Wednesday, September 12, 2007

HDTV Video Connections or why is everyone fat on my TV?

We get a few questions on connecting DVI, VGA and component sources, equipment and monitors. In Part I, we will discuss various DVI connection types. Our Part II will look at the popular VGA and component connecting options. Part III will cover scalers/converters for different display configurations, and we will throw in some switching.

Part I


DVI comes in three different formats DVI-D, DVI-A and DVI-I. What are the differences?

DVI-D, which is the most popular, is an all digital video only signal and the predecessor to HDMI. On consumer devices it will have a HDCP(High Definition Copyright Protection) features to prevent non HDCP devices and displays from connecting and copying the signal. This feature requires a handshaking by all equipment to verify that the equipment connected is HDCP. Some earlier monitors designed for computer application are not HDCP compliant. They will work with a computer, but not with set top boxes, DVD players and other DVI consumer electronics that require HDCP compliance. All second-generation HDMI connections are HDCP compliance. Since DVI preceded HDMI it is backward compatible, if the DVI equipment is HDCP compliant. A simple DVI to HDMI adapter or cable can connect HDCP compliant equipment.

DVI-A is an analog display connection only and compatible with VGA. DVI-A to DVI-A only cables are very difficult to find, since the design purpose of DVI was a digital interface. DVI-A to VGA cables are used with some graphic cards and Mac computers that have a dual purpose DVI-I connector, which leads us to the next configuration.

DVI-I is a combination DVI-D and DVI-A connection. You can find these on high-end video cards, frontal projectors, and Apple Mac computers. They are used to save real-estate on the output connection interface. By using a DVI-D/VGA splitter or adapter you can chose either the digital or the analog connection for your specific requirement. This is application dependent.

HDMI is the next generation of DVI and digital only. HDMI has digital sound included in the connection, however when you adapt from DVI to HDMI no audio is passed.

Note when connecting a DVI/HDMI connection to your computer the native computer resolutions available will not be a HD TV’s 720P/1080i format signal, unless your video driver has HDTV outputs resolution settings. There are third part programs like PowerStrip, which are not perfect and require experimentation to match computer output resolutions to HDTV displays. The ultimate solution is an external scaler/converter, which you can program to match the display input requirement, independent of the signal source.

Stay tuned for part III when we discuss scalers.