| Video Noise July 2002
Digital Video Interfaces:
Where Are We Now?
There’s a lot of talk about digital video interfaces
being the wave of the future. There is no doubt this is true. Many high-definition (HD)
products including video displays, videotape recorders for home use, and perhaps some DVD
players will appear in the 2002-2003 model year with digital video interfaces. Mitsubishi
already has a couple of products on the market with digital interfaces. Digital video
interfaces promise bi-directional communication between components. This may not mean much
to people who aren’t into the technology side of things, so here’s a little
intro to what will be possible.
First, you should understand the difference between digital
video and the normal analog video signals we have been using for decades -- since the dawn
of TV. Analog video contains image information in a signal that changes constantly with
time. Digital video converts that analog signal to a continuous string of numbers. Inside
the video component, those numbers drive the display device in either analog or digital
mode depending on what type of display device it is. If something alters the analog video
signal in any way, there will be an alteration of what you see on the screen.
Interference, snow, or ghosts all come from the analog video signal being distorted in
some way compared to the original broadcast signal.
If the digital signal is hit with the same problems, video
quality is not changed in any way as long as the video product can interpret the numbers.
Even if the digital signal is severely damaged, making some of the numbers impossible to
interpret, powerful coding within the digital signal allows video products to determine
what number was supposed to exist where the damaged number was. The damaged number
is simply replaced with the correct number.
Digital video signals tend to be all or nothing, meaning
you either get a perfect picture or no picture at all. Analog video signals are better the
closer you are to the broadcast antenna where the signal is stronger and less apt to be
damaged by external variables. However, large antennas can make up for being farther from
an analog video signal -- the larger the antenna, the better the picture. For digital
video, if you are getting a stable image, adding a larger antenna won’t improve the
picture.
The best video connection in home use today is component
video. This connection requires three separate cables that can be pricey if you choose to
go for a better-quality cable set. A digital-video-interface cable will have several wires
in a single cable and should cost much less than a high-end component-video cable set. The
RCA connectors on component-video cables were not originally intended to be used with
video signals because the RCA jacks are not true 75-ohm connectors. Digital video
interfaces should eliminate the cable- and connector-impedance issues, which should make
signal transmission better.
Today, you have to tell your DVD player what kind of video
display is connected. This is an easy thing for some people but doggedly confusing for
others. With bi-directional communication, your TV will tell the DVD player its
capabilities each time it is turned on. That will be one less thing for the owner to worry
about. It will even be possible for DVD players or their HD optical-disc successor to tell
your video display what mode to use for the disc being played. The disc player will get
information from the disc being played regarding what modes are available on it and tell
the video display what mode to use for that particular disc.
Audio and video could travel on the same cable cutting the
number and cost of cables. Disc players could communicate directly with the surround
processor or receiver even if the two are not connected directly. The disc player and
surround processor or receiver will then be able to negotiate which soundtrack on the disc
to use -- all done going through the video display. Once the receiver or surround
processor knows how many and what size speakers are connected, the user of the system will
rarely ever have to make any choices about which soundtrack to use. Can you imagine a
home-theater system with only two interconnect cables replacing all the audio and video
cables needed today? Mere mortals may actually be able to connect a home-theater system
without help.
Digital video and new components
With all the potential benefits of the digital interface,
if you are considering purchasing a new high-definition display or tape machine this year,
you should then demand a digital video interface be present, right? Maybe not. Here’s
why.
There are actually four digital video interfaces trying to
become the standard in the market right now. One is IEEE-1394, also known as FireWire or
iLink. The other is called Digital Video Interface or Digital Visual Interface;
DVI for short. There are issues with both systems. IEEE-1394 may not have all the
capabilities the industry ultimately wants, so it is subject to being changed in the
future. DVI is an existing standard for digital video used with computer systems. But for
the home-theater user, there are three competing versions of DVI that are not compatible
with each other. How would you know which one your product has, let alone which version it
should have to be compatible five years from now?
The bottom line for consumers today is that digital video
interfaces are not fully sorted out. There is no final standard and anything you buy today
may never do more than allow a single manufacturer’s display, tape players, disc
players, and processors to work together. That limits your choices considerably and makes
digital video interfaces on home-theater components something less than a guarantee of
future compatibility.
What should you be concerned about if considering
home-theater components today? Think of what you buy today as being useful for up to 10
years depending on how overcome by the need for new features and capabilities you have
been in the past. Personally, I find that I must have a new DVD player about every
18 to 20 months to keep up with developments. That puts some perspective on how much
I’m willing to spend on a DVD player. Likewise, getting into an HD monitor today with
the limited programming available means you may want to consider tempering the purchase
just a bit. Don’t avoid the purchase, but go for something you won’t feel bad
about upgrading five or six years from now. It’s going to take that long for the
digital-video-interface wars to be completely sorted out anyway. In the meantime, the
analog inputs/outputs for your HD display, HD tape, or HD disc system will still perform
their job well -- even if you aren’t "digital" yet. HD components for years
to come will be equipped with analog outputs to maintain compatibility with existing
equipment.
My advice is not to worry too much about the
digital-video-interface question yet. There are just too many variables and too much
development time that will pass before the system is fully debugged and universally
compatible. If you are ready for an HD display, HD videotape machine, or HD cable or
satellite decoder, find a good one that fits your budget and go for it. HD is here and
it’s great -- if still somewhat limited. If you feel it’s time to stop waiting,
don’t let the digital-video-interface issue freeze you in your tracks. On the other
hand, expensive HD products that are serious budget stretchers are best avoided if you are
on the typical working stiff’s household budget.
...Doug Blackburn
db@hometheatersound.com |
