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EXPERTS DISCUSS COMPRESSION

JOHN SCIACCA Contributing Technical Editor Lead System Designer, Custom Theater and Audio, Murrells Inlet, South Carolina

From my own experience, I would argue that high-definition signals from cable-TV providers tend to be more compressed than those from satellite. At my home in South Carolina, I have a 61-inch Samsung DLP set and Time Warner cable decoded by a Scientific Atlanta HD cable box. At the custom-installation showroom where I work, there's an identical Samsung set fed by a latest-generation DirecTV satellite receiver. I routinely watch identical programming on Discovery HD and HDNet, and I notice far more compression artifacts at home on cable - most noticeably macro blocking whenever there's fast motion. The picture also suffers similar artifacts if a number of objects are moving at the same time. Of course, whether you see the same things will depend on your equipment and your program provider.

SEAN GREER Owner and Senior System Designer Experience AV Home Theater, Montrose, Colorado

Don't forget to clean up your signal path before trying to evaluate signal-compression issues such as block artifacts (which occur when moving areas of an image like fire break up into red and yellow squares). What's the native resolution of the material? Are you trying to display a 1080i signal on a TV that has only 720 or 768 lines of resolution? If so, your TV's signal processor might be compounding - or even creating - the problem. Even if your satellite receiver has been set for 720p to match your set's native resolution, it's still processing the native 1080i signal into another (720p) resolution, which could be introducing distortion into your picture.

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