What is an HDMI cable and Why do I Want One?

An HDMI cable is a cable that connects two devices using the relatively new, high definition multimedia interface (HDMI). This interface is still relatively uncommon but is beginning to be seen in HDTV sets and other home theater equipment.

One of the advantages of an HDMI cable is that it can carry HDTV video signals and 8-channel digital audio in one cable, and still has bandwidth to spare. This means that you can have just one cable running, for example, from your HDTV cable or satellite box to a home theater receiver.

As with everything on the cutting edge of technology, its not quite as simple and straightforward as it sounds. There are two types of HDMI, Type A, which is a 19-pin connector and can carry HDTV at up to 1080i resolution, and a new on called Type B, which is a 29-pin connector that uses two discrete channels to transfer HDTV at higher resolution than 1080i.

The Type-A HDMI cable is compatible with DVi (digital video interface) connectors, so you can use an adaptor to connect a tuner with a DVI ioutput to a TV with HDMI, or vice versa.

HDMI connectors are typically found on HDTV equipment, however some newer DVD players also have them. In this case, a chip inside the DVD player 'up-converts' the 480i or 480p signal from the DVD to either 720p or 1080i, depending on the HDTVs native resolution. The signal is then passed digitally over the HDMI cable to the HDTV, without the need for any digital-analog-digital conversion.

The HDMI standard includes something called HDCP (High-bandwidth Digital Content Protection), and anti-piracy measure developed by Intel. All equipment that has an HDMI interface must support HDCP. Whenever a signal is sent from one HDMI connector to another, a code is embedded in the signal which must be de-coded by the receiving equipment in order for the signal to be processed. If either of the pieces of equipment doesn't support HDCP, they won't be able to communicate.

HDMI sounds like a great piece of technology, although the copy protection is bound to irritate some users. However, it's not necessarily the best choice for connecting your home theater kit. To find out more about whether you should go for digital or analog connectors read our guide: HDMI or Component Video?

DVI to HDMI Adapter