HDMI for High Definition Television





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 Las Vegas in 2003. HDMI accomplishes the task of simplifying the installation by integrating all of the interconnects while simultaneously improving performance. HDTV signals are a significant challenge for distribution. When your service provider distributes the signal, say from a satellite to your home, the signal is compressed to reduce the bandwidth. Once the signal is received by your receiver, the signal is uncompressed. HDMI can handle the signal at full bandwidth, unlike older standards like Firewire.


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 Authorized Testing Center. A 6-foot cable should cost less than $10. Save your money for the items where money actually accomplishes something.


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.










About the Author:


Brian Bradshaw is an InfoComm Certified Technical Specialist (CTS), Microsoft Certified Technology Specialist (MCTS), and CompTIA A+ Computer Technologist. Areas of expertise include Video, HDTV, Audio, Computation, SATCOM Systems, and Communications.

Website: http://bradshaw-vacuum-technology.com/