ARTICLES
Connections (Sound & Vision Buyer’s Guide
2003)
Not so long ago, hooking up a TV set was petty simple. You had
antenna inputs, and if you had a high-end model, there might also
be a composite-video input and some audio outputs. But as video
sources and home theatre have proliferated, so have the varieties
of connections.
Today you can expect to find video connections in four flavors:
composite, S-video, component, and digital. Composite video is
the lowest common denominator. Originally developed for
broadcast use, it multiplexes the color and luminance portions of
an analog video feed into a single signal, which must be pulled
apart again in the TV tuner for display. Composite connections are
normally made via ordinary RCA jacks.
Because there are losses and artifacts associated with combining
and un-combining a composite-video signal, it’s better to keep the
luminance and chrominance elements separate, which is where S-
video, or Y/C, connections come in. The “S” stands for
“separated,” and small, round multi-pin jacks and plugs are used
to carry S-video signals. (S-video connections are sometimes
called S-VHS connections, but the only link between S-video and S-
VHS is that S-video connections were first introduced on Super
VHS VCRs.)
S-video is most useful when the incoming signal was never in
composite form to begin with. Digital video sources, such as DVD
and DTV, fall into this category. With these sources, and S-video
connection will usually give a significantly better picture than a
composite-video link. But if the luminance and chrominance
elements were combined at some point – as in digital satellite
signals that were delivered to the uplink site as composite video –
using S-video connections later in the signal chain is unlikely to
yield much, if any, noticeable improvement.
Component video takes the process one step further by keeping
the elements that make up the chrominance signal separate as
well. That gives you a luminance signal (Y) and two color-
difference signals, Y – R (luminance minus red) and Y – B
(luminance minus blue). From these three signals, the color
demodulator within the TV set can derive the RGB (red, green, and
blue) signals necessary to drive the display. This can yield another
step up in picture quality with MPEG digital video sources such as
DVD and DTV, for which component video is the native format. A
component (or digital) video connection is necessary for
progressive-scan signals, and a wide-bandwidth component
connection (or a digital connection) is necessary to handle high-
definition signals. Component connections are usually made via
three RCA jacks.
Some high-end sets – front projectors especially – have RGB-
component connections. Typically these consist of five RCA jacks:
three for the color components plus two synchronization signals,
horizontal and vertical (thus the term RGB+H/V). Sometimes
these inputs are switch able between component-video and RGB-
component modes.
For DTV, especially, some manufacturers use other types of
connectors for component-video signals, either 15-pin VGA or
something proprietary. The key is to make sure your TV has the
right inputs to match up with the outputs on your source
components – and enough of them, especially if you’re not using
an external switcher.
Increasingly, HDTV sets and monitors also come with digital video
inputs, either FireWire (a.k.a. IEEE 1394 or i.Link) or, much more
often, DVI (Digital Visual Interface). This is a desirable feature
because it helps ensure compatibility with digital copy-protection
systems that may be applied to future DTV broadcasts and because
it keeps the signal digital all the way to the set’s scaler, instead of
requiring an extra analog-to-digital step that might slightly reduce
the final picture quality.
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