Digital TV
Digital TV (DTV or DT) is the latest commercial electronics hype, the newest instance of disruptive technology, and a huge source of confusion for anyone familiar with classic TV technologies.
Without regard to the surrounding hype (and when the display is not pixelating), the quality of broadcast DTV really is quite stunning.
Purchasing a classic TV required comparatively few choices, with the screen size being one of the most central considerations. DTV still has that choice of course, but the availability of far larger displays and display technologies makes even that choice more difficult. And, of course, more expensive; the DTV migration is also a huge potential source of profits for the various electronics vendors.
Multiple newer technologies are now competing with more venerable display technologies, including several different projection technologies and two flat-panel technologies. Each has its strengths and weaknesses, of course, and each technology continues to evolve.
Projection
Of the projection technologies, there are configurations with a separate projector and and a display, and there are project configurations where both the light source and the display are combined and built into the same (usually big) box.
Two of the most common projection technologies are Liquid Crystal Display (LCD) and a comparatively new technology that would have made anyone appreciative of truly bizarre ideas and bizarre designs proud, Digital Light Technology (DLT), also referred to as Digital Light Projection (DLP). (Liquid Crystal has been known for a century, but only recently has the technology become a commercially-viable and correspondingly widespread display technology. DLT has only appeared in the last twenty years or so. At the core, DLTs are simple machinery built of levers and mirrors -- but machinery built on the microscopic scale of traditional integrated-circuit electronics. And DLT does work amazingly well.)
LCD technology is most certainly familiar for its use within laptop computers, and projection TVs based on LCD technology shine a powerful beam of light through the LCD, and onto a display. As is common among the various projection technologies, the LCD projector and the display are separate, as with a small portable projector or a larger ceiling-mounted projector, and a large display screen, while other configurations have both the projector and the display integrated into the same box.
DLT replaces the LCD with a very small grid of mirrors, the proverbial really bright light, and a rotating color wheel. The light shines through the color wheel, and a computer rapidly tilts individual and miniscule mirrors to to reflect an appropriately-colored beam toward the display, or away from it. When the mirror reflects the light to the display, that part of the display is illuminated with the color of light that was transmitted through the spinning color wheel.
The central benefit to any of the projection technologies is the comparatively large size of the display, and among the lowest costs for a particular display size. While the high-output projection bulbs do have to be replaced roughly every 2000 to 3000 hours or so, this exchange is generally a comparatively easy operation. Prices and lifetimes of replacement bulbs can and do vary, of course. Oh, and a bulb is a form of vacuum tube. And like all tubes, a bulb is both comparatively hot, and comparatively fragile. More on this later, and particularly as light emitting diode (LED) backlight technologies come on-line -- LEDs are approaching the brightness of strobes.
Most projection TVs will be the most inexpensive option for a particular display size (among the larger sizes), and generally also provide the largest available displays. The most cost-economic choice among the larger displays, in other words.
Projection technologies are sometimes referenced as “MicroDisplay” (or “MD”) technologies. This term is potentially confusing, as the “micro” refers to the size of the projection kernel and not to the size of the display itself.
Direct View
The three most common direct-view displays are CRT, LCD and plasma.
CRT
For well over fifty years, classic TV has used tube technologies -- the oldest of TVs used electronic tube circuitry, producing vast quantities of heat, and were comparatively fragile. Subsequently, most of the tubes were replaced with electronic circuitry using solid state electronics. All statements of “100% solid state electronics” to the contrary, the traditional TV display still contain one large vacuum tube, known as a Cathode Ray Tube (CRT). This CRT is the display. Larger CRTs are also very heavy, with larger CRT technology TVs weighing 100 kilograms (220 lbs) or more. As the solid state electronics have improved, so too has the reliability of the central display tube, and ten-year tube lifetimes are now far from unusual.
At the back of the vacuum tube lurk devices known as electron guns; CRTs work by bending these rays or beams of electrons onto the phosphor coating of the viewing surface of the CRT, causing parts of the display to glow. (If everything works as designed, only the phosphor and not the audience ends up glowing.) The beams are steered by magnetic fields, with the beams scanning horizontally across the phosphor of the display, generating the display as the phosphor glows. One of the more popular designs uses a shadow mask or grill to better target the phosphor illuminated by the beams, providing for excellent displays and those infamous two mask wire artifacts.
The classic CRT TV design causes the beam to scan across the phosphor a total of 480 lines horizontally, scanning every other horizontal line of the display first, and returning to the top and scanning across the alternate lines of the display during a second pass. This two-pass scanning and the alternation of the horizontal display scans reduces the amount of signal processing required, and is known as interlacing. In DTV display lingo, the classic TV display is known as 480 lines interlaced, or Standard Definition TV (SDTV), or 480i. More on this terminology later.
Chief benefits of the CRT are its low price and its outstanding reliability. Call it whatever you want, the CRT is a stable, mature and (now) reliable technology. Even with the tube.
LCD
LCDs are so-called transmissive displays, with the display based on the transmission of a backlight through a filter; through the LCD. Remember when you were younger (back before you could afford a DTV), and shined a flashlight through colored plastic film? That's the basic design for a transmissive display. The plastic film — what gaffers call gels, if you are familiar with the terminology from another industry — is obviously replaced with an LCD layer, and the LCD allows the colors to be changed; the LCD allows the images to be displayed.
Current LCD displays use one or more florescent lights as the backlight, which limits both the total brightness of the display and the difficulty that LCDs have when displaying no colors; when displaying black. (Some light leaks through, producing a grey and not a black area.) Research underway combines the LCD display with light emitting diode (LED) backlights, allowing both bright displays and (theoretically) the ability to selectively darken specific parts of the backlight.
To control the LCD display, the electronics convert the received radio signal of the TV broadcast into addresses on the display; into picture elements or pixels, and switch the individual colors of each pixel on and off. The colors are switched by electronically twisting the crystals within the display, changing how the backlight passes through the particular pixels of the display, and what colors are present.
LCDs have fixed display resolutions, and will either increase or decrease the picture to fit the display, will crop the picture to fit the display, or will display horizontal bars or vertical bars adjacent to the display; will letterbox or will pillarbox the display. Letterboxing looks like rectangular blank bars across the entire width of the top and bottom of the display area, while pillar-boxing has full-height blank bars flanking the sides of the display. (The US Federal Communications Commission (FCC) uses the terms letterbox and barn-door for these blank areas, not that FCC appears to have any particular idea what a barn door actually looks like. The Advanced Television Standard Committee (ATSC) uses the term pillarbox.)
In addition to considerations with the display of black with current-generation backlights, LCD also displays tend to be less easily visible from off-angle. If you are to the right or left, or are viewing the display from an angle above or below the display, the LCD display can be more difficult to see.
Older LCD displays were subject to various display artifacts, including something known as submarining; pixels that could not display faster movement. With faster refresh times and faster pixels available within recent-generation LCDs, the LCD refresh rates can approach those of plasma and CRT displays. This greatly reduces display artifacts, of course. Check the rated refresh time for additional information; lower values are better.
Plasma
Plasma displays are so-called emissive displays, with the display directly resulting from light emitted by the display.
In pragmatic terms, plasma displays are similar to LCDs in that plasma generate the display by directly addressing picture elements (pixels). Unlike with LCDs, the addressed pixels of a plasma display directly produce the light of the display; the pixels are emissive.
Similar to LCDs, plasma displays have fixed resolutions and will adjust the picture to fit the display, will crop the picture, or will letter-box or window-box the display.
The ability to represent dark and black portions of a display are comparatively better with plasma than with LCD, though surprisingly, LCD displays can be brighter than plasma displays. Both aspects due to the emissive nature of plasma, of course.
Like most any other technology, there are and tend to be trade-offs with plasma displays, and one of the more common is the screen-door artifact, where the gaps between the pixels in the array are visible; where the elements are distict, and not blurred together as has been the case with analog TV technologies. Like the mask wires visible on a Sony Trinitron CRT or equivalent shadow mask CRT (or the reel change marks on older multi-reel movies), these artifacts generally aren't noticed until someone points it out to you. (Um. Sorry.)
Mechanical Limits
Within the direct-view displays, there are ranges of physical display sizes, based on the limits of manufacturing, or of mechanicals, or both. CRTs are generally found in low-cost displays, and are seldom larger than about 32 inches due in no small part to the monstrous weight of the larger tube; as mentioned, larger DTV CRTs can weigh upwards of 100 Kg (220 pounds).
LCDs range from 10 inches up to about 45 inches, with the ability to economically manufacture and sell larger displays with sufficiently low defect counts limiting the maximum size. LCD sizes are creeping upward. Plasma displays are generally seen in the 30 to 60 inch range, again limited by the economies of manufacturing, and maximum sizes are also creeping upward.
The size of a projection TV is generally limited by the ability to keep the tube cool and the display bright. A commercial movie theater projector demonstrates a very similar large-scale projection technology, of course, and both front- and rear-projection systems are commonly seen in use in various applications. All-in-one projection units can be large (and quite light, though bulky), while portable or ceiling-mounted projectors can be readily integrated into home theater room environments.
LCD and Plasma displays are generally limited by their respective manufacturing costs, and the resulting prices.
DTV Formats
One of the more confusing parts of DTV are the formats, with somewhere around twenty-eight picture compression formats defined. You don't need to worry about that, however, and really only need to consider the resolution -- 480i, 480p, 720p, 1080i or 1080p. 480i is classic TV resolution and now referred to as SDTV, 480p is EDTV, and all the higher-resolution formats are collectively known as HDTV.
Because of the interlaced nature of formats such as 1080i or 480i, you will see 540 or 240 lines, with the lines scanned and displayed alternately, while 1080p or 720p generates 1080 or 720 lines for each scanning pass, with no alternation. You do get more lines of display with 1080i than with 720p, of course, and some folks prefer this. But in pragmatic terms, look at both a 720p and a 1080i and decide which looks better to you -- and do look at the display refresh rates, as these continue to improve across all displays. You may well have seen creeping lines on progressive-scan displays without realizing the cause of this, as motion of sharp diagonal edges tends not to reproduce particularly well on progressive-scan displays -- you may have seen jagged edges or creeping within the reproductions of the patterns of pinstripe suits or regimental-style ties worn by folks being broadcast, without realizing the cause of the artifacts.
For fixed-size displays such as plasma or LCD, do look specifically at the native format of the display as compared to 1920 by 1080, or 1280 by 720. SDTV and EDTV resolutions are obviously interesting than HDTV, but — if you are considering acquiring such a display — do confirm the full resolution there, too.
The closer a native format matches a DTV format, the better.
Native displays that do not match one of the DTV resolutions will have to be clipped, either letter-boxed or window-boxed — unused and usually black areas of the display comprised of either horizontal bars at the extreme top and bottom of the picture, or of unused vertical bars at the extreme left and right sides of the displayed picture, respectively — or scaled to fit the native display. Cropping simply cuts off the right and left or top and bottom portions of the picture, letter- or window-boxing leaves a portion of the display unused, and (non-multiple) scaling distorts the picture. More than a few commercial offerings do not support a DTV native height and/or native width.
Again, the closer the native resolution of the display is to one of the native ATSC formats, the better. Displays that are 852 by 480 match an ATSC format in the vertical dimension, but would have to significantly window-box to match the horizontal display. A display dimension of 1024 by 768 is a common classic computer display resolution, and does not match DTV in either dimension; it would have to crop, both letter- and pillar-box (possibly combined with cropping), or scaling. A display that is 1920 by 1080 would have to neither crop nor scale nor blank portions of the display, of course.
Consider Height and Width
Much is made of the vertical display resolution when involved in discussions of DTV.
Realize that the horizontal display width — the horizontal resolution — is the other key factor in determining the display size, and realize there are various DTV displays available that do not provide the full DTV width for the advertised vertical height. When looking at a 1080 display, for instance, consider confirming the width is 1920 pixels, and check for 1280 pixels width for a 720 pixel height display.
If the device does not offer the full width for the rated display height, then some manner of display clipping or scaling must obviously occur. Conversely, if the device has more than the rated width, you can obviously receive the rated width at the native resolution using vertical bars to the left and right; using a pillarbox display technique.
There are DTV devices on the market that might well imply HDTV capabilities, but that do not support the full display height of either 720 or 1080 rows, or the full width of 1280 or 1920 columns.
Tuners and Signals
The traditional M Format analog signal encoding used for TV broadcasting since the 1940s was defined by the National Television Standard Committee (NTSC). Many wags have subsequently translated NTSC as Never The Same Color or Never Twice the Same Color, in response to the difficulties with the display color reproduction differences within the system — NTSC was in operation for over a decade before broadcast color capabilities were retrofit into the signaling, and has never been known for its ability to consistently reproduce colors.
Digital TV signaling is encoded using one of various schemes defined by the Advanced Television Standard Committee (ATSC, and the obvious translation Always The Same Color), and provides both higher resolutions and far better color reproduction. There is no particular need to know the details of the different encoding schemes when considering the purchase, as all current commercial ATSC receivers receive and process all of the schemes.
Rather than the details of the formats, you will want and need to know the four basic resolutions (the format names, in the following table), those known as Standard Definition TV (SDTV), Enhanced Definition TV (EDTV) and the two High Definition TV (HDTV) resolutions; the 720 and 1080 formats. You will also want to know if the display is Progressive or Interlaced. These will help you choose the native display format(s).
| Format Name | Format Acronym | Horizontal Columns | Vertical Rows | Aspect Ratio | Scan Mode | Frame Rate |
|---|---|---|---|---|---|---|
| HDTV | 1080p | 1920 | 1080 | 16x9 | Progressive | 24 |
| 1080p | 1920 | 1080 | 16x9 | Progressive | 30 | |
| 1080i | 1920 | 1080 | 16x9 | Interlaced | 30 | |
| 720p | 1280 | 720 | 16x9 | Progressive | 24 | |
| 720p | 1280 | 720 | 16x9 | Progressive | 30 | |
| 720p | 1280 | 720 | 16x9 | Progressive | 60 | |
| EDTV | 480p | 704 | 480 | 16x9 | Progressive | 24 |
| 480p | 704 | 480 | 16x9 | Progressive | 30 | |
| 480p | 704 | 480 | 16x9 | Progressive | 60 | |
| 480p | 704 | 480 | 4x3 | Progressive | 24 | |
| 480p | 704 | 480 | 4x3 | Progressive | 30 | |
| 480p | 704 | 480 | 4x3 | Progressive | 60 | |
| 480p | 640 | 480 | 4x3 | Progressive | 24 | |
| 480p | 640 | 480 | 4x3 | Progressive | 30 | |
| 480p | 640 | 480 | 4x3 | Progressive | 60 | |
| SDTV | 480i | 704 | 480 | 16x9 | Interlaced | 30 |
| 480i | 704 | 480 | 4x3 | Interlaced | 30 | |
| 480i | 640 | 480 | 4x3 | Interlaced | 30 |
The four display formats cover the native display you see, and what conversions might be required. Do confirm that the display you choose will display one (or more) of the formats as the native format. Not all do, just to keep things interesting.
And do remember to confirm the width, and not just the advertised display height, if you seek to acquire a display with the full native DTV resolution(s).
Reception
NTSC and most analog communication signals do degrade somewhat more gracefully than ATSC, and you can generally watch an NTSC broadcast through substantial interference; through static or snow. With ATSC and digital communications signals, you will generally either have a reliable picture, a badly blocked or pixelated display in the fringe areas of broadcast reception, or no signal and no picture. Why do you need to know this? Upgrading from NTSC analog TV to ATSC digital TV can mean you will also need a better antenna.
DTV is available over some cable and satellite systems, and is also broadcast over the air (OTA) in many areas. (For localized information on OTA DTV reception and for recommendations on appropriate types of DTV antennae, the AntennaWeb.Org site can be quite useful.)
If you do choose to try OTA DTV, you will want a good UHF antenna, and potentially also a good VHF antenna in a few areas of the country. As with digital cellular telephone and with digital trunking radio communications systems, OTA DTV signals either receive and decode, or they don't — much more than classic analog TV, classic analog cellular telephone or analog radio communications, you will either receive a digital signal or you don't. Marginal DTV signals will pixelate (eg: random blocks or tears in the display; the digital version of static), and the audio signal suffers drop-outs. The result of a marginal, poor, corrupt or weak OTA DTV signal is often unwatchable; much more so than the static of a marginal analog TV signal.
If you want to test DTV OTA reception prior to a large(r) investment, PCI-bus-based ATSC receivers are available for under US$200, and external ATSC receivers are available for under US$400. The former allows you to receive ATSC broadcasts on your computer (with the appropriate software, usually packaged with the PCI controller), while the latter allows you to receive and display ATSC broadcasts on an HD or ED display, or even on a SD display. You can also use a tuner to record ATSC broadcasts (in SD format) on an SD VCR, as well.
Content and CableCARD?
If you plan to use cable or satellite as your source for HD content, you will want to look into CableCARD support in your DTV. This hardware support is coming on-line, and provides the mechanism (currently) intended to allow the maintenance of subscription information and for viewing of protected content. You may well require a set-top box (STB) for cable or satellite reception, in addition to the CableCARD support, too. (Do check with your local cable provider here, as CableCARD support among cable companies is far from universal. The FCC mandated its existence in DTV devices, but not its use. Thus the STB mess. The theory that the FCC was likely considering here was akin to the SIM cards found within the GSM telephone networks; where the subscription and services would follow the SIM card (or the CableCARD), and not the cellular handset (or set-top box). But CableCARD “isn't there yet.”)
As for potential CableCARD schemes, the GSM SIM-like mobility of the CableCARD is just the start. Imagine issuing your kids a CableCARD that locked out adult or extra-cost content, for instance. Or even a CableCARD that provided a limited number of hours of viewing. Kiosks or commercial services could update and authorize, or could provide you with gift CableCARDs, or with cards for specialized purposes. (Access into one or more DTV data carriers, for instance, or access into specialized feeds or services.) Theoretically, the CableCARD is a very powerful concept. But if the providers cannot or will not sort it out, then the CableCARD will remain an unused technological appendage, serving only as a slot that collects dust.
The Choice
Which to pick? That's up to you, your requirements, and particularly your budget, of course.
A home theater system might see a DLP projector or a (big) plasma, while a smaller room would see a mid-sized LCD. A kitchen would likely see an LCD panel due to its size, price, and portability.
If price is a central concern, you can't beat a CRT.
The sweet spot for (low) price and (large) size is presently arguably occupied by the DLP or other similar "MicroDisplay" technologies.
If cable is a consideration, you might want to look for a system offering a CableCARD, though this support is not widely integrated as of this writing.
The single and central consideration: HoffmanLabs would only recommend purchasing a DTV with a dedicated or preferably with a fully-integrated ATSC, or with a combination ATSC and NTSC tuner.
And remember, whatever you purchase will become quickly dated, as DTVs are progressing more akin to computers (prices continuously dropping and/or capabilities continuously improving, or both) than to the comparatively static TV technologies of old. Choose and buy what meets your requirements, and what you can reasonably afford, and then relax and enjoy your DTV. And do expect to replace it somewhat more frequently than you probably replaced your old analog CRT TV.