Ask S&V

Kurt Miller

As you probably know already, 7.1 places three speakers in front (left, center, right), two speakers to the sides (surround left and right), and two speakers in the rear (back surround left and right). To take advantage of this setup, you need content with 7.1 discrete channels of audio, which is practically non-existent—some Blu-ray movies have 7.1 channels, but virtually all of them have been artificially derived from the original 5.1 soundtrack. Alternatively, the AVR can synthesize the back-surround channels from a 5.1 source.

Either way, I'm not a big fan of 7.1 because it places more emphasis on the surround channels with four speakers than on the front three channels, which is exactly opposite of the way it should be. Humans have the ability to sense the direction from which a sound is coming, but this ability is much more acute in front of us than behind us. Thus, we don't need so many surround channels to convey a sense of envelopment. If we're going to add channels, they should be in front, not in the rear.

That's the idea behind Dolby Pro Logic IIz and Audyssey DSX. Dolby Pro Logic IIz is an extension of IIx, which can artificially expand two channels to 5.1; it can also expand 5.1 to 6.1 or 7.1. IIz adds the ability to synthesize two so-called "height" channels with speakers placed above the front left and right speakers, which is intended to enhance the ambience of the entire soundfield.

Audyssey DSX does much the same thing, but in addition to two height channels, it can also create what are called "wide" channels, for which speakers are placed outside the boundaries of the front left and right speakers. So if the main left and right speakers are at ±30 degrees from the center, the left and right wide speakers would be at ±60 degrees. Unlike Dolby Pro Logic IIz, Audyssey DSX requires a 5.1-channel input; it can't expand two channels.

As for which is better, that depends on your situation and preferences. DSX is more flexible, offering height and/or wide channels, whereas IIz offers only height. But Dolby can expand 2-channel sources, while Audyssey requires 5.1. In my view, either one is preferable to straight-ahead 7.1 because they add channels to the front rather than the rear.

Overcoming Overscan
Why do flat panels not have a function to disable overscanning? I would prefer to see all the resolution in the image rather than overscanning the image, which makes all the pixels homeless.

Rob Meulendijks

Actually, most flat panels do provide the ability to disable overscanning, a function that upscales the image slightly and crops off the edges in order to eliminate the "digital hash" that you can sometimes see on the edges of certain broadcast channels. However, this process also obscures the fine detail by remapping the pixels in the signal to the pixels on the screen. (I like your metaphor of pixel homelessness.) Ideally, you want each pixel in the signal to be displayed by the corresponding pixel on the screen—the pixel's true home—which can be achieved only by disabling overscanning.

Unfortunately, this control goes by different names, as does the correct setting, making this a most confusing issue. In a few displays, there's actually an Overscan control, which should be set to 0 or Off. More often, the control is called something like Size, Picture Size, or Aspect Ratio. The correct setting is often called something like Just Scan, Screen Fit, or Dot by Dot. In some cases, setting the control to 16:9 eliminates overscanning, but in other cases, this setting enables it.

The only way to be sure you've disabled overscanning is to display a pixel-cropping test pattern from a disc such as HD Benchmark, which reveals if any pixels are being cropped from the edges. While displaying this pattern, cycle through the settings until you find the one that causes no pixels to be cropped.

3D Without Glasses
I'm wondering about 3D TVs that don't require glasses. I was in Riyadh, Saudi Arabia, a few weeks ago, and they had a few of these on display in the mall. The display just said "Experience 3D" and didn't have any brand or manufacturer label on it. I thought they looked pretty good. From across the mall, it looked just like a normal 2D TV, but when you stood in front of it, the picture (which was mostly simple animations and such) suddenly popped into 3D. You had to stand in certain spots to see the effect, but several people could easily watch it at once. Standing the correct distance from the screen also seemed to help.

So my question is, should I wait for these to hit the market instead of the currently available ones that require glasses? After reading the reports from CES, I was under the impression they are still many years away, but seeing them in public scattered around the mall makes me wonder if they will be available sooner than I thought.

Jonathan Still

What you saw is called an autostereoscopic display, a technology that has been around for some time. A lenticular screen is placed in front of the image, which is similar in principle to the cards and toys with a flat, ribbed plastic surface that show one image when viewed from one angle and a different image when viewed from another angle. The ribs on the TVs you saw are much thinner than they are on those cards and toys, but the idea is basically the same.

Autostereoscopic displays haven't caught on for a couple of reasons. For one thing, you are correct that you must be in a particular spot to see the 3D effect, which is visible within a 10-degree "window" that repeats itself as you move off axis—this is why several people can see it at the same time. If both eyes are within one of these windows, it looks fine, but if one eye is in one window and the other eye is in the adjacent window, it looks really weird.

Also, this type of display cuts the horizontal resolution seen by each eye in half, which is not desirable. As a result, I don't expect these displays to become very popular in the consumer marketplace.

If you have a home-theater question, please send it to scott.wilkinson@sorc.com.