Techno-babble

Various Ramblings about HDTV

The end of analog broadcasting is near!
All analog television broadcasting in the USA is scheduled to end on February 17, 2009. Digital Television (DTV) will become the only television broadcast system used in the USA at this time. In our market, KTVL (10), KDRV (12), KOBI (5), and KMVU (26) will turn off their analog transmitters at the same time. We will continue to broadcast our normal programs, but only on our digital channels. If you have not purchased a digital tuner for your analog set before this happens, you will see nothing but snow when you turn your TV set on that morning.

Why should you care?
Anyone using a TV antenna to receive over-the-air broadcast television will see nothing but snow on their analog TV sets after this date. This could result in a lot of very unhappy people, especially if it comes as a complete surprise. About 20 to 30 percent of the population relies on over-the-air broadcast for their Television programming (not everyone is connected to cable or satellite!).

If you subscribe to cable or satellite, you may not notice anything happened on February 17, 2009. However, any analog TV set you own that is not connected to the cable or satellite system (a TV set in the kitchen for example) will display only snow. The cable and satellite companies have a lot to do before February 17, 2009 to make sure that their systems will continue to have the local stations available. They will have to switch to our digital signal since our analog signal will no longer be there. This is a lot easier said than done, especially since every analog TV station in the entire nation will be turned off at the same time.

The real deal:
You do not have to purchase a High Definition TV set in order to continue watching broadcast television after February 17, 2009. All you really need is a digital tuner connected to your analog TV set. Although a digital tuner connected to an analog set will never display High Definition (HD) pictures, you will be able to watch a Standard Definition (SD) version of our programming. You can still watch TV, which is all that really matters.

The bad news is that every analog TV set in your home will need its own digital tuner. If you have more than two analog TV sets, this could get expensive real quick. There are now SDTV sets available with built-in digital tuners starting at $250. Since a digital tuner costs about $200, you may be better off just replacing your old analog sets with a new SDTV set with built-in digital tuner.

More Information than you asked for:
The National Association of Broadcasters (NAB) has established a website that contains a lot of information concerning the end of analog TV broadcasting. This site also contains information on the "coupon program" that the government has set up to assist consumers in the purchase of digital tuners. Rather than repeat this information, we refer you to: http://www.dtvanswers.com/.

Alphabet Soup: DTV - HDTV - SDTV - EDTV
"Digital TV" (DTV) refers to how pictures are transmitted to your home and how you receive them. DTV is the new method of sending television signals to your home (the old method being "analog"). You must have a digital tuner in order to pick up digital signals. This holds true regardless of where the digital signal comes from, either over-the-air ("free TV"), cable, or from satellite. Although there are major differences between an over-the-air "digital tuner" and the "converter box" you get with cable or satellite, they are really just different versions of the same thing: a digital tuner.

HDTV (High Definition TV) refers to picture quality, not how the picture gets to your TV set. HDTV is supposed to mean a picture that is shaped like a movie screen (16x9 format) with much higher resolution (clarity) of an analog picture.

SDTV (Standard Definition TV) also refers to picture quality, and is supposed to mean a picture that has about the same clarity of your current analog TV set (4x3 format). SDTV can also be in the 16x9 format (such as "wide screen" DVD movies).

EDTV (Extended Definition TV) is a term describing a picture that uses the "progressive scan" (480p) display method (such as a DVD player). The picture from an "interlaced scan" (480i) DVD player would be called SDTV. An EDTV picture does look better than an SDTV picture, but it is not HDTV.

DTV Picture Formats:
Just because someone is transmitting DTV does not automatically mean that the picture you see on your digital set will be High Definition TV. There are 18 different picture formats that can be transmitted, but only 6 of them are High Definition. The remaining 12 picture formats are different forms of SDTV. Most of these SDTV formats result in a better picture than what you see on your current TV, but they are not HDTV. Some SDTV formats are for compatibility with the computer industry.

For a brief introduction to the various picture formats, visit http://www.avdeals.com/classroom/what_is_dtv.htm. For "the full story" about DTV technology, visit http://www.avdeals.com/classroom/what_is_dtv_full.htm. Both of these sites are a little old, but most of the information presented is valid.

The signal we transmit on our digital channel is made up of ones and zeros, just like your home computer and all other "digital" equipment use. Since DTV is digital data, a lot of stuff can be put in there; we could broadcast up to six SDTV stations on our digital channel. In our case, we have one HDTV station and two SDTV stations on our digital channel, thus showing three different programs at the same time. These different programs are called "stations" to differentiate them from our digital broadcast channel. These "stations" are called "10.1" (CBS in high definition), "10.2" (The CW), and "10.3" (CBS in standard definition).

Your HDTV set may use a dash (-) instead of a dot (.), but you get the idea. If your set uses an "on screen channel guide," you can select these channels from the menu. When we are not broadcasting true HDTV on our main DTV channel, we will be showing our current analog (channel 10) picture that we have converted to digital. Converting our analog picture to digital does not make it HDTV, but it does look better than our picture on the analog channel. There is no snow, impulse noise, or picture degradation as there is using the analog transmission system. But it is not HDTV. It is SDTV.

Currently, our only source of HDTV programming is the CBS television network. We have no local HDTV capabilities do not anticipate the purchase of any for a year or more. You can go to http://www.cbs.com/info/hdtv and see the CBS primetime lineup with all the HD shows highlighted.

1080i, 720p, 480i, 480p:
These are the most often used of the 18 possible digital picture formats. 1080i and 720p are High Definition picture formats, while 480i and 480p are SD formats. The number portion of these formats is the number of active video lines used to make the picture. The letters represent the method used to "paint" the picture on the screen.

Any picture you see on a television set is made up of horizontal "lines" of video, which are painted on the screen from the top to the bottom. In the interlaced format, the odd numbered lines (1, 3, 5, ...1079) are painted on the screen, then the even numbered lines (2, 4, 6, ... 1080) are painted in between the odd numbered lines. In the progressive format, all lines are painted in numerical order (1, 2, 3, 4, 5, ...720). A better explanation of how television works is available at http://electronics.howstuffworks.com/tv.htm. An article on how HDTV works is available from the same people at http://electronics.howstuffworks.com/hdtv1.htm. Both articles are rather long, but worth the effort.

The progressive scan format usually makes a more pleasing picture when rapid movement is involved. The problem with the progressive scan format is that it takes more "bandwidth" or a faster "data rate" than does the interlaced format for the same number of active video lines. We broadcast in 1080i mostly because the CBS network uses the 1080i format.

You would think that 1080i would look a lot better than 720p since there are 360 more video lines in the 1080i picture. But the advantages of the progressive scan format almost makes up for the missing video lines when there is movement in the picture. You really have to look close to see that the1080i picture actually does look better than the 720p picture. But it is there if you look hard enough.

All of our High Definition programs are broadcast using the 1080i format. When we are not broadcasting High Definition, the picture you see is in the 480i format.

If you have watched our digital channel you may have noticed that your digital set says that we are always broadcasting a 1080i signal, even when you can see that we are obviously broadcasting an SDTV picture. We have set our digital encoder (the device that makes our digital picture) to "insert" our 480i picture in the middle of a 1080i signal.

We do this to keep your TV set (and our encoder) from having to switch formats every time we change from a High Definition picture to an SDTV picture, and back again to a High Definition picture (every commercial break). It can take 2 seconds or more for your set to recognize the command and then change the display format. It also takes a few seconds for our encoder to change the format. This really looks bad as the picture on your set usually freezes and "pixilates" during the change. Therefore, we don't change encoder formats very often.

No doubt you have noticed that our SDTV pictures always have "side bars". Some stations stretch their 4x3 analog pictures to fill the 16x9 screen. This "stretching" of the video results in a distorted picture, and it also reduces the resolution (clarity) of the picture. The edges of the picture are stretched more than the center to limit this distortion, but we still didn't like the resulting picture. Also, the top and bottom of the picture usually gets "chopped off".

There is one other reason we don't try to fill up the screen when broadcasting an SDTV picture. If those sidebars are missing, you know that the picture is true HDTV, not some SDTV picture stretched to fill the screen and pretending to be HDTV.

There is one exception to this rule. Sometimes we have a program (usually a movie) that is only available in analog "letter box" presentation. We will stretch the picture to fill the 16:9 screen for these programs. If we did not do this, the "letter box" picture would show up on a 16:9 set with black bars on the top and bottom of the picture, as well as both sides. In other words, you would get a "postage stamp" picture on your HDTV set. This is not acceptable to most viewers, or to us.

We change the aspect ratio of our encoder to fill the HDTV screen for this reason, although it is not in HD. The letterbox mode does not distort the picture much, but it does decrease the resolution a tad.

HDTV is HDTV is HDTV is HDTV...
A High Definition picture should look the same regardless of where it comes from (over-the-air, cable, satellite, or an HD-DVD). The only difference between an over-the-air, cable, or satellite HDTV picture would be which compression scheme is being used. All HDTV pictures are compressed, which is a method used to reduce the amount of digital data that must be sent in order to make an acceptable picture.

Satellite and cable systems usually use a higher compression scheme than does broadcast. Sometimes this causes a noticeable reduction in the picture quality, and sometimes it causes the picture to freeze intermittently. Most of the time, the picture is fine. Broadcast digital pictures can also experience the same problems when there is a lot of fast motion in the picture, but it normally does not occur as often.

Native format:
All digital sets have a "native display format" (also called "native resolution"). It is much easier (and LOTS cheaper) to change video formats in digital memory than it is to design the set to actually be capable of displaying the 18 possible video formats.

Your current analog set also has a "native display format". Over 50 years ago, the National Television System Committee (NTSC) set the US analog broadcast video standard as 525 interlaced video lines, 30 frames per second. All analog television sets sold in the United States are built to display pictures using this standard. Other parts of the world use different video standards such as PAL and SECAM (among others). All US analog television stations as well as cable and satellite systems must send their pictures to your analog set using this NTSC "standard format". In the case of "digital cable" and "digital satellite" the STP (Set Top Box) changes the digital signal to an analog picture for display on your analog TV set.

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