OTHER TECH

Great Expectations

Q. I'm shopping for a 37-inch widescreen LCD HDTV. In one store, a sign warns that the images LCD TVs display are high-definition and that if you're receiving standard cable or broadcast TV you may be "disappointed" with the picture. The implication is that the picture may not be as satisfying as what I'm now viewing on my CRT set, which I do consider very good. Can that be true? And in what respect might it be inferior? I watch my current 27-inch set from about 10 feet away, and I intend to remain at that distance. L. Wallcave Santa Rosa, CA

A. Al Griffin says: A common misconception about HDTVs is that they make all pictures, including standard-definition ones, look like they were shot in sparkling high-definition. That's the likely reason some stores post "warnings" next to HDTVs - they don't want to deal with returns from unsatisfied customers expecting magic tricks from their costly new set. The video processing circuits in HDTVs can't actually add any detail to standard-definition pictures; they just interpolate between the available pixels in the original signal. If the processing is performed well - along with the added benefits of noise reduction and detail enhancement - the picture can look pretty good. But if it isn't, the picture probably won't look any better than what you'd see on your old tube set, and it may look worse.

Either way, the differences between standard and high-def programs won't be that apparent when viewing from a 10-foot distance, which is farther than recommended for watching HDTV on a 37-inch screen. (A more appropriate maximum viewing distance for that screen size would be 7.5 feet.)

Hum Dinger

Q. I have a ground-loop problem that results in a hum from my subwoofer when I connect my cable feed to the TV. I bought a ground-loop isolator for the coaxial cable line and it did cut out the hum, but it also cut out a couple of my high-def channels. Is there a better solution? Rick Hermann Green Bay, WI

A. Ian G. Masters says: There must be. A solution to one problem that actually cripples the functioning of another part of your system is no solution at all. The problem may be that the isolator you bought does not have enough bandwidth to pass the high digital-cable channels. In that case, a wide-bandwidth device such as the Jensen Transformers model VRD-1FF probably would do the trick. But there are other possible approaches.

Ground loops are caused by components in a system being connected to "ground" at points that actually have small differences in electrical potential, which results in an AC signal passing between them, amplified as hum. It could occur anywhere in your setup but show up only in the subwoofer, which may be the only speaker able to reproduce a signal at line frequency. Since there have to be two ground connections to create the situation, the key is breaking the ground somewhere to get rid of the hum. This is notoriously difficult to do, but I'd start by simply disconnecting everything and hooking it all up again anew. If that doesn't work, you're in for a tedious process of trying to isolate the location of the problem, component by component.

Sometimes the old trick of installing a 3-prong to 2-prong AC adapter to "cheat" the ground on the power cord of a suspect component can break the loop, but beware: That ground connection is there for your own safety and that of your gear, so defeating it is not an ideal option.