In December 2002, an industry consortium of cable multiple system operators and consumer electronics manufacturers sent a Memorandum of Understanding (MOU) to the FCC detailing their plans to implement DTV / HDTV cable systems and related hardware. In this MOU, there was a specific time table to rollout a new generation of displays that feature digital video inputs with HDCP:
480i grade televisions - none.
480p grade televisions - as follows (either DVI or HDMI with HDCP), or 480P Y,Pb,Pr (analog) interfaces:
o With screen sizes 36 inches and above -- 50% of a manufacturer's models offered for sale effective July 1, 2004 ; 100% of such models effective July 1,2005 .
o With screen sizes 32 to 35 inches -- 50% of a manufacturer's models offered for sale effective July 1, 2005 ; 100% of such models effective July 1, 2006 .
720p/1080i (HDTV) grade televisions - as follows (either DVI or HDMI interfaces with HDCP):
o With screen sizes 36 inches and above -- 50% of a manufacturer's models offered for sale effective July 1, 2004 ; 100% of such models effective July 1,2005 .
o With screen sizes 25 to 35 inches -- 50% of a manufacturer's models offered for sale effective July 1, 2005 ; 100% of such models effective July 1, 2006 .
o With screen sizes 13 to 24 inches - 100% of a manufacturer's models offered for sale effective July 1, 2007 .
[cablesnake] Interconnections:
In order to allow sources and displays to work, they must be interconnected, usually with cables of some sort. This sounds simple enough, yet this is the area where most customer installation problems take place. Today, a typical home theater system can cost anywhere from a few thousand to tens of thousands of dollars, or more. Despite the fact that these figures represent a major investment for most end users, typically less than 3% of the total system price is spent on interconnection cables.
It is a regrettable fact that for most people a cable is just that - a cable. However, when you consider that imperfections in these signal "pipelines" can seriously degrade picture quality, cables start to take on a more profound role. Nowhere is this truer than with the DVI and HDMI cables needed to support digital HDTV.
While audiophiles may argue the complex dynamics of ultra-high fidelity esoteric speaker cables, these cables must carry relatively low frequencies, most of which are below 20 kHz. However, with DVI and HDMI signals, data rates of up to 1.65 Gbit/sec. are possible. In the analog world this would be equivalent to 165 MHz which is more than 8,000 times higher frequency than most audio signals. For short cable runs of less than 5 meters (16.4 ft.) there are usually not too many issues; however, these high frequencies pose serious challenges for longer length DVI and HDMI cables. In general, the higher the frequencies and the longer the cable length, the greater the likelihood that image problems will occur. For example, at low resolutions a DVI signal might travel 20 meters without signal degradation, but at higher resolutions the same cable could exhibit significant image degradation. For this reason, cable lengths for higher resolution signals, such as 1080p, are usually limited to 10 meters or less. Figure 1 illustrates this problem:
[HDTVimagequality]
> Image of 800x600 screen with a conventional 20 meter DVI cable Image of 1600x1200 screen with same 20 meter of DVI cable
To solve the issue of long digital cable runs and reap the full benefits of improved picture quality, cable manufacturers have made various attempts to improve their cables with mixed results.
Here are some key points to look for:
*
Does the manufacturer offer high resolution, long length DVI or HDMI cables ? Standard cables usually use 28-gauge or 30-gauge wire. High quality DVI and HDMI cables should use 24-gauge or 22-gauge wire. The heavier wire gauge helps avoid some of the high frequency attenuation that long cables suffer.
*
Does the cable use silver plated wires for the high speed TMDS data lines (the wires that actually carry the digital picture content)? At very high frequencies, the signal does not travel through the copper wire; it travels on the surface. The silver plating helps mitigate what are known as "skin effect" losses and limits the insertion loss (i.e. less high frequency attenuation).
*
Does the manufacturer rely on highly embellished claims that sound more like science fiction than science fact? Do they provide a guaranteed level of performance? More than just a money back guarantee, does the manufacturer make a pledge of performance? If yes, this helps make sure you choose the right cable the first time and avoid hassles with returning substandard products.
*
What warranty does the manufacturer offer?
*
What level of support does the manufacturer offer? If you have a problem or an installation question, can you get fast, reliable answers?
These are just some of the important questions that must be answered when designing and installing a new HDTV display system. For more sophisticated systems, you may want to rely on a professional home theater designer and installer. CEDIA (Custom Electronic Design and Installation Association) is an excellent resource for both end-users as well as home theater professionals. You can learn more about CEDIA at: http://www.cedia.net/whatis_cedia/
Whether you decide to "do-it-yourself" or contract a professional, having deeper insight into HDTV's past and present will only serve to further enhance your own HD experience. In Part II of this article, we'll take a closer look at the trends and technology that are shaping tomorrow's HDTV systems - and focus on why these factors are important considerations for today's buyers.
