From the NY Times:
Comcast’s Blurry High Definition Picture
By Saul Hansell
Not only has Comcast been slowing down Internet users exchanging files with the BitTorrent protocol, it has been quietly reducing the quality of some high definition television networks it carries as well.
Most people will hardly notice the change, and the HD channels affected are still a lot better looking that standard definition signals. But Ken Fowler, a devoted high definition video aficionado did. He had Verizon’s FIOS video offering. But he also signed up for Comcast’s service in order to watch the Washington Nationals in high definition. On some networks carried by both operators, Mr. Fowler noticed that the picture quality on Comcast was inferior.
“I noticed that there was more blurring in the movement and less detail on the screen,” he said. Mr. Fowler, a financial analyst by profession, started to measure the difference between the Comcast and FIOS systems. He posted the results on AV Science Forum, a Web site for hardcore video buffs.
In images he posted, MTV and Discovery, among others, are distinctly more blurry or blotchy than those on FIOS. This occurred mainly in scenes with rapidly moving images. This makes sense as video compression systems eliminate redundant information from one image to the next, which is fine for talking heads and such, but too much compression distorts pictures of sports and other action scenes.
Mr. Fowler recorded some of these programs and found that for some channels, Comcast was transmitting 20 to 35 percent less information. Some networks, including ESPN and the major broadcast networks were not degraded, he found.
Jenni Moyer, a Comcast spokeswoman, confirmed that the company, like all cable and satellite systems, does compress its signals, but it tries hard to maintain the quality.
“Compression is a reality: We use it and other providers use it,” she said. “Our goal is not to have any kind of noticeable impact on picture quality.”
At issue here is how cable systems manage the increasing number of networks broadcasting in high definition, given the limited capacity of their networks. Cable systems are roughly divided into 6Mhz channels, each representing the amount of space one traditional analog signal would occupy. Digital cable can squeeze ten to twelve signals of standard-definition TV in one of these channels. Until recently, most cable systems put two high-definition stations in each channel.
Now Comcast is putting three signals into some of its channels. And that causes it to compress the signals more.
Comcast is not alone. Time Warner is also starting to put three high-definition networks on some of its channels.
This made me wonder whether we are going to lose some of those wonderful networks that the compression of digital cable have given us, Animal Planet, Tennis, D.I.Y., Soap and so on—because the move to HD will use all the bandwidth these networks are using.
Not so, cable experts say. The easy way to free up space on a cable system is to eliminate the remaining few dozen analog channels. This will require more people to get digital set top boxes, but some systems, including FIOS are doing this to make more space for HD channels. Also, there is technology called switched video that changes which networks are on what channels depending on what people in a given neighborhood are actually watching. Proponents say that this approach can handle an infinite number of networks, even in high definition.
http://bits.blogs.nytimes.com/2008/0...ref=technology
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