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Updated on July 18, 2009

What’s the difference between SDTV, EDTV, and HDTV

There remains confusion as to what these terms mean. To understand the differences, think of it as part of the story of television. Once upon a time there were standard televisions (SDTV). No one called them standard televisions at the time, or SDTV, because they were the only types of televisions out there. Broadcast signals were sent in an interlacing feed or signal. To place one frame (think of the old movie rolls) on your set, your SDTV has to fill in 480 horizontal lines of information. Just like a painter, the signal sweeps over the screen twice. The first time it inserts the information into the odd numbered lines from 1-480, and the second time it fills in the information into the even numbers from 1-480. It takes 1/30th of a second to do these two passes. Then, the SDTV interlaces the two and voila, there is one frame on your television (like when you press pause on your DVD, TV, or VCR today). So basically interlacing runs across your screen twice in order to make one frame. SDTV’s have 480 interlacing lines; hence 480i., where the “i” stands for interlacing.

Since the 1950’s, this 480i format has been wonderful. Now here is where the story takes a new turn. Televisions became bigger. The majority of them had been 18-25 inch, but when the big ones came out, 40-50-60 inch, a problem developed. The images looked horrible on SDTV’s. You could see the jagged edges where the two interlaced signals met together, larger blown-up images had extra “artifacts” in them, and the scan lines themselves could be seen. On the other side of the equation, the DVD revolution was providing theatre-like signals that were being wasted on these low-capacity SDTV’s.

The solution to this conflict was to get rid of interlacing signals and change them to progressive signals. Progressive feeds consistently progress down the screen from top to bottom, filling in all the information. There are no more jaggies or screen errors. They named this signal 480p, because it still filled in the 480 lines, but did it much better. The “p” stands for progressive. They called these tvs EDTV, or Enhanced Digital Televisions. Another benefit of this development was the fact that bigger screens over 50 inches looked incredible.

So, then what is HDTV? In the last five years, High Definition televisions have come out. They basically double the amount of lines on the screen, going from 480 up to 1080.They can use a variety of signals, but can receive signals at 1080i, or 1080p. There is very little difference between the quality of image between these two signals unless you have an enormous television of over 60 inches. The other benefit of an HDTV is that they can widen the screen from the standard box shape (4:3) to a more theatre-like size (16:9). The picture quality of shows, movies, and DVD’s look amazing, like you are sitting in a movie theatre. But even if you have an HDTV, if your other equipment is not updated, or if your programming package is not correct for HDTV, the picture will look worse then it had been before with SDTV.

Beware of the Signal

You plop down in your favorite chair, give an authoritative voice command, and your new HDTV turns on. You grab your sandwich, flick open your soda, and push back into your recliner. Wow. The commercials look fantastic. Look at how much detail you can see. The clock on the wall shows that it’s the top of the hour. Here it is….what? There are sidebars on the screen. Is this mini-HD? It says at the bottom of the screen, …now in full HD.

Welcome to the HDTV Transition age. Just because you purchased an HDTV and were smart enough to update your cable or satellite package does not mean that you will view everything in HD. Many commercials are in HD, on HD channels, and the overall broadcast signal from the station is in HD, but the program may not be.

Each broadcast company either collects or broadcasts its own programs. If a program is popular, and not available in HD format, they still will probably show it. You are ahead of the curve and need to be patient, unfortunately. In time, a specific broadcast station like ESPN, or TMC, or your local CBS will buy enough equipment to shoot, develop, and broadcast every program in High Definition. But until then, you may see your screen jump around in different configurations as it tries to process the different feeds or signals that it is receiving from your cable or satellite box.

All broadcasts as of June 2009 are in digital (not analog anymore) but that is different than high definition. Digital feeds provide for the opportunity to broadcast in HD, but that doesn’t mean that a particular broadcast channel could afford to, or that every show will be in HD.

If you get to know the different broadcast companies and channels, you will soon learn which ones can be trusted to broadcast the majority of their shows, or your favorite program, in HD.

The smartest move you can make during this time is if you are considering purchasing a new HDTV, research which models have the best processing chips for analyzing signals. Also, some HDTV’s show standard broadcast signals better than others. Mine does, does yours?


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