Video This and That
Some more queries from readers about
various aspects of today's video scene:
I have a 40" direct-view TV and hope someday to buy
an HDTV direct-view set or some kind of widescreen flat display. But I don't want to give
up the height that I'm used to. What screen size do I need to look for in a widescreen
HDTV set so that it can have the same height as my present screen?
Screen sizes for widescreen televisions, with an aspect
ratio of 16:9, are measured in exactly the same way as for conventional 4:3 sets,
diagonally from one corner of the viewable area to the other. But because of the different
shape, a widescreen set will be considerably shallower and somewhat narrower than a 4:3
set with the same numerical rating.
I won't bore you with the arithmetic, but there are some
simple numbers you can use to compare sizes.
In my view, the greatest impression of size is the screen's
height: Letterboxed images on even large normal sets tend to look dinky. To find out what
the height of a widescreen set would translate into in ordinary terms, multiply by
approximately 80%. A 27" widescreen model would have a picture only as deep as a
22" standard set.
Put another way, to get a widescreen as deep as that of a
27" 4:3 set, you'd need one with a diagonal measurement of about 33" (multiply
by 1.22). In the case of your 40" requirement, you will need a widescreen measuring
49 or 50 inches.
The image size of a 27" widescreen is about the same
as a letterboxed image on a 30" normal screen, assuming the same 16:9 aspect ratio.
I am considering the purchase of a digital satellite
system. The product info indicates that I need an "unobstructed view to the
south." I live in an area with quite a few trees. I would mount the dish on the
rooftop but there would still be some foliage in the way. How critical is the unobstructed
view to the image quality?
A little foliage may not be a problem; buildings and
mountains are another matter. The dish only needs a small window to see through, so it's
usually possible to position it so the signal is unobstructed. Also, the farther south you
are, the higher the dish has to be aimed so it may well be that the angle plus the height
of your roof is enough to clear the treetops.
Obstructions, incidentally, are more likely to interrupt
the picture than degrade its quality. The same is true of things like heavy rain.
I have read that connecting a video source to a TV via
an RF cable would yield a maximum horizontal resolution of 330 lines, even if the source
is a DVD or satellite receiver, and that the sound would be mono even if both the set and
the source are capable of stereo. If that were the case, why would manufacturers make
machines with only RF inputs and outputs?
You're correct on both technical counts, in my experience.
The resolution is equivalent to a good off-air signal, and is about the maximum most TV
tuners can handle. As for stereo, it would involve considerably more complex circuitry in
a disc player, and I imagine that manufacturers assume that anybody interested in taking
advantage of the higher performance available wouldn't be using RF connections anyway. In
fact, except perhaps for the very lowest models, it's very unlikely that any manufacturer
of VCRs -- or any video component -- would provide only RF outputs today.
When a widescreen-format DVD is being played with a
black area above and below, are there still 480 (but thinner) lines in the viewing area,
or is the picture now being displayed with fewer horizontal lines?
When you watch a widescreen movie on a conventional NTSC
television set, only those scanning lines in the middle of the screen are visible; the
others are still there, but receiving no signal. Thus, a widescreen image has
significantly lower vertical resolution than the equivalent full-screen image. This can be
quite drastic. If the movie was shot in Panavision -- the most common widescreen technique
for theaters -- only about half the scanning lines are used. None of this is true, of
course, with high-definition digital signals.
...Ian G. Masters
ian@mastersonaudio.com
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