Secrets of Home Theater and High Fidelity
Volume 1, Number 1, 1994
Section 1. Televisions (Revised January, 2001)
Index for Televisions:
Vacuum tubes and television (black & white as well as color) were patented in the first decade of the twentieth century, but the initial public television broadcast was not until 1939. Since that time, TV has become an extremely popular form of home entertainment, most of us spending many hours each week in front of the "tube". Programming has changed dramatically over the years, and I remember in the early 1960s when a talk show host had to interrupt someone in the audience who mentioned "toilet paper". "We can't talk about that on the air", the host admonished. Now, of course, there are no limits (unfortunately!) to what we can tune in to, if we subscribe to particular cable channels. We sit on the threshold of the information highway where we will be able to utilize television to educate our families, and perform many chores such as shopping and banking, at home. Naturally, entertainment will always be there, and with cable systems ready to launch hundreds of channels in our faces, we will have to make a concerted effort not to become that proverbial "couch potato". In spite of such caveats, most of us enjoy TV quite a bit, and with so much programming available, there is usually something worth watching at most any time of the day or night.
When television was invented, certain decisions had to be made. One of these was how sharp to make the picture (available technology and cost effectiveness). The first picture tubes were quite small, and the engineers figured that the image should be sharp enough so that viewers would not notice any loss of detail with the picture of that small size, and with the viewer sitting an average distance from the TV set.
Although we see the image as occupying the full face of the picture tube, it is actually painted across the screen in constantly moving horizontal brush strokes, called "scanning lines". At the rear of the picture tube is an electron gun, which is basically a heated wire filament. The heat causes electrons to form a "cloud" around the filament. A high positive voltage accelerates the negatively charged electrons from the filament in a thin beam toward the face of the TV screen where they strike a phosphor coating. The phosphors glow where the electrons strike. The image is formed by scanning the electron beam in 525 horizontal lines (625 in Europe) across the screen, with scanning line 1 at the top of the screen, and scanning line 525 at the bottom. (In reality, some of the 525 lines are lost during the time when the electron beam moves from the bottom of the screen back up to the top to begin the next scanning sequence, so, the actual number of scanning lines that end up being shown on the screen is 483, but for the sake of consistency with television literature, we will continue the discussion as if there were 525 lines.) Where the scene is dark, the electron beam is weak, so the phosphors do not glow very much. Where the scene is bright, the electron beam is intense, so the phosphors glow brightly. The scanning of the beam across the face of the picture tube is coordinated with scanning of the original scene (people, landscape, etc.) by a sensor in the television camera, and as the scanning lines become bright, dark, and intensities in between, the image is formed. The "resolution" of a TV image is the ability to distinguish alternating light and dark lines that are close together. If the lines were too close together (beyond the resolution limits), the lines merge into gray. The "vertical resolution" of NTSC TV is the 525 HORIZONTAL scanning lines. That does not change. However, the "horizontal resolution" (number of VERTICAL lines) changes with the source. The horizontal resolution of VHS tape is about 240 lines, broadcast TV is 330 lines, laserdisc is 420 lines, and DVD is 480 lines.
Lines 1 - 525 are not scanned in sequence, but rather, every other line is scanned. In the first 1/60th of a second, lines 1, 3, 5, 7, etc. (through line 525) are scanned and shown, then lines 2, 4, 6, 8, etc. (through line 524) are scanned and shown in the next 1/60th of a second. This method of display is called interlacing and is done so that the eye will not see any flicker (your brain interprets 60 flashes of image per second as continuous). Thus, an entire single image (frame) is shown in two interlaced scans (fields) of 1/60th plus 1/60th of a second, which equals 1/30th. During this 1/30th of a second, the image is not moving, but is like a snapshot picture.
Normally, one frame is shown in two fields (two interlaced scans) and, thus, for live or videotaped broadcasts, we see 30 frames (60 fields) per second, giving the illusion of movement. Motion pictures on film are made at 24 snapshots (frames) per second. If we were to show the 24 frames of film per second on TV in the usual two fields per frame, we would end up with only 48 fields per second, which would result in 12 fields per second (6 frames) being left over from the 60 fields per second (30 frames) of TV scanning. Fitting these 24 frames of film per second into television which is displayed at 30 frames per second on the TV monitor is tricky. The problem is solved by showing every other movie frame in three fields rather than two (the third field is usually a repeat of the second field). Thus, movie frame 1 would be shown in two fields, movie frame 2 would be shown in three fields, movie frame 3 would be shown in two fields, movie frame 4 in three fields, and so on. This adds up to having the 24 frames per second of the film being spread out over 30 frames per second of the television.
Since television has to be divided into 60 fields per second (2 fields per frame) to eliminate visible flicker, you might wonder why you don't see flicker at the theater with 24 frames per second. Flicker is eliminated by a spinning plate in the projector which breaks each frame of film into two flashes on the screen.
Improved Definition Television (IDTV) is a process applicable in our current televisions, but is available in very few models. The process converts the interlaced image into a non-interlaced one. The initial field (lines 1,3,5, etc.) is stored in computer memory but not shown. Then, the second field (lines 2,4,6, etc.) is added to the first field, and all the scanning lines which make up the complete frame (lines 1,2,3,4,5,6, etc.) are shown at the same time. The effect is one of reducing the visibility of distinct scanning lines when you view the image. However, the process requires very fast computer memory, and "motion artifacts" can be perceived because currently available memory chips are just not quite fast enough (although they are improving). This will show up when the camera is panned from side to side, giving stationary objects in the scene a smeared effect as the camera passes them by. (Look for the effect by watching the spectators at a sporting event when the camera follows the atheletes.) Also, the image may not be as sharp as the regular interlaced image. However, if your dealer has a TV with IDTV capability, you should compare it with regular television images, because you might prefer the soft velvety appearance that it typically has.
Line doublers are very high tech, very expensive, and very impressive electronic devices that double the number of scanning lines (principal manufacturer is Faroudja). They work by examining the initial field (lines 1,3,5, etc.), and then generating, by computer technology, lines of information in between, based on what is contained in the lines above and below. In other words, a new line will be generated between lines 1 and 3, based on what is in those lines, a new line between 3 and 5 based on those lines, and so on. Then the field, made up of the original scanning lines and the computer generated lines, is shown for 1/60th of a second. The second field (lines 2,4,6, etc.) is treated the same way and shown in the next 1/60th of a second. Both IDTV and line doubler technology are considered to be non-interlaced. However, while IDTV adds both fields together and shows them at the same time as a single frame, the line doubler shows each field separately, with computer generated lines added to each field.
Line doubling is an estimation technique, but works very well. To incorporate the most sophisticated line doubling technology into your home theater, you will need a front projection TV system, called a "Data Grade Projector", with RGB (Red, Green, Blue) as well as Sync (Synchronization) inputs, and capable of scanning at a frequency of 31.5 kHz. This is double the scanning frequency of standard NTSC TV (15.75 kHz - which is the product of 30 frames per second multiplied by 525 lines per frame). Some of these projectors are adaptable to the future HDTV (see below), which also uses a high scanning frequency - 4 times the basic NTSC frequency (check with your dealer about upgradability to HDTV). A data grade projector will cost about $10,000 by itself, with the line doubler adding thousands more, so ask plenty of questions and plan for nice long demonstrations if you consider purchasing this type of equipment.
Line quadrupling is now available as an accessory for data grade projectors having 63 kHz scanning frequency capability (4 x the NTSC frequency). The image is spectacular with line quadruplers because no scanning lines are visible, even up close. The cost is high at this point (over $20,000), but if the technology is condensed into a few massed produced computer chips, this dazzling image improvement could become available on consumer NTSC TVs. Lastly, "Interpolators" are available, which determine the optimum scanning frequency for a particular TV, and apply that scanning frequency rather than using doubling or quadrupling. In other words, the scanning frequency may be somewhere in between. Snell and Wilcox make superb interpolators, but the cost is very high ($28,000). They produce beautiful video images, especially with top of the line projectors such as those made by Vidikron. HDTVs have line doubling built-in, and they only cost $7,000, which makes them economical compared to some of the stand alone line doublers.
All televisions are subject to a problem called "dot crawl". This shows up along horizontal or diagonal edges of objects that have contrasting colors (for example, yellow adjacent to blue), and looks like a moving stairway (escalator). It is caused by the imperfect ability of the comb filter in the TV (or video player) to separate the color signal from the luminance (brightness) because the frequencies overlap. The amount of dot crawl varies with the quality of the TV, but also those units with special image processing features that allow you to enlarge the picture to fill the screen (in "widescreen" TVs; see below) or to magnify a part of the image you want to see in more detail, may be particularly prone to exaggerated dot crawl. Therefore, look for this artifact when choosing a television, especially those with sophisticated arrays of image manipulating capabilities.
High Definition Television (HDTV) began broadcasting in the United States in 1998. It uses interlacing in its best mode (called 1080i), and non-interlacing, called progressive scanning, in its next best mode (called 740p). Progressive scanning means that all the lines are scanned in sequence rather than all the odd lines followed by all the even lines. (High quality computer monitors already do this.) 1080i means that there are 1080 horizontal scanning lines, split up into two sets of 540 alternating lines each, and the two sets are displayed one after the other ("interlaced"). Lines 1,3,5, etc. are in one set, and lines 2,4,6, etc. are in the other set.
HDTVs are shaped in the 16:9 aspect ratio ("Widescreen") and can scan at 24 or 30 frames per second, alleviating the problem of fitting 24 movie frames into 30 television frames, as just described. The US version of HDTV is all digital, while HDTV that already exists in Japan and Europe started out as analog and is converting to digital. Digital television transmission results in less "ghosts" and other interference that mars current analog transmission. All HDTVs are digital TVs (DTV), but not all digital televsions are HDTVs. There are many resolutions which can be used in digital TV transmissions, including 480 which is the same resolution as our current NTSC TVs. An additional feature of HDTVs is that they can line double, which means that our NTSC programs will look much better on an HDTV than on a standard TV. So, it is worthwhile to get an HDTV now, even though actual HDTV programming is sparse.
Many of the HDTVs available now can handle 1080i but not 720p. However, it is possible we may not see 720p programming for quite some time anyway. Projection HDTVs need 9" CRTs to display 1080i. Projection TVs with 7" CRTs or smaller cannot display the full 1080i resolution.
Purchasing a television with home theater in mind these days is not an easy decision. There are three basic types of televisions to choose from: Direct View, Front Projection, and Rear Projection. Direct view is the type we are all most familiar with. It is your basic garden variety television where you are looking directly at the picture tube. Front projection TVs are the type you are likely to find in bars which cater to people who want to watch sporting events while they eat and drink. The projection system is usually mounted on the ceiling, and it contains three small but very intense picture tubes, one each for red, green, and blue. These three colors, when mixed together in the right combinations, give the viewer all colors. For example, red and green, when projected on the same area of the screen, are sensed by the brain as yellow. The three color tubes are aligned to show their images on a screen mounted on the wall, one image on top of the other. The combination of the red, green, and blue images form the full color picture.
There are some front and rear projection designs which use liquid crystal display (LCD) technology rather than standard picture tubes, and which provide excellent images at reasonable prices. If you like the idea of front or rear projection, these models should be considered.
Rear projection TVs are the kind we usually have at home, calling them "Big Screen TVs". They also have the three color tubes, mounted in the base of the TV, projecting their images towards the rear. The three color images then bounce off a large mirror and are reflected frontwards where they project on the back side of a plastic screen to form the final converged picture. Thus, for a front projection TV, the image is projected onto the front of the screen, and you view it from the front. For a rear projection TV, the image is projected onto the rear of the screen, but you still view it from the front.
Let's talk now about the advantages and disadvantages of all three types of televisions. The direct view TV has the sharpest image (except for the very best front projectors, which, including the screen, can cost about $80,000). This is partly because it uses one picture tube. Perfect alignment of the images of the three color tubes in the front and rear projection TVs is impossible, except under certain situations (see below), because they are projecting through separate lenses from different angles. So, in one corner of the screen, the three colors will not be aligned. It isn't that big a deal, though; you just choose the corner that is least important to you when you adjust the alignment. For me, this is the bottom left corner. Secondly, the direct view TV is sharper because you are looking directly at the picture tube. In projection TVs, the picture tube images are passed through projection lenses, and the image is formed on a wall or plastic screen which scatters the light. This light scattering reduces sharpness. In essence, then, you are looking at a projected image from the picture tube, rather than the picture tube itself. Direct view TVs can be viewed in bright rooms, while projection TVs must have the room darkened, by closing the curtains or blinds. The room containing the front projection TV must be darker than for the rear projection TV because the image is projected onto the front of the screen where it can mix with stray light from windows. With a rear projection TV, the image is projected onto the backside of the screen, and stray light from a window hitting the front of the screen does not affect the image as much.
If direct view TVs could be made in any size, without a huge back end, there would be no question that this is the type to purchase. However, the largest direct view set made at this point is 40 inches (diagonal), while projection TVs can have images up to 8 feet or so. You will have to decide which is more important to you: sharpness or size. The 35 inch direct view TV is very affordable, and would make the best choice if sharpness is your most important consideration. Rear projection sets are in a similar price range, so as long as you are purchasing the TV for home theater, price won't be the factor which determines whether you buy direct view or rear projection. The front projection TV is complicated and generally quite expensive when you take into account that it does not come with a tuner or sound system, so even if you just want to watch the evening news, you have to turn on the complete hi-fi audio system, as well as a tuner (the one which is present in your VCR will do). However, if you want to go the whole nine yards, a front projection system is very nice because the projector can be mounted on the ceiling, out of the way, the screen can be retracted when not in use, the projected image can be huge, and such ancillary equipment as line doublers, quadruplers, or interpolators can be added. A few models offer projection of the three color images through one lens, so the alignment problem mentioned above is eliminated. Also, there are some projection TVs that use electronic alignment which changes the position of the image projected on various places of the screen to compensate for the differing angles of each projection lens. For the majority of us, direct view or rear projection is the most cost effective plan.
If you decide to go with the rear projection set, the 50 inch (diagonal) models are a good place to begin looking. If you want something smaller than this, then you should probably get the direct view rather than the rear projection, because they are about the same size, and direct view is sharper. There are rear projection models which are very large (up to 10 feet diagonal), but room size considerations start to come into play when boxes this big have to fit into the decor.
With High Definition Television (HDTV) upon us, you have another factor to consider: Aspect Ratio. This is defined as the ratio of the width of the TV screen to the height. For example the standard televisions we use at present have an aspect ratio of 1.35:1 (sometimes called 4:3). That is, the TV screen is 1.35 times as wide as it is high. The aspect ratio of HDTV is 1.78:1 (often referred to as 16:9), which is slightly more rectangular. The reason this is occurring is because we are so used to seeing long rectangular images at the theater, and manufacturers feel that the new technology should include a facelift, namely a more rectangular shape.
Films at the theater vary in aspect ratio. In the United States, they are usually either 1.85:1 or 2.35:1. The former is the more common, basically because it is less expensive. The process involves shooting the motion picture on standard 35mm film, at an aspect ratio of 1.33:1 (this is called being filmed "spherical" or "flat") and then, when it is shown at the theater, small metal plates in the projector crop the top and bottom of the image so that it is projected on the screen at 1.85:1. This is called "Soft Matting" (not standardized terminology, but it is descriptive and serves a useful purpose here). Occasionally, the film is shot spherically on 35mm film and then cropped to 2.35:1. Such was the case for "Terminator 2", "Apollo 13", and many others. Of course, when the director is shooting the picture, there are marks in the camera viewfinder as to what will be seen at the theater and what will be cropped. Sometimes, when the motion picture is finally shown on television, the parts of the image that were cropped at the theater are allowed to be seen, in order that the entire TV screen will be filled. For example, "Back to the Future 2" was shown at the theater soft matted at 1.85:1, but when broadcast on TV, it was shown without the soft matting.You might remember an occasional film on TV where you can see the microphone at the top, and you wonder, "How did they miss seeing that when they made the movie?" Well, they did see it, but it was cropped at the theater.
Movies filmed at 2.35:1 (it is more like 2.40:1, but most literature states it at 2.35:1) aspect ratio (CinemaScope ® and Panavision ®) are usually made by squeezing the long rectangular image sideways onto the standard 35mm film space using what is called an "anamorphic lens". At the theater, another anamorphic lens on the front of the projector unsqueezes the image so that it is appears normal when shown on the screen. These high aspect ratio anamorphic movies were begun in the early 1950s because people were staying home to watch television instead of going to the theater. Color and stereophonic sound helped make this a great success. For additional information on anamorphic photography, see the diagram in the article by Panavision [click here].
Originally, television was designed with an aspect ratio of 1.35:1 (4:3) so that movies, which, at the time, had virtually the same ratio, could be shown without cropping any of the picture. However, when CinemaScope movies were shown on TV, only about half the rectangular image could be shown, in order to fill the TV screen. This is called "Pan and Scan". It had to be done this way because, unlike the soft matting technique described above, there was no image at the top and bottom of the film to add back in when it was shown on TV. About 20% of theater movies are filmed anamorphically at 2.35:1, and the rest are filmed spherically and shown (mostly) at 1.85:1. HDTV, with its aspect ratio of 1.78:1 (16:9) does not match either of these formats, but engineering limitations dictated that this would be as high an aspect ratio that could be designed into the HDTV picture tubes.
The rectangular shaped images we see at theaters are called "widescreen" or "letterbox", as most movies are released nowadays in the original high aspect ratio on laser disc, DVD (Digital Video Disc or Digital Versatile Disc), a few on video tape, and some on cable TV. There is a great deal of interest in seeing films in their original widescreen aspect ratio, as shown at the theater, and Turner Classic Movies, as well as American Movie Classics cable channels routinely show them. The interesting thing is that widescreen movies started long before "The Robe" in the early 1950s. In fact, Hollywood was experimenting with them in the 1920s, and 1930s. One of John Wayne's first movies, "The Big Trail", was released in 1930, and in 70mm. Unfortunately, the stock market crashed in 1929, and theaters could not afford to show it. So, widescreen films had to wait until TV was keeping viewers at home before they would emerge en masse.
With a standard 4:3 television, widescreen movies leave blank space at the top and bottom of the screen. This is the only way to fit the rectangular widescreen image onto the more square-like 4:3 TV screen. Although some people get the feeling they are being cheated when they see a widescreen movie on TV, with so much blank space, it is really just a matter of how the movie was composed when it was filmed. If you compare a closeup scene in a widescreen movie with one filmed at 4:3 aspect ratio, you will find that the director usually moves the camera back farther from the subject in a widescreen film, in order to maintain a similar field of view height. In particular, people will often be filmed from just above the head to below the shoulders in closeups, regardless of the aspect ratio. Other than closeups, there is usually a bit more on the sides and a bit less at the top and bottom in a widescreen scene vs. a similar scene from a movie filmed at 4:3. When CinemaScope came out in 1953, the first few movies were filmed in the widescreen 2.35:1 format and also in the conventional 4:3 format just in case the movie audiences didn't like widescreen. Note the rare comparison of the same movie scene ("Demetrius and the Gladiators") filmed in CinemaScope (photo on the left) as well as standard 4:3 (photo on the right). The studio had to do different takes with the two different cameras.
High aspect ratio (2.35:1) movies do appear a bit odd (blank areas at the top and bottom of the TV screen) when seen on TV in the original ratio, probably because they were filmed for viewing on large theater screens. For example, "Ben Hur" is available at its almost 3:1 aspect ratio on home video. When compared to an old movie, like "The Sea Hawk", which was filmed at 1.33:1, "Ben Hur" can have a strange effect when the image is the same width but smaller height as the old movie. "The Sea Hawk" and "Ben Hur" are two of my favorite movies, and when I saw "Ben Hur" for the first time, in a Cinerama theater, it was breathtaking. I watch it at home with my feet practically resting on the base of the TV, because the widescreen image is so small. Two other examples of an old movie vs. a Panavision movie on a TV at the same width can be seen by clicking here to view a frame from "Sands of Iwojima" next to a frame from "The Longest Day". When a film that was made anamorphically and shown in letterbox form at the theater, such as "The Untouchables", then is shown on broadcast TV, it is usually modified to fit your TV screen, called "Pan & Scan" (P&S). Some people don't like the widescreen versions at home for one reason or another. However, the letterbox versions are the only way to see everything that the director intended. HDTV will alleviate the Pan & Scan problem, because they are 16:9 in shape. Widescreen movies will be shown at full width, while the 4:3 images will occupy the center of the screen. (All screen shots copyright respective studios.) For those consumers who hate widescreen movies, preferring the P&S, even if it means missing some of the picture, many new DVD players will let you enlarge the image so just the center part of the movie is seen, filling the TV screen.
There are several 16:9 NTSC TVs on the market, but they are not designed to receive HDTV, so you need to be careful when shopping for that new television. If you want HDTV, make sure that is what you are getting. Just because it is 16:9 does not mean it is HDTV. These NTSC 16:9 TVs receive standard broadcast signals (NTSC stands for National Television Systems Committee), with the standard 525 scanning lines (remember, only 483 lines are actually shown), and you can adjust the image to fit the screen shape. The 625 scanning lines for Europe is called PAL. If you want to watch a standard 4:3 image, it is formed in the center of the rectangular screen, and there is some blank space at the sides. You can zoom the 4:3 image to fill the screen, giving it a movie theater appearance, but a portion of the image is cropped off the top and bottom. Some people like this effect, and it is a matter of preference. If you plan to watch a lot of letterboxed movies, and want a low profile TV, this might be a choice to consider. The regular 4:3 TV image will be of a satisfactory size, and the letterbox movie will be nice and big (wide), the way it is supposed to be, without much blank area at the top and bottom.
Many DVD movies are stored on the disc in anamorphic format. This means the image occupies nearly the full height of the screen, but is squeezed side-to-side. When unsqueezed by the image expansion feature on 16:9 TVs, the picture nearly fills the screen instead of having large blank bars at the top and bottom. Irrespective of how the film is stored on the DVD, the movie may or may not have been filmed with anamorphic lenses. You can tell if it has by looking at out of focus lights behind the actors in night scenes when the lens apertures are large. If the lights appear as vertical ovals, then the movie was filmed anamorphically. An example of this is shown on the right, which is a screen shot from "The Postman".
To complicate matters even more, there is a third choice in aspect ratios for televisions available. This is the 16:10.7 aspect ratio TV. It is available in only a few models (e.g., Pioneer), but it is a very interesting television. It turns out that TV sets incorporate what is called "overscanning". This means that part of the image lies outside the viewing area of the TV screen. In a way, it is like matting your photos in a frame by overlaying the outside edges of the photo with the cardboard matte. This hides any rough edges. Overscanning accomplishes the same thing, hiding the rough edges of the broadcast signal plus a little extra just for good measure. These rough edges are caused when the electron beam, having scanned a line, returns to the left edge of the screen ("blanked", i.e., not visible during this time), and then begins another scanning line back across the screen. It takes a small amount of time for the beam to settle down, and something called "ringing" occurs. This results in a distortion of the image along the edges. Depending on the quality of the TV, the amount of overscanning can be up to about 8% so that this ringing will not be visible. The 16:10.7 aspect ratio Pioneer TV has less overscanning than the average TV, so a little more picture is visible on the sides of this rather unique television, and you might want to check one out, comparing side by side the images with those on a conventional set. For widescreen movie fanatics, some of the new DVD players will let you "zoom" the image, making it larger or smaller. In the case of a widescreen movie, you can reduce the image size a little, and this brings the overscanned areas on the right and left sides in so you can see them.
The distance from your television to where you will be sitting is a matter of several factors: the size of your room, where the rest of the furniture is arranged, and what is comfortable to your eyes. However, for those of you who like formulas, the Society of Motion Picture and Television Engineers (SMPTE) recommends that the screen should be of a size that you will see 30 degrees of viewing angle side to side from where you are sitting. If you really want to adhere to this, it means calculating either the size of the TV if you know how far away you will be sitting, or calculating the viewing distance if you know how big your TV screen is. The mathematics are easy. If we say that the horizontal (not diagonal) measurement of your television is "X", and the distance from your television to your seat is "Y", then the following formulas can be used to calculate the proper dimension for either one of these measurements: X = Y/1.8664 and Y = 1.8664 X. So, for example, if you are purchasing a television, and the distance from your seat to where you will be placing the TV is 6 feet, then you solve the equation for X. X = 6/1.8664 = 3.21 feet or 38.6 inches. Take a ruler with you to the electronics store and measure the horizontal width of the sets you are choosing from. If you have already purchased a television, then you need to calculate the proper viewing distance. If, for example, you have a television that is 4 feet wide, then you solve the equation for Y. Y = 1.8664 times 4 = 7.5 feet. In practice, using the above formula results in a viewing distance that may be too close for many viewers. A more reasonable number can be calculated using the principle of sitting back about 3 - 5 times the width of the TV. If that does not satisfy you, then just sit where you darn well please.
When you shop for the television, each set is marked with its diagonal size (the diagonal measurement is always larger than the horizontal, so using this number is more impressive). Actually, you don't need to be so exact. Comfort level is the rule, not mathematical formulas, but the formulas are there if you want to use them. If you have never owned a big screen TV, you may think that the ones you shop for are too large. However, you will be surprised at how fast you adapt to the large picture once you have it at home for a few days. When watching letterboxed movies in particular, larger screens are necessary for the best visual effect. Therefore, you will probably be more satisfied in the long run if you purchase the largest set you can fit into your viewing room.
Let's say that you have decided on about a 50 inch rear projection TV. Look in several stores. A good dealer will meet a competitor's price, so if you have decided on the model, find the lowest price, and you will be able to get it at the store you prefer to buy it from. Sit down on a couch or chair in front of the TV, and ask to handle the remote control. Is it comfortable to hold? Can you easily read the names of the functions written under the buttons? (Some have a button for illuminating the entire faceplate, which is great in a dark room.) Ask for a run-through on all the controls. Besides the usual channel selector and volume control, there will usually be buttons for controlling brightness, color level, tint, and sharpness. Tone controls (treble and bass) may be present. Other buttons to look for include a mute (when the telephone rings), programmable channels (this allows you to eliminate channels you are not interested in, so that when you press the channel up or down button, only the channels you have selected will appear), and input selector (this allows you to select a VCR or laser disc connected to the television). Picture In Picture (PIP) and Picture Outside Picture (POP) are found on many sets. This allows you to see two channels at once, and is great for checking the channel program guide while continuing to watch your current program. This requires two tuners, and some TVs have both tuners built in, while others require you to use an outside tuner for the additional picture. The VCR serves this purpose, but the VCR must be turned on to do this. If you want this feature, ask if the TV has two tuners.
Input jacks (sockets) are very important. Even if you are not going to build a complete home theater (with surround sound), most of us have at least a VCR, and the TV has to have separate video and audio jacks to connect it for the best picture and sound (it is possible to go through the antenna input, but this is not a good idea). Let's assume you will be using the TV in a home theater. The jacks should include at least one set of video input/audio left and right inputs, one (preferably two) S-Video input, and one set of video output/audio left and right outputs. Usually they are on the back of the TV, but occasionally one set of inputs is on the front, which is useful if you have a camcorder, and you might want to have this if you shoot home videos. These front jacks come in handy when viewing or transferring (editing) the video material from your camera tape to a permanent video album tape. If you use a Hi-8 or Super-VHS camcorder, then you should look for a S-Video input jack on the front of the TV. These are merely for convenience however. If the TV you really want does not happen to have front jacks, it is simply a matter of reaching behind the TV to connect cables when viewing or editing home video tapes from the camcorder.
With DVD, you should always use the S-Video connection, because the colors are stored in separated form (component video) on the DVD. That is, there are three signals: one for Y (luminance or brightness), and two for color, R-Y and B-Y. These are combined into Y and C for S-Video (two signals) in the DVD player. If the luminance and color are combined into one signal, it is called composite video. Separating the Y from the C in composite video to produce S-Video causes dot crawl, because the frequencies for Y and C overlap. No dot crawl will be seen using the S-Video output from a DVD player, because a comb filter is not necessary. The luminance and color are separate to begin with. If you are fortunate enough to have a DVD player with component video outputs (Y, R-Y, B-Y) and buy a TV with component video inputs, then use them. The biggest improvement in video quality will be seen going from composite video to S-Video, but there is still noticeable improvement by going from S-Video to component video.
Again, assuming that you will be using the TV for home theater, a built in surround sound system can be an important feature if you do not wish to add separate amplifiers and speakers. If you plan to go this route, you will need to ask about the specifications of the sound system (amplifier power to the various channels, and size of the speakers). More importantly, take the time for a serious listening demonstration with a good surround sound source (laserdisc). Turn up the volume in the store to make sure it does not sound boomy (like a drum) at higher levels. If it does, this is an indication of poor quality speakers and insufficient power. Voices, in particular, can be hard to understand at higher volume levels in an inadequately designed sound system. This is caused in part by "harmonic distortion" and speaker cabinet vibrations, factors I will discuss in later sections of the primer. Also listen for good separation of the surround sound to the rear channel (the rear channel has two speakers). Generally speaking, built in sound systems, whether they incorporate surround sound or not, are very limited in power and performance capability, so you should take this into consideration if you are going to be purchasing a separate surround sound system. There is no reason to pay for two surround sound systems if you are only going to need one.
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