Expert Interview: The Basics of HDMI
To many consumers, HDMI is yet another random connection built into the rear panels of A/V devices. In this Q&A, Electronic House Editor-in-Chief Cindy Davis discusses the ins and outs of HDMI with Steve Venuti, Director of Marketing for HDMI Licensing LLC. After reading this, those HDMI connectors carved into your gear will finally make sense.
Cindy Davis: Let's start with a general question: What are the benefits of HDMI to the consumer?
Steve Venuti: First, let me describe HDMI as succinctly as possible. The key benefits are evident in the description:
HDMI (High-Definition Multimedia Interface) is the first and only industry-supported, uncompressed, all-digital audio/video interface. By delivering crystal-clear, all-digital audio and video via a single cable, HDMI dramatically simplifies cabling and helps provide consumers with the highest-quality home theater experience. HDMI provides an interface between any audio/video source, such as a set-top box, DVD player, or A/V receiver and an audio and/or video monitor, such as a digital television (DTV), over a single cable.
There are two main benefits that I would pull out of that overall description of HDMI.
HDMI is an all-digital, uncompressed interface. What that means is that the audio and video signal remains in its purest state from the source to the display. And since it's not converted from digital to analog and back again, and since it's not compressed, this means that the consumer gets the highest quality signal possible and a future-proof technology that has no dependency on compression schemes like MPEG.
HDMI provides this over a single cable. To the consumer, that means an end to the cable confusion and clutter that lies behind just about every home theater system. The following picture illustrates how cabling can be simplified by using HDMI.
One other point that I'd emphasize in the overall description is the term "industry-supported." This is not a proprietary solution that one manufacturer is trying to push on the market. The industry needed a state-of-the-art digital connection standard, and major consumer electronics manufacturers got together to create a standard that would benefit the industry and the consumer (the HDMI founders include Hitachi, Panasonic, Philips, Sony, Thomson (RCA), Toshiba, and Silicon Image). As of today, there are more than 400 companies that have adopted the HDMI standard and are building HDMI into their products.
In addition, because HDMI is all digital, consumers will see a whole set of benefits that just are not possible with an analog connection. I would liken it to the mobile phone industry. When we first had analog cell phones, we were so happy to be able to make a call from just about anywhere. But now, with mobile phones going digital, there are so many more features that are available to us, all due to the fact that the signal is digital. We will see this kind of two-way communication and data sharing in our home theaters, and all of it will happen over digital connections.
CD: Should consumers pay attention to the different versions of HDMI?
SV: It is true that many consumers are confused by different versions of HDMI, but this is something that consumers should really not worry about. I advise consumers to never focus on the specific version of HDMI, but rather, on the feature set of the device, such as 1080p capability, DVD-Audio support, etc.
In fact, looking for the version of HDMI supported in a product does not mean that all the latest features possible from the specification are actually implemented in the product. So again, the key is for consumers to seek the feature, not the specification.
Since we are in a stage of incredible technical innovation in home theater equipment, HDMI also evolves to support new technologies. HDMI 1.0 was launched in December 2002, and since then, HDMI has added capabilities ahead of the market so that when components come out with specific new functionalities, the HDMI connection can support that new functionality.
CD: What about compatibility with older versions of HDMI?
SV: All versions of HDMI are backward compatible with previous versions as well as with DVI, so in no case will consumers experience one version of HDMI that is incompatible with another. HDMI is designed so that devices will automatically send the highest quality audio & video formats that are mutually supported, so this backward compatibility is done with a seamless intelligence that makes it easy for the consumer.
CD: BUT, what if I have an HDTV with HDMI v1, and the new DVD player or set-top box I just purchased is 1.3, will I still get whatever benefits are offered in 1.3?
SV: Let's say you have an HDTV with version 1.1. Let's also say you purchase a new Blu-ray DVD player that has HDMI 1.3 in it.
Now, let's take one specific example of a difference between HDMI 1.1 and 1.3: audio formats. HDMI 1.3 adds additional support for new, lossless compressed digital audio formats Dolby(r) TrueHD and DTS-HD Master Audio.
Okay, let's assume you have an HDTV that has Dolby 5.1 audio, but your new DVD player has newer audio capabilities. Will your HDTV be able to accept the new audio format? The answer is "no." Why? Because the HDTV does not support this new format. The lack of audio features comes from the HDTV, not the HDMI link.
I really think consumers need to ignore the "versions" of HDMI. Newer version of HDMI "support" new technologies, so that when you buy your new source devices -- or new displays -- and hook them all up together, the new features will be supported. But if these features are not part of the original equipment,the original equipment will never be able to offer these features, no matter what connection.
Here's an analogy that might help tie it together:
Imagine I buy a 1995 car. It can go a max of 100mph and freeways at the time are designed to handle cars up to 150mph. So, when I drive my car, I happily max it out at 100mph on the freeway.
Now, 10 years later, I buy a 2005 car. It can go a maximum speed of 150mph and has this cool new feature called "curve stabilization." Well, knowing that this new feature was coming up, the Dept of Transportation started building freeways to support "curve stabilization" around 2003. I take my 2005 car out on one of these new freeways, and I can go 150mph and wow, I can really tear around the curves with that new "curve stabilization" feature.
Now, I get my old car out and take it on a drive on one of these new freeways. I can still only go 100mph (that's all my old car car do) and I don't get that great new "curve stabilization" feature, even though the highway supports it. The reason: my 1995 car doesn't have "curve stabilization" built into its design.
When we carry over this analogy, HDMI is the highway. All new versions of HDMI work with all older versions (as well as DVI), just as the "curve stabilization" highway works with all vehicles that have this feature and all vehicles that don't. HDMI supports every new feature that comes along, and in fact, supports the features well ahead of anyone seeing these features in the market. But, if you buy one component with a new feature, and have an older component without that feature, HDMI, as the transport, cannot make up for the older component's lack of the feature.
That's why we tell people that HDMI supports every feature that's out there. Consumers shouldn't focus on the version of HDMI in the component, they should instead focus on the features of the component.
CD: What should consumers know about HDMI cables?
SV: To consumers, perhaps the most tangible move from an analog connection to a digital one is the physical cable itself. After all, the complicated technology that is happening inside the DVD or HDTV is invisible to all but the engineers who design these systems. So what is there to know about an HDMI cable that is any different from what we know about analog cables? Lots!
The tolerances for HDMI cables are incredibly tight. Because a digital signal is comprised of 1s and 0s, sent over four channels with 19 pins inside the cable, and because these 1s and 0s need to start and end at the exact same time, the manufacturing tolerances for cables are very high. It's for that reason that cables must be tested at an HDMI Authorized Testing Center before they can be marked with the HDMI logo. It also why it is impractical (if not impossible) to splice and crimp an HDMI cable at home (you would need to cut each strand within 1/20,000th of an inch to ensure that it would work).
Fatter cables do not necessarily mean better signals. Previously, fat cables were deemed superior because the copper was thicker and the cables carried more shielding. Additional shielding reduced the likelihood of interference between the copper strands, which led to a better signal.
In the world of digital cables, there's no need for shielding since there is no possibility of interference within a cable. As for the thickness of copper, however, thicker copper will be able to extend the length of a digital signal, but for shorter cable lengths (two meters and under), there is no need for overly thick copper strands. In fact, thicker cables can sometimes be problematic since they are less flexible to bend around sharp corners and the increased weight can cause them to fall out of vertically mounted connectors.
Perhaps the most confusing aspect of an HDMI cable is cable length - how long can an HDMI cable go? You need to be careful when looking at cables that run 5 meters or longer. At these lengths, the manufacturing quality of cables has everything to do with whether or not they will work at longer lengths. For very long cabling needs, there are cable extender products that effectively boost the signal and extend the effective cable length. In addition, some HDTVs are designed with HDMI electronics that have greater sensitivity and active equalizer technology to accommodate longer cable lengths. In all cases, make sure you look at products that have the HDMI logo on them. This ensures that the product has been tested at one of the HDMI Authorized Testing Centers and meets the HDMI specification.
Digital cables are either compliant or they are not; they either work or they don't. Compliance is given to a specific speed rating, and the default speed that all HDMI logo'ed cables meet is 75MHz, which corresponds to 720p or 1080i video resolutions.
Unlike analog, there is no such thing as an HDMI cable that makes the digital audio or video data come out better than another. If the 1s and 0s make it to the other end, the cable has done its job, period.
CD: Some consumers have had problems with HDMI connections. What is the cause of this?
SV: Like any standard (I think of USB in particular), interoperability and compatibility can be issues, especially in early implementations. There are some products out in the market today that do pose compatibility problems. Most of these problems come about by improper implementations of the technology. Whenever problems like these are exposed, the HDMI standards group contacts the manufacturer and requires that the issue be resolved. In some cases, products have been recalled.
One of the classes of products that has been especially problematic is the set-top box. Some early set-top boxes were improperly designed. Some of these design issues were fixed, but unfortunately, many local cable service providers have still not upgraded their customers' set-top boxes with the new firmware upgrades or new boxes to make them compliant and compatible. The result: many customers may have set-top boxes with HDMI outputs that could be faulty and not work with certain TVs or with A/V receivers. Unfortunately, the only recourse any of us has is to complain to our local cable companies.
There is a new testing program, called SimplayHD that does test HDMI-enabled products for interoperability issues. SimplayHD testing is designed to promote greater interoperability between HDMI-HDCP enabled products from different manufacturers, as well as to help maximize that the ability of such products to receive and play premium digital content. You can find out more about SimplayHD testing at www.simplayhd.com.
In addition, you can always find out more information about HDMI by visiting www.hdmi.org.
Steve Venuti is the Director of Marketing for the HDMI Licensing LLC, the licensing agent responsible for administering the licensing of the HDMI Specification, promoting the HDMI standard and providing education on the benefits of HDMI to retailers and consumers. Steve actively works to build awareness for HDMI among consumers, retailers, installers as well as the 400 manufacturers who have adopted the HDMI specification.
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