HDMI (High-Definition Multimedia Interface) is an interface standard used for audiovisual
equipment such as high-definition television and home theatre systems. With 19 wires
wrapped in a single cable that resembles a USB wire, HDMI is able to carry a bandwidth
of 5 Gbps (gigabits per second). This is more than twice the bandwidth needed to
transmit multi-channel audio and video, future-proofing HDMI for some time to come.
This and several other factors make HDMI much more desirable than its predecessors,
component video, S-Video and composite video.
HDMI is an uncompressed, all-digital signal, while the aforementioned interfaces
are all analogue. With an analogue interface, a clean digital source is translated
into less precise analogue, sent to the television, then converted back to a digital
signal to display on screen. At each translation, the digital signal loses integrity,
resulting in some distortion of picture quality. HDMI preserves the source signal,
eliminating analogue conversion to deliver the sharpest, richest picture possible.
Previous video interfaces required separate audio cables, with the vast majority
of people using standard RCA L/R analogue audio jacks. HDMI, with its abundant bandwidth
and speed, carries not only video but also up to eight digital audio channels for
uncompromised surround-sound. It replaces the tangle of wires behind the system
with a single cable, greatly simplifying the entire setup process of the home theatre
system while delivering top tier performance.
Though standard HDMI or "Type A" has 19 wires, "Type B" will
have 29 wires. The latter is targeted for the motion picture industry and other
professional applications. Both varieties are "Intelligent HDMI," referring
to the built-in capability for HDMI-enabled components to talk to each other via
the interface. Auxiliary information can provide all-in-one remote functionality
and other interoperable features not possible in previous interface technologies.
HDMI supports standard video formats, enhanced video and high-definition. It is
also backwards compatible with DVI (Digital Video Interface). High-end graphics
cards featuring a DVI port can connect to a HDMI interface via a DVI/HDMI cable.
This is simply a cable with a DVI connector on one end and a HDMI connector on the
other. As a rule, HDMI cables should not run longer than 15 feet (5 meters), or
degradation of the signal could occur.
As of 2005, many high-end television sets were sold with at least one HDMI interface.
Some experts advise that two HDMI interfaces will provide more flexibility, and
for those who want to connect a game console, three might serve better. Multiple
interfaces will become common on digital TVs as the industry incorporates HDMI interfaces
into more peripheral components.
