MINNEAPOLIS (AP) — In Brent Swanson's basement home theatre, there should be nothing drab about "Battlestar Galactica." He's got a high-end projector that beams the picture onto a wall painted like a silver screen, and speakers loom in the corners, flanking two big subwoofers.

Yet when he tuned in Sci Fi HD for a recent episode filmed in high definition, the image was soft and the darkest parts broke up into large blocks with no definition. Explosions, he said, were just dull.

"It kind of looked like they took the standard definition and just blew it up," said Swanson, a 33-year-old graphic designer and videographer who subscribes to Comcast Corp.'s TV service. "I couldn't really tell if what I was seeing was really better than what I saw on regular television."

As cable TV companies pack ever more HD channels into limited bandwidth, some owners of pricey plasma, projector and LCD TVs are complaining that they're not getting the high-def quality they paid for. They blame the increased signal compression being used to squeeze three digital HD signals into the bandwidth of one analog station.

The problem is viewers want more HD channels at a time when many cable and satellite providers are at the limits of their capacity, said Jim Willcox, a technology editor for Consumer Reports magazine.

"They have to figure out a way to deliver more HD content through their distribution networks," he said.

Compressing the signal is cheaper than costly infrastructure upgrades to increase capacity. Satellite TV providers — including DirecTV Group Inc. and Dish Network Corp. — also have the option of launching satellites to boost the number of HD channels on their systems.

While information is nearly always lost when signals are compressed and then uncompressed, the process can theoretically be made unnoticeable to eyes and ears — and Comcast says it should be.

But some viewers say they can see it. Willcox said complaints about compression have been showing up on web forums, including the AV Science Forum, a site for serious audio visual enthusiasts.

"It's not exclusively Comcast, although Comcast, being the largest cable provider, is probably the largest target," he said.

Derek Harrar, a Comcast senior vice-president in charge of video, said the company recently began using new technology on some channels to compress three HD channels into the bandwidth of one analog station. Other channels continue to get the previous two-to-one compression.

In a posting on the AV Science Forum, Ken Fowler of Arlington, Virginia, compared Comcast signals with those on Verizon Communications Inc.'s all-fibre-optic network, which doesn't have the same capacity limitations. Fowler found the higher-compressed HD stations, including Sci Fi, Animal Planet, the Discovery Channel, the Food Network and A&E, fared particularly poorly.

He analysed the signals by recording them on a digital recorder, then transferring them to a personal computer for analysis. He found there was much less data, measured in bit rates, flowing to some channels than others.

For example, Discovery's bit rate was 14.16 megabits per second on Verizon's FiOS system but only 10.43 Mbps on Comcast; A&E HD was 18.66 Mbps on FiOS compared with 14.48 Mbps on Comcast. The FiOS system didn't offer Sci Fi HD, which Fowler's testing showed at 12.59 Mbps on Comcast.

He found the signals from the major networks and ESPN weren't getting the increased compression.

In an interview, Fowler said he reran his analysis about two weeks ago and found "basically the same thing".

Philadelphia-based Comcast wouldn't identify specific signals that are three-to-one compressed, and a Sci Fi channel spokeswoman referred questions back to Comcast.

Harrar said the company works to make sure any new compression technology is invisible to consumers, but Comcast is "constantly monitoring our network and making adjustments" for best picture quality. The company has been rolling out the new compression technology at different times around the country.