth is a bigger consideration than absolute picture quality. SDTV uses a data rate of about 4-7 Mbps, so three to six SDTV channels can be crammed into the same bandwidth as a HDTV channel.

Enhanced Definition Television (EDTV) is a step up from SDTV, but not quite as good as HDTV. EDTV consists of some 11 formats as shown in the above table. The vertical resolution is limited to 480 lines, but horizontal resolution varies 640 to 704 vertical lines. It encompasses both 4:3 and 16:9 aspect ratios, a number of refresh rates, and both interlaced and progressive scanning. EDTV is used when better picture quality is desired, but without the full bandwidth of HDTV.

High Definition Television (HDTV) uses a data rate of 25 - 27 Mbps for the best possible picture. All HDTV formats are in 16:9 aspect ratio. The 720 vertical resolution only uses progressive scanning, but at various refresh rates. The highest resolution is commonly used in interlaced scanning mode (1080i), due to limitations of current broadcast and consumer equipment. But the format includes 1080p, to accommodate future growth as imaging and display technologies catches up. HDTV is used for premium programming when picture quality is of utmost priority, and bandwidth is less of a concern. This includes select prime time shows, major sporting events, and premium movies.

At its highest resolution, HDTV offers 2,116,800 pixels (picture elements). This is over a six-fold improvement in picture detail of standard definition television which only has 307,200 pixels. Color resolution is also improved by a factor of two. All of the DTV formats use MPEG-2 as the video compression standard, just like DVD-Video. MPEG-2 is a flexible video encoding algorithm and scales up nicely for the higher resolutions of DTV. With digital transmission, there are no analog transmission artifacts and degradations such as snow due to weak signal, double images or ghosting due to multi-path interference of large buildings and structures, and sparkles due to noise from a vacuum cleaner.

Not only does DTV bring us a near-perfect picture, but included in the DTV formats is digital audio as well. Dolby Digital is the standard digital audio encoding format for all DTV formats. Many of you know Dolby Digital for its multi-channel surround sound capability from DVD-Video. What some of you may not realize is that Dolby Digital is more flexible than just a 5.1-channel surround sound format. Dolby Digital is actually a scalable digital audio encoding algorithm that supports 1.0-channel (mono) and 2.0-channel (stereo, with optional Dolby Pro-Logic/Pro-Logic II) when the original programming only has a mono or stereo soundtrack. Dolby Digital only uses as much data as it needs to encode these 1.0-channel and 2.0-channel audio soundtracks.

Home theater fans will realize of course that Dolby Digital can scale up to “6.1” extended surround sound as in Dolby Digital EX. If you are not familiar with surround sound, be sure to read Surround Sound and Home Theater Receiver Buying Guide for more information.

Just like analog TV, Digital Television and HDTV can be delivered in one of four ways:

Over-the-Air (OTA) Broadcasts. Many local broadcasters in large cities and metropolitan areas have already started broadcasting Digital Television and HDTV over the airwaves. Yes, this is old rabbit-ear indoor antenna (and unsightly roof-top outdoor antenna) approach to receiving television signals. What you will need is an roof-top HDTV antenna (if your neighborhood and city code allow for it) or an indoor HDTV antenna to pull in these signals. You will also need an integrated DTV (with a DTV receiver built-in) or a DTV receiver and a DTV monitor (also known as “DTV-ready television”). Alternatively, you can use an DTV receiver and your existing analog TV, but you won’t be able to see DTV and HDTV in its native high resolution formats. In this case, the DTV receiver will down-convert the high resolution DTV signal, scaling it down to a lower resolution that your analog TV can handle. You will get the clear, noise-free digital picture benefits of DTV programming, but you won't see the much-improved high resolution picture due to limitations of your existing analog TV. (This in fact is how many consumers will transition to DTV when analog TV broadcasting stops. )

Fact: More than 861 stations offer over-the-air DTV broadcasts, and 60 percent of Americans are in areas where there at least five stations broadcasting in D TV, as of May 2003.

Broadcast Satellite. Broadcast satellite providers such as Dish Network and DirecTV were relatively quick to provide HDTV channels. If you already have broadcast satellite equipment, you may still need to upgrade your satellite dish to a dual-LNB model (so it can receive from both the HDTV satellite and the “regular service” satellite. You will may also need to upgrade your satellite set-top box so that it can decode the high resolution HDTV signals. Check with your satellite service provider for the specifics. (Note that “digital satellite TV” is not the same as DTV. It is simply the NTSC analog TV signals, transmitted in digital form via satellite, then converted back to analog TV signal for display on your TV set. These “digital satellite TV” signals do not provide any of the true 18 DTV formats, as explained above.)

Terrestrial Cable. For some time, cable TV companies were reluctant to upgrade their infrastructure to provide HDTV. In response to the Federal Communications Commission’s (FCC) strong urging, some terrestrial cable TV providers (e.g., Time Warner Cable) have begun to roll out HDTV channels. With cable TV delivery, you may need a different set-top box, a “QAM-capable” DTV cable receiver, to decode the DTV signals. (QAM stands for Quadrature Amplitude Modulation. Simply put, this is the modulation used to transmit DTV via cable TV. It differs from the 8-VSB modulation used in over-the-air broadcasts of DTV. 8-VSB stands for 8-level Vestigial Sideband.) Some of the newer integrated DTVs incorporate a built-in “QAM-capable” DTV decoder for terrestrial cable, in addition to the 8-VSB DTV decoder for over-the-air reception. The early integrated DTVs only have the latter for over-the-air reception of DTV, and require an additional set-top box for decoding cable delivered DTV programming. Check with your local cable TV provider to see if and when DTV programming will be available. (Note that “digital cable” is not the same as DTV. It is simply the NTSC analog TV signals, transmitted in digital form via upgraded cable equipment, then converted back to analog TV signal for display on your TV set. These “digital cable” signals do not provide any of the true 18 DTV formats, as explained above.)

Pre-Recorded Media. Today, you can view pre-recorded HDTV movies in 1080i on Digital-VHS video tapes using the D-Theater copy protection feature. So far, only DreamWorks, Fox, Universal, and Artisan have embraced this format and released a handful of movies in D-Theater. Read more about this in Digital-VHS and D-Theater Overview.

So what programming is available on DTV, and particularly in HDTV? After all, “content is king” is the mantra of the broadcasting world. Though many networks are national, the availability of these HDTV networks depends a lot on where you live. Here is the information we have compiled. Click on the web links for additional information (links open in a new web browser window).

Major national premium networks (available from cable or broadcast satellite providers):

When the Federal Communications Commission (FCC) auctioned the airwaves that would serve as Digital Television broadcasts back in the mid-1990s, the goal was for the United States to “fully” transition to new ATSC DTV standard by the year 2006. At such a time, Congress would take back the airwaves originally allocated to NTSC analog television and re-allocate it for other purposes. (Not everyone is aware of this fact.) Analog television signals would cease to be broadcast over-the-air, and everyone in the United States would watch Digital Television signals.

To make the huge number of existing analog televisions forward compatible with the DTV signals, manufacturers would make set-top boxes (STB), much like the set-top boxes that you may have today from your cable TV or satellite TV provider, that down-convert the DTV signal to an analog television signal so you would be able to drive your existing analog TVs with a signal that it is able to display. The down-conversion process takes the higher resolution picture of DTV signals and re-formats it to a lower resolution picture that analog TV sets is capable of displaying.

Well, it's already 2003 and the DTV transition has been rather slow to date. Only a few percent of all U.S. households have DTVs or DTV-ready displays. The problem is similar to that of the chicken and the egg. The chicken being DTVs and the egg being DTV programming. Without DTV programming, why would consumers want to upgrade to the more expensive DTVs or DTV-ready displays? From the content producers and broadcasters’ perspective, why would they upgrade their production equipment to DTV when there are not enough consumers with DTV capability to justify the investment?

Given the more realistic rate of DTV rollout by content producers, broadcasters, and distributors, and the adoption rate by everyday consumers, this 2006 “deadline” would have to be extended. The U.S. Congress provision calls for the transition to occur when 85% of the United States population has Digital Television. Your analog TVs are safe from obsolescence for quite a few years.

Naturally, with DTV content available, everyday consumers will want to record such programs whether it be for time shifting, sharing programs, or archival purposes. But recording DTV is one of the sticking points of this new technology. Since DTV, particularly HDTV, contains very high picture quality and its digital form theoretically allows bit-for-bit perfect copies to be made, content owners are leery of allowing their precious, revenue-generating content to be recorded. Most of this is understandable, considering they are the rightful owners. But for sometimes, their resistance may be viewed as just paranoia. As a result, there is ongoing debate as to whether consumers should be able to record certain DTV programs in light of the Fair Use Act.

Whatever the case, recording DTV does have some technical challenges. First, the data rate for HDTV peaks at some 28 Mbps, about four to seven times that of the DVD-Video format. So whatever recording medium is used, it must accommodate a fast data rate. And since many movies and sporting events are a couple of hours long in duration, the recording medium must also have a large data capacity, on the order of 25 - 50 GB.

Digital-VHS (D-VHS). JVC took its aging VHS and Super-VHS formats and gave it new life as a video tape-based DTV recording medium. The Digital-VHS format is capable of recording HDTV in either 1080i or 720p, for up to four hours on a single D-VHS video tape. This recording capability is available now. There are four D-VHS VCRs available, including the JVC HM-DH30000 ($600), Marantz MV8300 ($1,600), Mitsubishi HS-HD1100U, and Mitsubishi HS-HD2000U. For playback of high definition movies, JVC also added a proprietary copy protection feature called D-Theater, allowing movie studios to release movies in full HDTV quality without fear of it being pirated. So far DreamWorks, Fox, Universal, and Artisan have embraced the D-Theater format and have begun releasing a handful of movies to this format. For more information about Digital-VHS and D-Theater, read Digital-VHS and D-Theater Overview.

High Definition Personal Video Recorders (HD-PVRs). Hard disk-based personal video recorders such as TiVo and ReplayTV have revolutionized the way consumers time shift TV. And soon, by the end of 2003 or early 2004, HD-PVRs capable of recording HDTV programming may become available. These devices are likely to be integrated with the set-top broadcast satellite receivers or cable boxes and come with large hard disk capacities, in order to capture the high bandwidth of HDTV programming. Current and previous generations of PVRs are designed for analog TV, and cannot record DTV and HDTV broadcasts.

Recordable High Definition DVD. On the near horizon is the introduction of the recordable High Definition DVD (HD DVD) format. This new optical disc format would use the new blue-violet laser technology to allow more data to be recorded on the familiar 12.0-cm optical disc form factor. Two formats are being considered, Blu-Ray Disc and Advance Optical Disc (AOD). The Blu-Ray Disc format seems to have a leg up on the AOD format, as Sony just released a production Sony BDZ-S77 Blu-Ray Disc Recorder (equivalent $3800 US, available since April 2003) to the Japanese consumer market.

DTVs and DTV-ready displays will undoubtedly get cheaper and better with time. More and more sets will incorporate a built-in DTV receiver. And hopefully with more DTV programming comes more DTV adopters. As we discussed above, HD DVD recorders are only a few years away, providing the convenience of an optical disc format. HD-PVRs based on today's TiVo and ReplayTV devices will probably converge with the new HD DVD recordable format and allow us to archive HDTV quality programming onto removable and shareable HD DVDs.