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Home Theater Hacks by Brett McLaughlin

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Hack #35. Resolve Problems After Buying an HDTV

There are a handful of tips you can follow and tweaks you can make to your setup after adding HD-capable devices. These are fairly random but all together they can make a huge difference in quality and operability.

No matter how much research you do before buying a TV, you're still almost guaranteed to have a few surprises and problems when you break the set out of its box. This hodgepodge of tips and technical explanations will help you solve the most frequent issues you'll run into.

Bridging Component Video and VGA Connectors

You've just brought home a new unit, and you've discovered that your HDTV requires a VGA cable, while your receiver offers only component video connections (or the other way around). Some manufacturers have anticipated this situation, and have designed their sets to break the rules, in a manner of speaking. That is, some VGA ports might allow syncs on the green wire.

Tip

For VGA, Hsync and Vsync are the fourth and fifth wires (remember that VGA connectors have five cables). In component video, these syncs are multiplexed onto the green wire (labeled Y in a Y-Pr-Pb system).

For example, my TV set will accept component video force-fed into its VGA port. There was nothing in the set's instructions about this, but I found a menu item that allowed the set to accept green-wire syncs.

If the unit literature says nothing about this, ask the "expert" at the store where you bought the TV. If the sales staff doesn't know anything about such an option, you can experiment. Adapters that might work are available via the Internet. An alternative to the adapter is to get a VGA cable that has five BNC connectors on one end, and then get three BNC-to-RCA adapters from RadioShack. These cables probably will cost around 50 bucks, but you can often return the cables if things don't work out.

Understanding Subchannels

Let's say the FCC has given the NTSC station on channel 3 permission to use channel 41 as a digital (HD) channel. So, you tune to channel 41, and your new receiver says you are now on channel 3-1. To add to the confusion, you also have discovered there is a channel 3-2. What are these channels and how did they get there?

You've discovered virtual channels. A virtual channel is a physical channel with a different name or number. The physical channel refers to the actual RF spectrum being used. The virtual channel could be called almost anything. In this example, 3-1 and 3-2 are virtual channels, and also are referred to as subchannels of virtual channel 3, which is physical channel 41. And just to confuse matters a little more, these virtual channel 3s have absolutely nothing to do with an analog station that is on the physical channel 3.

The data stream of DTV channel 41 has data blocks called PSIP data. The PSIP data tells the receiver that channel 41 has two subchannels: 3-1 and 3-2. The channel 3 people choose these subchannel names to remind you whom you are watching. However, not every station follows the example of this hypothetical channel 3; a different management might choose 41-1 and 41-2 for physical channel 41's subchannels.

Your remote control will let you key in either the physical or the virtual channel number, but there are some differences between manufacturers. For example, some cable/satellite receivers will assume 3-0 means analog channel 3, while others will try to locate a virtual channel 3 for the same key sequence.

Why Can't I Get My Local DTV Station?

Your first days with your new HDTV can be a very confusing and frustrating time, particularly where OTA stations are concerned. You can't tell your receiver that a channel is digital; the receiver has to figure out for itself whether a physical channel is analog or digital. If the antenna is getting a marginal signal or is mis-aimed, the receiver often guesses incorrectly. You then can't aim the antenna because the receiver thinks the channel is analog, and you can't convince the receiver to switch because the antenna is mis-aimed. In strong signal areas, the receiver might eventually right itself. Otherwise, you might have to figure out how to make the receiver unlearn a channel (consult your menus and documentation). Even if you get this fixed, though, you're still going to have a mis-aimed antenna.

Nearly all DTV receivers have a signal strength meter of some type. Most of these meters read zero until the signal is good enough (or almost good enough) for reception. In weak signal areas, these meters won't tell you much about whether you need your antenna to aim more to the right or to the left. When you get no reception, you are left not knowing whether your antenna is just mis-aimed, or if the signal strength is inadequate. As you might guess, this leaves a lot of room for guesswork and can lead to plenty of frustration.

The good news is that once the receiver has learned all the channels correctly, these problems are gone forever. In fact, people in areas with strong signals will never see most of these problems to begin with. All receivers have a channel learn sequence, in which the receiver will search for and learn all available OTA channels at once.

Tip

When you initiate this learning sequence, some receivers will forget everything they learned previously, which creates problems for users who use a rotor or who switch between two antennas. These users will need to learn how to add channels manually.

Picture Quality

The image quality of an HD picture isn't affected by a low to moderate level of noise in the signal. This is true for both satellite and OTA DTV. Yet some people can't resist wondering whether some antenna tweaking would improve the signal strength and result in a better picture. The answer, without any hedging, is that this sort of tweaking will have no effect on picture quality.

When the signal for a channel becomes too weak to display, you will see macro-block errors—parts of the screen will be shifted or out of place—and you will experience sound dropouts lasting a few seconds, as well as image freezes lasting a few seconds. All of these errors are crude, unsubtle errors. If these are not present, your image is perfect. You either get the picture, or you don't.

Once you're at this stage, there is still one reason you might want to try to improve the signal: you might be able to decrease the chance of dropouts in bad conditions, such as heavy rain. Rain can affect DBS and UHF reception, but not VHF. In some places, wind can affect UHF.

Warning

If you get sound dropouts but not image dropouts, or vice versa, the fault is not a reception problem. Usually the station is at fault, but occasionally it is the set top box [Hack #30] .

Determining Display Resolution

It's often hard to tell if you've got a picture in full-blown 1080i, or if you're seeing 720p [Hack #1] , or just plain old 480 (progressive or interlaced). When a TV station decides to provide an HD subchannel, that subchannel is normally 1080i (or 720p) all the time at the transmitter, even if some of the programming originates from NTSC cameras that can't capture HD images. There is no technical requirement for this, but it seems to be nearly universal practice. Thus, your receiver's HD detector is not a reliable indicator of whether the program is actually HD. It will pick up the transmitter's information rather than the format of the source material.

Tip

NTSC 4:3 images often have black bars on the side that you might not be able to eliminate because they are part of the 16:9 transmitted image.

So, what is the most reliable way to tell if you are seeing true HD? If the image is 16:9, the image is not stretched, and there are no black bars on the sides, you're almost certainly looking at an HD image. ABC and ESPN typically are sending in 720p, and most other carriers are sending 1080i images.

Waiting on Local Networks to Broadcast in HD

All DTV transmitting equipment can handle HD at no extra cost. The only extra cost associated with passing on HD information is that associated with staffing two sets of transmission procedures. However, the cost of the DTV transition has hit the local stations hard, and some are resisting even this small expense.

Also, many of the newest DTV stations are rural stations. Rural stations often don't have HD taping equipment, let alone a staff that can operate this higher-end gear. So, if you're not in a larger city or television market, you might be stuck pulling in HD from a satellite provider for a while.

Grabbing HD Local Channels Through Satellite Providers

As you've no doubt figured out, most satellite providers give you local channels through their feeds, usually for a nominal cost. It would stand to reason, then, that HD versions of these local channels would soon follow. That turns out not to be the case, though, and probably won't be for several years. An HD channel requires about five times the bandwidth of an SD channel. To convert all their local channels to HD, DirecTV and DISH Network would each have to launch several more satellites.

Tip

Both companies are very secretive about their future plans

Another seemingly good idea would be for satellites to simply pass through local channel HD feeds, supplying consumers with a single source for all programming (the satellite dish, as opposed to requiring both a dish and an OTA antenna [Hack #33] ). However, the National Association of Broadcasters lobbies effectively for local stations. As a result, Congress has legislated that these stations continue to enjoy their monopolies, and disallows satellite providers from passing on their feeds. In most cases the satellite operators are forbidden to offer viewers feeds or stations that would compete with the local channels.

The only exception in this area, at least right now, is CBS. CBS-HD is available on DirecTV and DISH Network. But to qualify for this, you probably will need a waiver from your local CBS station.

Getting Rid of Artifacts

In image processing, an artifact refers to any predictable flaw in the image that results from shortcuts or shortcomings in the processing technology. In HDTV, most artifacts result from compromises that have to be made when the picture changes too rapidly and requires more than the allowed band-width. Sometimes the solution to these bandwidth limitations is to delete frames, while other times the choice is to randomly delete 16x16 macro-blocks. There are also a number of common artifacts that result from converting 24 frames/sec films to 30 frames/sec TV broadcasts; this category of artifacts generally is not something related to bandwidth, and probably will be solved as conversion processes improve.

Tip

Snow and interference generally aren't called artifacts.

It's also not uncommon for a particular HDTV set to introduce some artifacts of its own. If you see these consistently, on multiple channels, contact your set manufacturer and see if you can get some resolution. You might also be trying to view broadcasts at a higher resolution than your set supports (although this is rarely the case with any but the first-generation HDTV sets).

The Problem with SD Programming

In cases where SD programming is pushed out via an HD broadcast, you can get an almost unheard of phenomenon, at least in HD programming: snow. Remember I mentioned earlier that either you get an HD picture, or you don't. That's true, but SD programming over an HD transmission is a bit of an exception. This is a consequence of the change in the bandwidth between recording and playback. Although the bandwidth of SD is said to be 5 MHz, it is not a sharp cutoff. The roll-off starts before 5 MHz, but some image information above 5 MHz survives the recording process, albeit mixed with electrical noise (which shows up as snow). The broadcaster has to decide if she wants to filter out this snow or leave it in. If the broadcaster decides to filter out the snow, some image information is lost, resulting in increased blurriness. Because this is a trade-off, different broadcasters will make different choices.

There has been a significant improvement in the average quality of NTSC broadcasts over the last three years. There are two reasons:

  • True SD resolution (640 x 480) used to be a target TV production crews believed they had to aim for but didn't really have to meet. Their product often was well below 640 x 480, for a variety of reasons. But now, with large, high-definition sets becoming common, these production people are seeing how bad their product can look, and are paying more attention to the details (camera focus, circuit noise, cable reflections, filter circuit selection, etc.).

  • Many people are watching NTSC broadcasts of shows that were shot with high-definition equipment. These situations always reveal any deficiencies in the SD source material.

—Kenneth L. Nist

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