Today's high-definition home theaters run on digital audio and video, and HDMI™ is the connection of choice. That's because HDMI (High-Definition Multimedia Interface) delivers crystal-clear digital video and audio via a single cable, dramatically simplifying cabling and helping A/V fans enjoy the best possible home theater experience.

In this article, we'll explain what HDMI is and how it differs from conventional analog connections, and include some quick tips on choosing HDMI cables. You'll also learn what the exact differences are among the evolving versions of HDMI. And finally, we'll look at some real-world HDMI hookup issues along with solutions and workarounds.

HDMI: The "king" of high-quality connections

HDMI's pure-digital interface is the best way to connect high-resolution components — like upconverting DVD players, Blu-ray Disc™ players, the PlayStation® 3 and Xbox 360™ game consoles, and some HD-capable satellite and cable TV set-top boxes — to HDMI-equipped high-definition TVs. And increasingly, devices that are inserted between the source components and the TV — like home theater receivers and video switchers — also include HDMI connections.

Increasingly, home theater fans find HDMI to be the best way to connect components to HDTVs.

Of course, HDMI isn't the first digital video connection for home theater — that distinction belongs to DVI. But DVI, a video-only interface, was originally developed for computer use, while HDMI was designed from the ground up for use with home audio/video gear. Thanks to its superior capacity, versatility, and ease of use, HDMI has largely replaced DVI in home theater equipment.

Single-cable convenience, plus so much more

The ability to send high-definition video and multichannel audio over a single cable is unique to HDMI, but this interface offers other big advantages. A standard HDMI connector has 19 pins, which carry not only audio and video data, but also 2-way control and identification information, and even low-voltage power. HDMI provides maximum signal integrity and a secure, "smart" link between devices — it's one of the best ways to "future-proof" your system. Here are two more reasons to look for HDMI when upgrading your gear:

• Superb picture and sound quality: HDMI connections keep audio and video signals in the digital language of 1s and 0s, eliminating the compromised picture and sound quality caused by digital-to-analog conversions and reconversions. HDMI supports video resolutions up to 1080p, which is key for the new 1080p-capable HDTVs and high-definition disc players. Although there are a few TVs that accept 1080p signals via DVI or component video, it's nearly impossible to find a high-def source that can supply 1080p over anything besides HDMI. And HDMI's sound capability now supports up to 8 channels of super-high-quality 24-bit 192kHz audio.
• Industrial-strength copy protection: This probably seems like more of a benefit for content owners like movie studios than for consumers, but it directly affects the quantity and quality of what we can watch — now, and in the coming years. HDMI's wide adoption is due in large part to Hollywood's demands for ever-stronger copy protection measures to prevent piracy. HDCP (High-bandwidth Digital Content Protection) is present on virtually all HDMI-equipped devices even though it's not officially part of the HDMI spec. Without HDCP, both the quantity and quality of high-def content available to consumers would almost certainly be more limited than it is.
  However, HDCP also has a downside. One of its main jobs is to "authenticate" the connection between two components via a "digital handshake," and problems with this handshake process can result in the loss or degradation of picture and sound.

Quick tips for choosing HDMI cables

Some components include an HDMI cable in the box, but most don't, so you'll need one to connect your gear for the best picture and sound. You won't see dramatic differences in picture quality among HDMI cables. Unlike analog video transmission, which can display varying degrees of picture quality, digital video transmission typically delivers a clean, clear picture or no picture at all. But you'll still want to choose a high-quality HDMI cable, especially for longer lengths or in-wall installations. Different cables use different materials and construction techniques, and some are rated by the manufacturer to maintain maximum signal quality over longer cable lengths. Some users have encountered interoperability issues when making HDMI connections, but these are almost never the fault of the cable itself.

Before an HDMI cable can carry the HDMI logo, it must be tested at an HDMI Authorized Testing Center. The tolerances for HDMI cables are incredibly tight: the length of each strand of wire must be within 1/20,000th of an inch to ensure it will work properly.

On the next page, we'll cover some slightly more technical aspects of the HDMI interface and describe the differences among the various versions of HDMI.

An evolving standard

In this fast-changing era of new formats and technologies, HDMI is the accepted universal connector for digital home entertainment. The HDMI spec was developed by a group of companies including Hitachi, Matsushita (Panasonic), Philips, Silicon Image, Sony, Thomson (RCA), and Toshiba. It's also supported by movie studios like Fox, Universal, Warner Bros., and Disney, as well as satellite providers DIRECTV® and DISH™ Network, and CableLabs® (an R&D consortium that develops new technologies for cable TV operators). Over 800 companies currently build HDMI-equipped products.

Many new TVs have two or more HDMI inputs. The lower input includes stereo audio jacks for backward compatibility with DVI-equipped video components.

The HDMI standard continues to evolve to meet the needs of high-performance home theater equipment. All versions of HDMI are backward compatible with previous versions, as well as with DVI (however, a DVI connection passes video only, not audio). Part of the built-in intelligence of HDMI enables it to automatically send the highest quality video and audio formats that are mutually supported. In other words, if you connect two devices, one with HDMI version 1.1 and the other with 1.2, the system will be limited to the 1.1 feature set.

Although you'll often see the HDMI version listed as part of a component's specifications, it's probably best not to pay much attention to it. For specific details about a particular component's audio and video capabilities, you're better off focusing on the component's feature list. A product's HDMI version by itself doesn't mean that all the latest features have been implemented; it does not guarantee a particular feature set. The reason is that the capabilities listed for each version of HDMI are optional, not mandatory.

It's up to each manufacturer to decide which HDMI features to build into its gear. A perfect example is 1080p video input capability. Although the original HDMI 1.0 spec included 1080p video (before 1080p TVs even existed!), it wasn't until 2006 that a significant number of HDTVs included 1080p-capable HDMI inputs.

Do I need to worry about compatibility between HDMI versions?
Although there have been multiple versions of the HDMI spec, there haven't been any physical changes to the HDMI connectors on cables and components. That means you don't have to worry about buying a cable that's "rated" for a particular HDMI version. Plus, each new HDMI version is backwards compatible with older versions, so your older and newer HDMI-equipped components can generally still work together.

So what are the differences between different HDMI versions? Take a look at our summary of HDMI's evolution below:

• HDMI 1.0: The original spec called for a single-cable digital audio/video connection with 165MHz bandwidth and a maximum bitrate of 4.9Gbps (enough for 1080p video). Two-channel audio only. Released December, 2002.
• HDMI 1.1: Added multichannnel audio support for DVD-Audio (up to 5.1 channels). Released May, 2004.
• HDMI 1.2: Added support for multichannel one-bit audio formats like SACD (Super Audio CD). Included support for HDMI connectors on personal computers. Required displays with HDMI 1.2 or later to support future low-voltage devices. Released August, 2005.
• HDMI 1.2a: Fully specified the Consumer Electronic Control (CEC) features and command sets for remote control functions. Required cable manufacturers to submit longer cable lengths for additional testing for spec compliance. For a device to pass 1.2a testing, all of its HDMI connectors required inspection and approval by HDMI Licensing, LLC. Released December, 2005.
• HDMI 1.3: Increased bandwidth to 340MHz and the maximum bitrate to 10.2 Gbps (plus the capability for higher bandwidth in the future). Adopted the "Deep Color" standard, which supports 10-bit, 12-bit, and 16-bit color for over one billion possible colors — previous versions were limited to 8-bit. (Note: Because color information is based on three primary colors — red, green and blue — you'll sometimes see 1.3's enhanced color depth described as 30-bit, 36-bit, and 48-bit.) Added support for the "xvYCC" extended-gamut color space standard (also known as x.v.Color), which supports 1.8 times as many colors as existing HDTV signals. (No commercially available video content currently uses Deep Color or x.v.Color.) Added ability to output new lossless compressed digital audio formats (Dolby® TrueHD and DTS-HD Master Audio™) for decoding by a compatible A/V receiver. Incorporated automatic "lip sync" control for perfect audio/video timing (sometimes an issue when audio is sent to a surround receiver or processor and video is delivered directly to the display). Also made available a new mini-connector for use with smaller devices such as digital cameras and camcorders. Released June, 2006.
  The 1.3 spec has been recently updated to 1.3a, followed by 1.3b. However, for consumers, there is no difference between versions 1.3, 1.3a or 1.3b. These are minor revisions that relate to manufacturing and testing issues and do not affect features or functionality.

On the next page, we'll talk about some common HDMI-related hookup problems and solutions.

HDMI connection issues, solutions and workarounds

If your TV only has one HDMI input, consider upgrading your home theater receiver to one with HDMI switching for multiple components.

While different HDMI versions may cause some of the interoperability issues experienced by consumers, most of the problems are caused by a manufacturer's improper or incomplete implementation of the technology. Some incompatibilities in the digital "handshake" of the HDCP copy-protection code still exist between HDMI-connected components, especially when routed through an HDMI-equipped home theater receiver. Whenever problems like these are discovered, the HDMI standards group contacts the manufacturer and requires that the issue be resolved. In some cases, products have been recalled.

Beyond the initial handshake, there are other possibilities for miscommunication between components. At the beginning of the article, I mentioned that HDMI supports two-way communication between a video source and a TV. Part of that digital conversation is known as "EDID" (Extended Display Identification Data), which describes the TV's capabilities to the source component. EDID info typically includes the manufacturer name, product type, screen resolution, and color depth. Thanks to EDID, two devices can not only talk to each other, they'll actually know whom they're talking to. And that makes auto-configuration possible, which simplifies your setup process.

Keeping all that in mind, here are some of the most common HDMI connectivity issues we've heard about from customers, along with possible solutions or workarounds:

No picture or sound using HDMI from DVD player to TV
Some video components come from the factory with the HDMI output set to "off." You can switch it to "on" via the player's setup menu, or sometimes by pressing the "HDMI" button on the component's front panel or remote.

No sound when using the HDTV's HDMI input
Most TVs lack built-in decoding for Dolby Digital and DTS surround sound, and can only play 2-channel audio. But many HDMI-equipped video components come from the factory set up to send multichannel audio. Usually, just changing the component's audio setting to "2-channel (PCM)" solves the problem.

No picture when connecting a cable box to an HDTV
This is usually the fault of the cable box, as many local cable providers have still not upgraded their customers' equipment with new firmware or new boxes to make them fully compliant and compatible with HDMI-equipped TVs and A/V receivers. Customers should report problems to their local cable providers. As with most HDMI-related connectivity issues, one effective workaround is to use component video connections and optical or coaxial digital audio connections.

No closed captions displayed when using HDMI connections
Unfortunately, the HDMI spec doesn't include any requirement for carrying closed captioning data. So, if you connect a video component like an HD cable or satellite receiver or DVD/Blu-ray player to your HDTV using HDMI, you won't see conventional closed captions. If you need to view closed captions from your cable or satellite box, use a component video connection — the closed captions will pass through and you'll still enjoy a high-def picture.

A related issue is that many DVDs and Blu-ray discs simply aren't encoded with closed captioning data. However, most discs are encoded with subtitles, which are similar to closed captions, and subtitles are compatible with HDMI. In fact, a growing number of content providers are using a particular type of subtitling called "Subtitling for Deaf and Hard of Hearing," which is optimized for people with hearing disabilities. While not all discs include subtitles, virtually all DVD and Blu-ray players are capable of decoding subtitles if they're present.

Can't get multichannel audio with an A/V receiver connected between the video source and an HDTV
We've mentioned HDMI's intelligent two-way communication between components, but sometimes it actually contributes to hookup problems. Normally, the display tells the source device about its video and audio capabilities. Virtually all TVs are limited to 2-channel audio playback. Since many A/V receivers employ a "repeater" type of HDMI switch, the receiver simply passes the 2-channel information to the source, despite the receiver's multichannel capabilities. So, the player sends only 2-channel audio to the receiver, rather than high-quality surround sound.

Solving this type of HDMI interoperability issue requires sophisticated technology, like this video switcher/processor from Key Digital. Now, one handy workaround would be to simply run a separate optical or coaxial cable for audio. Unfortunately, many HDMI-equipped components are designed to turn off digital audio outputs when the HDMI output is in use. We have found that some models do this and some don't (even from the same brand), and going forward, we expect to see more models switching off their digital audio outputs.

Another receiver-related HDMI sound issue is that some receivers aren't designed to pass audio through their HDMI connections — they perform video switching only. To get multichannel audio from these receivers, you need to connect an optical or coaxial digital cable from your video source to the receiver. Only a few entry-level receivers still have this limitation, but it's something to be aware of.

Plug into the future

HDMI isn't just nice to have, it's now essential to maximize your home theater's performance. You may have noticed that upconverting DVD players limit the resolution on the component video output to 480p — if you want 720p or 1080i/p, it's only available via HDMI.

When high-definition discs launched, it initially appeared that HD-quality signals would only be available from a player's HDMI output (the signal available from the component video outputs would be "down-rezzed" to slightly-better-than-DVD quality to discourage piracy). Millions of owners of non-HDMI-equipped TVs got a reprieve when the studios decided not to activate this "feature" at that time. But some in the movie industry predict that this down-rez flag could begin appearing on high-definition discs beginning in 2010 or 2012. And there is no legal way to convert the digital signal from a high-definition source to an analog component video signal to send to a non-HDMI HDTV.

The bottom line is that if your equipment doesn't include HDMI connections, at some point you will miss out on the best-quality picture and sound available. If you've seen the amazing picture quality available from top-notch DVD players and high-def disc players, you know you could be missing a lot.