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This article was found on The Audio Critic Webzine.

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There’s no denying that LED-backlit LCD TVs are LCD TVs that contain LEDs as a source of backlighting instead of traditional CCFL bulbs. But when it comes to introducing the technology at the retail level, the issue can lend to a lot of customer confusion. For one, if you call it an LED-backlit LCD, the customers’ eyes will likely glaze over. But if you call it an LED TV, aren’t you misinforming him? After all, the only truly “LED” TVs on the market are ones like that 11″ Sony OLED beauty that was introduced a few years back. Right?

Some would say it’s all semantics, but judging from the industry debate, it’s clear that whether you agree with one side or the other, it’s an issue that requires addressing.

“LED TVs”
If features like slim form factor, energy savings, and better picture quality, can’t be achieved using traditional TFT LCD technologies, than how can we possibly use the same name? And if light source has nothing to do with naming a flat panel, why do we call a plasma a plasma?

Then again, the difference between TFT-LCDs with CCFL backlights and LCDs with LED backlights is significant enough that consumers need to understand the benefits. In this respect, you’re selling yourself short by selling these flat panels simply as LCDs.

According to Robert Gumiela, Director of Marketing for CE at Samsung Electronics of Canada Inc., there is a bevy of differences between LCD and “LED” that warrant dropping the LCD moniker.

“What has four wheels, a steering wheel, and an engine?” he asks, showing us a diagram of a golf cart, a tractor, and a Maserati. “It would be rather interesting playing eighteen holes using a Maserati, cruising the Autobahn on a tractor, or plowing fields with a golf cart. They share a commonality of being vehicles and providing transportation, but their differences outweigh their similarities.”

He moves on to his next example. This time, the photo depicts a calculator, a wristwatch, and a clock radio. “They are all true liquid crystal displays,” he says, “but it would be quite interesting using them to watch TSN in HD. What we know as an LCD TV is really a TFT-CCFL liquid crystal display device that combines a variety of technologies to product a high-definition video image.”

Analogies are great, but Gumiela cites eight points that he feels really bring his position home.

* LED is a solid state semi-conductor opposed to a CCFL which uses a fluorescent lamp to produce light;
* LED light is significantly faster in rise and decay time which results in better contrast ratios and better motion performance;
* The liquid crystal substrate is modified to account for faster LED response time. (Sure, there is a substrate that contains liquid crystals, but you have to have a thin film transistor layer to actually control them. And because LED performs differently, that TFT is different.);
* The LED light path uses a number of substrate elements (light plates, prisms) which is distinctly different to a conventional CCFL ;
* The LED colour gamut (typically 105% of HD colour gamut) is distinctly different to a conventional CCFL;
* LED panel substrates utilize enhanced polarization films;
* LED utilizes significantly less power than conventional CCFL;
* LED light technology contributes to a remarkably different mechanical or cosmetic design.

While Samsung is a big proponent on this front, the Korean manufacturer is not alone in its stance. Listen to any Bay Bloor Radio radio ad and you’ll note that the downtown Toronto retailer clearly distinguishes among plasma, LCD, and LED TVs.

According to Richard Bowden, the retailer’s Director of Sales, customers find it easier to understand the situation this way. “Category One: Plasma. Category 2: LCD (we explain the basics; the rear-mounted fluorescent tubes, etc.) Category Three: LED. (we explain the sub-categories of full array and edge lit).

“To clients,” he continues, “they seem to want to know which is the newest technology, which is most energy efficient, and of course which is the thinnest. At the end of the day, there is a lot of LCD, LED, ABC going around. Of course the most important thing is to reinforce that most premium brands are exiting the LCD label and moving to LED.”

However, Bowden does admit that the TVs are discussed as somewhere along the lines of the next-generation LCD TVs, which means the three-letters aren’t completely lost in translation.

To the counter-points noted in the opposite section, Gumiela muses: “I’m still trying to watch the hockey game on my LCD clock radio. I tried changing the back light, but to no avail.”

Samsung Canada’s Robert Gumiela poses proudly in front of a series of complex diagrams and calculations that he feels justify why LCD TVs with LED backlighting should be called LED TVs.

“LCD TVs”
Regardless of the lighting technology, and the technical modifications made to facilitate the advantages found in LED backlit LCD TVs, they’re still ultimately LCDs. We don’t use the lighting source to determine the moniker attached to a TV; we use the type of panel. Otherwise, CCFL models would be called CCFL LCD TVs.

If you tell a consumer he’s buying an LED TV, then he takes it home and presents it to his propeller-head friend as such, said friend will probably laugh hysterically at him for being duped by the retailer. Imagine that customer furiously rushing back into the store to yell at the sales guy who “misinformed” him about what he was buying.

Gumiela is right in that you can’t ride a tractor along the green during an 18-hole game, nor use a Maserati to transport farm equipment. But the modes of transport can be distinguished by more specific names: a golf vehicle, a farming vehicle, and a luxury vehicle, for example. Similarly, we have CCFL LCD, LED LCD, or even to a greater extent, full-array LED LCD, edge-lit LED LCD, and so forth.

Fred Breitner, Owner of Great Metropolitan Sound in Toronto, ON, likens the situation to the idea of the “borderless TV.” It’s named as such because the bezel extends to the very edge of the unit, thus making it look as if there’s no border. But when you actually turn the TV on to view video, it’s misleading, because there is indeed a border around the actual picture.

Andrew Thompson, Marketing Manager, CE, at Sharp Electronics of Canada Ltd., uses a different analogy: rear-projection TV. “If you look at the evolution of RPTV,” he explains, “there have been multiple new fundamental technologies introduced; there was CRT, microdisplay (LCD, LCOS, D-ILA), DLP, and now laser. But we haven’t changed how we refer to them; they are still RPTV.”

“LCDs are barely all the way through their development cycle,” he adds. “We cannot create a new category type of TV every time there is an advancement.”
To Gumiela’s eight points, Thompson counters his own.

* There are many solid state components in an LCD TV, not just the backlight;
* It’s a component that improves performance, just like a higher performing processor. We upgrade our processors every product cycle, and CPUs used now are many times more powerful and dynamic than ones used just several years ago, yet we don’t change the TV category;
* But it’s still a liquid crystal substrate, right?;
* These are the same types of components used in CCFL edge lit displays for PCs and laptops enabling light guidance and addressing uniformity issues inherent in edge-lit displays. Nothing new nor significantly unique about the technology;
* CCFL is capable of similar colour gamut coverage. Sharp, for example, used 4 and 5 wavelength CCFL backlights to reach similar numbers;
* There is a plethora of polarization film manufactures and flavours. Fundamentally these are not different for LED backlit displays;
* HCFL backlighting also offers a low power alternative to CCFL, yet we don’t see “HCFL TVs” advertised as a product category;
* Depends on the definition of “remarkably different”. Is the difference between one and two inches “remarkable” enough to justify a new display category?

Breitner says it’s the new name that confuses customers, not trying to explain the differences between LCD with LED backlighting and CCFL. In fact, he says Great Met sees at least one customer a day who’s looking for that new LED TV, and is dead set that he doesn’t want that old LCD stuff.

For his part, Breitner agrees with all of Gumiela’s claims, especially that there are tons of technical differences between the technologies. “But,” he shrugs, “they’re still LCD TVs. And there’s no reason to obfuscate this.

Christine Persaud

Marketnews

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As DVI and HDMI connections become more and more widely used, we are often asked: which is better, DVI (or HDMI) or component video? The answer, as it happens, is not cut-and-dried.

First, to clear away one element that can be confusing: DVI and HDMI are exactly the same as one another, image-quality-wise. The principal differences are that HDMI carries audio as well as video, and uses a different type of connector, but both use the same encoding scheme, and that’s why a DVI source can be connected to an HDMI monitor, or vice versa, with a DVI/HDMI cable, with no intervening converter box.

The upshot of this article–in case you’re not inclined to read all the details–is that it’s very hard to predict whether a digital DVI or HDMI connection will produce a better or worse image than an analog component video connection. There will often be significant differences between the digital and the analog signals, but those differences are not inherent in the connection type and instead depend upon the characteristics of the source device (e.g., your DVD player) and the display device (e.g., your TV set). Why that is, however, requires a bit more discussion.

What are DVI, HDMI and Component Video?

DVI/HDMI and Component Video are all video standards which support a variety of resolutions, but which deliver the signal from the source to the display in very different ways. The principal important difference is that DVI/HDMI deliver the signal in a digital format, much the same way that a file is delivered from one computer to another along a network, while Component Video is an analog format, delivering the signal not as a bitstream, but as a set of continuously varying voltages representing (albeit indirectly, as we’ll get to in a moment) the red, green and blue components of the signal.

Both DVI/HDMI and Component Video deliver signals as discrete red, green, and blue color components, together with sync information which allows the display to determine when a new line, or a new frame, begins. The DVI/HDMI standard delivers these along three data channels in a format called T.M.D.S., which stands for “Transmission Minimized Differential Signaling.” Big words aside, the T.M.D.S. format basically involves a blue channel to which horizontal and vertical sync are added, and separate green and red channels.

Component Video is delivered, similarly, with the color information split up three ways. However, component video uses a “color-difference” type signal, which consists of Luminance (the “Y”, or “green,” channel, representing the total brightness of the image), Red Minus Luminance (the “Pr,” or “Red,” channel), and Blue Minus Luminance (the “Pb,” or “Blue,” channel). The sync pulses for both horizontal and vertical are delivered on the Y channel. The display calculates the values of red, green and blue from the Y, Pb, and Pr signals.

Both signal types, then, are fundamentally quite similar; they break up the image in similar ways, and deliver the same type of information to the display, albeit in different forms. How they differ, as we’ll see, will depend to a great extent upon the particular characteristics of the source and display devices, and can depend upon cabling as well.

Isn’t Digital Just Better?

It is often supposed by writers on this subject that “digital is better.” Digital signal transfer, it is assumed, is error-free, while analog signals are always subject to some amount of degradation and information loss. There is an element of truth to this argument, but it tends to fly in the face of real-world considerations. First, there is no reason why any perceptible degradation of an analog component video signal should occur even over rather substantial distances; the maximum runs in home theater installations do not present a challenge for analog cabling built to professional standards. Second, it is a flawed assumption to suppose that digital signal handling is always error-free. DVI and HDMI signals aren’t subject to error correction; once information is lost, it’s lost for good. That is not a consideration with well-made cable over short distances, but can easily become a factor at distance.

So What Does Determine Image Quality?

Video doesn’t just translate directly from source material to displays, for a variety of reasons. Very few displays operate at the native resolutions of common source material, so when you’re viewing material in 480p, 720p, or 1080i, there is, of necessity, some scaling going on. Meanwhile, the signals representing colors have to be accurately rendered, which is dependent on black level and “delta,” the relationship between signal level and actual as-rendered color level. Original signal formats don’t correspond well to display hardware; for example, DVD recordings have 480 lines, but non-square pixels. What all of this means is that there is signal processing to go on along the signal chain.

The argument often made for the DVI or HDMI signal formats is the “pure digital” argument–that by taking a digital recording, such as a DVD or a digital satellite signal, and rendering it straight into digital form as a DVI or HDMI signal, and then delivering that digital signal straight to the display, there is a sort of a perfect no-loss-and-no-alteration-of-information signal chain. If the display itself is a native digital display (e.g. an LCD or Plasma display), the argument goes, the signal never has to undergo digital-to-analog conversion and therefore is less altered along the way.

That might be true, were it not for the fact that digital signals are encoded in different ways and have to be converted, and that these signals have to be scaled and processed to be displayed. Consequently, there are always conversions going on, and these conversions aren’t always easy going. “Digital to digital” conversion is no more a guarantee of signal quality than “digital to analog,” and in practice may be substantially worse. Whether it’s better or worse will depend upon the circuitry involved–and that is something which isn’t usually practical to figure out. As a general rule, with consumer equipment, one simply doesn’t know how signals are processed, and one doesn’t know how that processing varies by input. Analog and digital inputs must either be scaled through separate circuits, or one must be converted to the other to use the same scaler. How is that done? In general, you won’t find an answer to that anywhere in your instruction manual, and even if you did, it’d be hard to judge which is the better scaler without viewing the actual video output. It’s fair to say, in general, that even in very high-end consumer gear, the quality of circuits for signal processing and scaling is quite variable.

Additionally, it’s not uncommon to find that the display characteristics of different inputs have been set up differently. Black level, for example, may vary considerably from the digital to the analog inputs, and depending on how sophisticated your setup options on your display are, that may not be an easy thing to recalibrate.

The Role of Cable and Connection Quality

Cable quality, in general, should not be a significant factor in the DVI/HDMI versus Component Video comparison, as long as the cables in question are of high quality. There are, however, ways in which cable quality issues can come into play.

Analog component video is an extremely robust signal type; we have had our customers run analog component, without any need for boosters, relays or other special equipment, up to 200 feet without any signal quality issues at all. However, at long lengths, cable quality can be a consideration–in particular, impedance needs to be strictly controlled to a tight tolerance (ideally, 75 +/- 1.5 ohms) to prevent problems with signal reflection which can cause ghosting or ringing.

DVI and HDMI, unfortunately, are not so robust. The problem here is the same as the virtue of analog component: tight control over impedance. When the professional video industry went to digital signals, it settled upon a standard–SDI, serial digital video–which was designed to be run in coaxial cables, where impedance can be controlled very tightly, and consequently, uncompressed, full-blown HD signals can be run hundreds of feet with no loss of information in SDI. For reasons known only to the designers of the DVI and HDMI standards, this very sound design principle was ignored; instead of coaxial cable, the DVI and HDMI signals are run balanced, through twisted-pair cable. The best twisted pair cables control impedance to about +/- 10%. When a digital signal is run through a cable, the edges of the bits (represented by sudden transitions in voltage) round off, and the rounding increases dramatically with distance. Meanwhile, poor control over impedance results in signal reflections–portions of the signal bounce off of the display end of the line, propagate back down the cable, and return, interfering with later information in the same bitstream. At some point, the data become unrecoverable, and with no error correction available, there’s no way to restore the lost information.

DVI and HDMI connections, for this reason, are subject to the “digital cliff” phenomenon. Up to some length, a DVI or HDMI cable will perform just fine; the rounding and reflections will not compromise the ability of the display device to reconstruct the original bitstream, and no information will be lost. As we make the cable longer and longer, the difficulty of reconstructing the bitstream increases. At some point, unrecoverable bit errors start to occur; these are colloquially described in the home theater community as “sparklies,” because the bit errors manifest themselves as pixel dropouts which make the image sparkle. If we make the cable just a bit longer, so much information is lost that the display becomes unable to reconstitute enough information to even render an image; the bitstream has fallen off the digital cliff, so called because of the abruptness of the failure. A cable design that works perfectly at 20 feet may get “sparkly” at 25, and stop working entirely at 30.

In practice, it’s very hard to say when a DVI or HDMI signal will fail. We have found well-made DVI cables to be quite reliable up to 50 feet, but HDMI cable, with its smaller profile, is a bit more of a puzzle. Because the ability to reconstitute the bitstream varies depending on the quality of the circuitry in the source and display devices, it’s not uncommon for a cable to work fine at 30, 40, or 50 feet on one source/display combination, and not work at all on another.

The Upshot: It Depends

So, which is better, DVI or component? HDMI or component? The answer–unsatisfying, perhaps, but true–is that it depends. It depends upon your source and display devices, and there’s no good way, in principle, to say in advance whether the digital or the analog connection will render a better picture. You may even find, say, that your DVD player looks better through its DVI or HDMI output, while your satellite or cable box looks better through its component output, on the same display. In this case, there’s no real substitute for simply plugging it in and giving it a try both ways.

This article was found on the Ecoustics forum.

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