By Bob Gatton
This is the third and final of the audio and video connection articles, and it will focus on digital video connections. (I know, I know: Finally!) There are only two types of consumer digital video connections: DVI (digital visual interface) and HDMI (high definition multimedia interface). There also is a DVI analog interface, but this connection is used so rarely that we're not going to bother discussing it.
Both DVI and HDMI can deliver a great picture, but the HDMI has higher bandwidth, which means that it has the capacity to deliver a signal that is higher quality than the best of today's HDTV standards.
The DVI cable was originally developed for connecting computers to digital monitors and projectors. Later it was adopted by the audio video industry. The original specification was for a maximum distance for a DVI cable of 5 meters, or about 16 feet, but many manufacturers have made longer cables that work very well.
If a really long cable is needed – as long as 300 feet – the signal can be converted from electrical to optical. Repeaters also can boost the signal.
HDMI was introduced after DVI. It added audio and as many as to eight channels, the plug is smaller, and it needs just one connection for both audio and video. Furthermore pieces of HDMI equipment can "talk" to each other. For instance, a DVD player connected to a television via an HDMI cable can tell the television what aspect ratio is best for the movie.
Manufacturers are dropping DVI connections in favor of HDMI as new models are introduced. To make the transition easier, cable makers sell cables that have a DVI connector on one end and a HDMI plug on the other end. If you use one of these cables, be sure to connect the audio separately. Remember that the DVI connection does not carry the audio signal.
I'm going to throw one last acronym at you: HDCP, which stands for high bandwidth digital content protection. To watch some programming at the best possible quality, both the source and the display need to be HDCP-compatible. Producers of movies and other programming want to protect their copyrights, and HDCP is a system that lets you watch high-definition programming but blocks unauthorized duplication of copyrighted material. There are flags in the content that tells the display that it is okay to watch but may or may not let you record the program.
All HDMI equipment and most DVI equipment support this standard. If a piece of DVI equipment supports HDCP, the specification sheet will say something like DVI/HDCP compatible or DVI with HDCP.
If HDMI has capacity that is higher than even the best of today's HDTV signals and only one cable is needed for both audio and video, why are there composite, component, S video, analog audio and digital audio connections? The answer is that it will take more than a few years for all AV equipment to have digital connections. Even if you have a new high-definition television, you probably still want to connect your old VCR, and these connections let you do so without forcing you to rush out and buy yet another new piece of equipment.
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