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Dish Network Digtal vs. SDTV vs. HDTV

2295 Views 10 Replies 4 Participants Last post by  Mike123abc
How does the digital TV signal we get on Dish Network compare with the SDTV (I think this the correct term--I mean the over the air low end digital signal)?
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The digital resolution of Dishnetwork is not really the issue with the quality of the image. They seem to project a picture somewhere around 500x500 (someone probably will post the correct resolution). But, the issue is the compression that they do. It is a very subjective thing.

On an analog set about 30" in size, it is rare to see any compression. On an older 50" projection screen that is not digital, you see fairly mild compression effects.

On a 32" digital set, it is much easier to see the compression. I think this is due to the fact that the set faithfully produces each compression block (MPEG-2 divides the picture up into a grid and compresses the blocks individually). Most of the time you can see the blocks if you look for them. On a larger digital set it is very apparent. The more motion in the picture the more blocks you will see.

Now Dish is not alone in this, prior to dish I had digital cable. It was even more compressed than dish. I have basic analog cable (I switch back and forth to antenna (a very long story)). I can see some compression artifacts on the analog stations (cable digitizes them then converts them back at the neighborhood box). There are certain MPEG effects you can see besides the blocks (the analog cable stations are not compressed as much as dish).

If you get a good analog over the air picture it will blow away anything on dish except the HDTV channels. Over the air HDTV is another step up.
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Well it depends on your "digital" set. If your set does a really good job of reproducing the signal it is provided, you will notice the pixel blocks. The problem is that older analog sets do not have that high a resolution, the lines of resolution of the old are below what dish puts out, so you get a blending of the blocks by your set.

The set I have the most problem with is a sony XBR it does 1080i. The grain is so fine on it (pixels are really small so that more fit on the screen for higher resolution) that you can easily see all the digital effects. It helps a lot to turn off all edge processing. The softer you make the picture on the set the less you see the mpeg effects (because you are effectively reducing the resolution of the set).
Note that even though standard tv is 720x480, unless you have a good over the air reception, you probably never see it. Cable is compressed in most areas also. The cable companies digitize and compress the locals, send them over their fiber backbones then a local box in the neighborhood converts it back to analog for the non digital stations. This gives a far better picture than trying to amplify and spit the signal over and over from the cable company to the home.

DVD is highly compressed also, but most studios work for weeks to get a great picture, they hand sequence some frames even to try to eliminate as many artifacts as possible.

The compressors that Dish (and the cable companies) have to use have to do it in real time. No chance to superoptimize the compression. Compression hardware has significantly improved over the years, allowing them to put more channels on the same transponder.

HDTV is also compresses, but the bit rate is much higher so fewer artifacts.
The tuner/mpeg decoder that the FCC is mandating will be for decoding over the air digital signals. The set makers will still probably include analog tuners since the market pretty much demands that at this time.

Now the decoded digital signal can be anywhere from 720x480i to 1920x1080i (about 18 different combinations of refresh rates, resolution and interlaced/progressive). They will be scaled to what the TV can display. If it is a standard picture tube it will probably be scaled to somewhere around 720x480i. But, small screens and cheap tubes may only display an effective picture of 400x300 or less. It is a long discussion of what TV resolution is and displayed resolution. The TV standard dictates how many times the electron beam sweeps across the screen, but it does not mean that there is enough phospher on the screen in small enough pixels to display it all distinctly. Even sets listing 1080i may actually only display 1200x900 or less effective resolution.

Some display technologies have an exact pixel count that can be counted like LCD flat screens and plasma displays. Tube type technologies like rear projection and regular screens usually measure resolution by how many distinct lines can be shown on the screen.
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