What causes mosquito/digital noise? (MPEG4 vs MPEG2) - AVS Forum
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post #1 of 5 Old 05-21-2011, 10:41 AM - Thread Starter
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I'm still comparing Dish Network and Comcast and I've noticed a few things:

1) Dish Network has a softer image. (perhaps because they use a lower resolution for HD content [1440 vs 1920])

2) Comcast's SD is literally unwatchable (for me). During motion there are lines that appear (hard to describe) and it's actually quite nauseating.

3) Comcast has more "noise" in the picture. I'm not sure if that's because it has a more accurate picture (than Dish Network) and the source material has noise (ie. analog-to-digital HD programs) but Dish Network kind-of hides most of this noise (because it's softer?)

Anyways - what is the cause of this noise? Is it because of too much compression? Is the noise actually a good thing? (ie. more accurate from the source material?)
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post #2 of 5 Old 05-21-2011, 05:26 PM
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Quote:
Originally Posted by sofakng View Post
Anyways - what is the cause of this noise?
The noise is an artifact of the compression process. MPEG2 uses Discrete Cosign Transforms (DCT) to compress the video. Mathematically, the characteristic of DCT is to create a series of coefficients that get closer and closer to zero as the number of coefficients increases. The compression occurs when you drop some of the smallest coefficients. If you drop too many of the coefficients, you get a very low bandwidth, but with the mosquito noise that you notice.

http://en.wikipedia.org/wiki/Discrete_cosine_transform
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post #3 of 5 Old 05-21-2011, 05:52 PM - Thread Starter
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Wow - thanks for such an informative reply!

That helps my decision quite a bit. I was thinking that Comcast had a more accurate picture but now that I know the noise is from MPEG-2 compression that changes things quite a bit.

I'll probably take the Dish Network picture even though it's softer because it doesn't have nearly as much noise, etc.
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post #4 of 5 Old 05-21-2011, 11:00 PM
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Have you read this thread?
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post #5 of 5 Old 05-22-2011, 01:39 PM
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Quote:
Originally Posted by sofakng View Post

Wow - thanks for such an informative reply!

That helps my decision quite a bit. I was thinking that Comcast had a more accurate picture but now that I know the noise is from MPEG-2 compression that changes things quite a bit.

I'll probably take the Dish Network picture even though it's softer because it doesn't have nearly as much noise, etc.

From those on the forum who have compared both Comcast HD is generally considered better.

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