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HOME REVIEWS CONTACT ABOUT January 14, 2010
HDMI
for High Definition Television
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HDMI (High-Definition Multimedia Interface) is now the
standard digital audio-video cable for HDTV.
HDMI was first demonstrated at Consumer Electronics Show (CES) in
HDMI is an
industry-supported specification. It is
not a proprietary specification that one manufacturer is trying to force on the
market. The industry needed a quality digital connection standard, and consumer
electronics manufacturers decided to create a standard that would benefit both
the industry and the consumer
DVI Heritage
A DVI connection offers comparable performance to
HDMI. In fact, HDMI is built on the DVI
standard. However, DVI became problematic
because a strict interface standard was not maintained. HDMI should ensure that equipment
compatibility is maintained. The HDMI
connector is backwardly compatible with the existing DVI video input that is
used on most PC video cards. The HDMI cable
integrates all of the video signals, as opposed to component video where each
of the RGB (red, green, black) signals has its own cable. Older interconnect techniques like S-Video or
component video, require audio signals to be handled separately, and the
performance is somewhat worse than HDMI.
Interoperability can be an issue with
standards like HDMI. Most of these
problems come about by improper implementations of the technology. When there
have been problems, the HDMI standards group has required that the issue be
resolved. Some products have been recalled.
An exception are some set-top boxes used by
some local cable TV companies. Some of
the boxes have compatibility problems that the cable companies have been
unwilling to resolve.
HDMI Technical Specifications
HDMI allows for 2-way communication between components, so
that, for example, your HDTV can tell your signal source whether the picture is
16:9 or 4:3. HDMI integrates remote
control so that all HDMI compatible modules can be controlled with a single
remote control. Push the play button for
your Blu-Ray DVD player, and not only will the DVD start, but the HDTV, and
audio components will automatically turn on.
The standard used by HDMI is called "Consumer Electronics
Control" (CEC). Companies have
their own trade names for CEC. Examples
are "Anynet" from Samsung, "BRAVIA
Theatre Sync" from Sony, "Kuro Link"
from Pioneer, "EasyLink" from Philips, and
"NetCommand for HDMI" from Mitsubishi. All HDMI devices should be intercompatible.
High-bandwidth Digital Content Protection (HDCP) is the
software protection scheme that is included with HDMI interfaces to prevent
unauthorized copying of protected material.
This can sometimes create problems with compatibility, but HDCP is a
necessary evil. As more content is delivered
digitally, the content producers are increasingly concerned with piracy because
the content can be perfectly duplicated.
Without copyright protection, content producers like movie studios would
be unwilling to distribute their product.
Most programming will only deliver full resolution on HDCP protected
outputs.
Most currently available HDTV sets have two or more HDMI
inputs so that different signals from your HDTV service provider (i.e.
satellite system), Blu-ray DVD player, game console, and/or computer can be
connected. If you are now selecting your
HDTV set, note the number of HDMI inputs, and consider how many inputs you may
need in the future. If your set does not
have enough inputs, you may have to add a HDMI Switcher to you system. Figure on spending about $100.
Also integrated with HDMI are the audio signals. HDMI can handle eight channels of 24-bit
audio at 192 kHz, enough for a 7.1 surround-sound
system. This is needed for surround sound programming
such as Dolby TrueHD and audiophile programming such
as DTS-HD Master Audio. A Dolby TrueHD bit stream can carry up to 14 discrete sound
channels. DTS-HD Master Audio delivers
audio at the very high rate of 24.5 mega-bits per second (Mbps) on a Blu-ray
DVD. In addition, DTS-HD Master Audio offers 7.1 audio channels at 96k sampling
frequency/24 bit depths.
HDMI is compatible with HDTV signals up to 1080p
resolution, a bandwidth of about 2.6 Gbps.
HDMI is capable of a bandwidth of up to 5 Gbps.
There are multiple versions of HDMI cables. In addition the standard Type “A” connector,
there is a "Mini-HDMI" (Type "C"), which is exactly what it
sounds like: a miniaturized version for use with small peripherals like a
camcorder. A special cable with a small
connector on one end and a conventional type “A” HDMI connector on the other
end is needed. Another version is
"HDMI 1.3", which is supposed to be an enhanced version of HDMI capable
of "deep purple". According
the HDMI association, 98 percent of currently sold HDMI cables are compatible
with HDMI 1.3.
HDMI cable length is an important consideration. Anything over 30 feet has the potential for
causing significant degradation of the signal, but cable lengths of 75 feet or
less will be OK in most circumstances.
There is not a significant difference between expensive cables ($50 or
more) and the inexpensive cables found at your discount retailer, or better yet
from an on-line retailer like Amazon.com.
Any cable marked with the HDMI logo must have been tested
at an
HDMI has become the de facto standard for HDTV
interconnects. Even though some of the
features of HDMI are probably not implemented fully on your current equipment,
once you upgrade, HDMI will most likely support the interconnect needs, at
least for the foreseeable future.