Expert Interview: A Deeper Look at HDMI
HDMI has emerged as an important A/V standard, particularly in next-generation displays and components. ElectronicHouse.com spoke with HDMI expert Steve Venuti a few months ago to get an overview of the technology, and now Steve has returned for a battery of follow-up questions.
EH: HDMI is designed so that devices will automatically send the highest quality audio and video formats that are mutually supported, so this backward compatibility is done with a seamless intelligence that makes it easy for the consumer. But what if I have an HDTV with HDMI version 1, and the new DVD player or set-top box I just purchased supports version 1.3? Will I still get the benefits offered in version 1.3?
Steve Venuti: At the end of the day, HDMI -- in all of its iterations -- is a technology framework, where manufacturers have considerable leeway in how they build and deploy feature sets. The HDMI specification enables many great features, but it doesn't require manufacturers to build all of these features into their products.
HDMI's Consumer Electronic Control (CEC) channel is a good example. CEC is a set of features that facilitate intelligent, two-way interactions within a system, such as "one-touch" remote control of multiple devices. CEC functionality is completely optional; that is, a manufacturer can choose to build the feature into their product or they can choose not to. Although this feature is enabled by HDMI, it is not required.
There is a big difference between enabling something and requiring it. If a manufacturer decides to incorporate CEC functionality, we make sure it is implemented completely and correctly through our compliance testing process.
To put it another way: The HDMI version number does not translate to a particular feature set, and it is not really meaningful to the end user. It is much more productive and relevant to shop for the features you want, not the HDMI version. And likewise, the test for whether a new device will integrate fully with older equipment is in the feature set that it supports, not the HDMI version.
EH: If I have an HDTV that doesn't have DVI or HDMI inputs, but I purchase a DVD player with HDMI, is there a way to benefit from the HDMI on the DVD player?
SV: No. There is no way to legally convert a digital signal from a high-definition, digital-output DVD player to an analog signal into a TV.
EH: If the display has HDMI and I only have analog components, is there a way to still benefit from HDMI?
SV: It is physically possible to connect analog components to an HDMI-enabled display, but there will be no benefit to doing so. The signal is still converted from analog to digital (loss of quality) and there will not be any of the two-way communication that HDMI offers.
EH: Can analog and HDMI displays and components be hooked up together?
SV: Once again, it is not possible to go from HDMI to analog, but it is possible to go from analog to HDMI. While not as pristine as a digital connection, it will get the job done and can manage the number of cables behind your TV. Today, nearly all HDMI-enabled home entertainment products have analog interfaces, in order to ensure that all components can work together. In such cases, you will not get the benefits of HDMI, but your system will work.
EH: Do you have tips for troubleshooting an HDMI issue?
SV: First, let's keep things in perspective: the vast majority of HDMI installations are successful, and problems are very rare. On the other hand, you have increasingly complex components and systems, and as with any new standard there are going to be a few issues, especially with early implementations. If users encounter a problem, they should always make sure that HDMI connectors are securely seated in their sockets. Occasionally we see problems related to protruding screws near the socket or too much over-molding on the cable connector -- this results in cables not seating effectively.
In addition to form-factor issues, there are a few others to watch for:
First, there are some non-compliant HDMI switch boxes out there that degrade a signal and/or can't handle High-Bandwidth Digital Content Protection (HDCP) functions reliably. These are easy to spot because they don't have AC power. Passive switches may work for some very short cable runs, but we think that powered switches are the only way to go.
Second, we have seen some problems with implementation of HDCP in early versions of certain devices. HDCP requires that a security "handshake" be continuously maintained between devices; this is also known as the "authenticate forever" function. Occasionally, a DVD player or digital set-top-box will improperly implement this function, resulting in source-switching errors. In other words, when the user switches back and forth between TV inputs, he or she may experience a blue screen. The short-term answer is to power the system off and back on again; the long-term solution is probably a firmware upgrade from the manufacturer.
Another problem we've seen with HDCP implementation is the repeater error, where a source device has no trouble communicating directly with an HDTV, but it cannot pass the same signal through an A/V receiver. Again, the problem is most likely with the source device, and it can probably be fixed with a firmware update.
It is important to know that in all of these cases, these devices are not compliant with the HDMI specification. HDMI Licensing LLC is working with manufacturers to rectify such problems. HDMI implementations will continue to get better as manufacturers gain experience with some of these common issues. Also, Intel's Digital Content Protection subsidiary has recently released a test specification for HDCP to help ensure that HDCP is always implemented correctly.
EH: Some displays now offer three HDMI inputs. I would imagine the more the better. However, what does the consumer do when there is only one HDMI input and they have more than one HDMI component?
SV: A/V receivers with multiple HDMI inputs can be found for as little as $400. Switch boxes with up to four HDMI inputs are also commonly available. But a simple switch box is not your only option; there are some higher-end switch boxes that also perform video processing functions -- in many cases, better than what your TV can do. In cases where you want to add high-end video processing and many not want to spend a lot of money on an A/V receiver, these products offer the perfect solution.
EH: Are all HDMI devices, cables and connectors created equal?
SV: The HDMI standard sets a baseline for minimum performance requirements, but beyond that, we let the manufacturers differentiate in the marketplace. We are enablers, and manufacturers get to choose what features to implement based on the price and functionality expected by their customers. Some manufacturers choose to take advantage of all the features you can implement over HDMI; others choose to implement fewer of the features. But in every case, the fundamental thing that HDMI does -- send uncompressed HD video and audio over a single cable -- is common to all implementations. If one device sends a 1080p signal to another device over HDMI, the other device will receive that signal, no matter what other features the manufacturers have implemented.
As for cables, most home users will see no issues at all in 2-3 meter cables, regardless of the manufacturer. But in some applications, particularly 1080p signals and longer cable runs, we have seen differences in performance. Consumers should be sure that the cables they are buying are rated for their specific performance requirements (e.g. 1080p). Also, we recommend that consumers consider buying repeaters or some other active signal enhancer for longer length cable runs (typically those over 8-10 meters)
EH: Has HDMI taken over Digital Visual Interface (DVI)?
SV: HDMI overtook DVI several years ago. HDMI is now the de facto standard for connecting A/V equipment, and DVI is rapidly waning. DVI is still seen as a backup connection in some devices, and in a few key markets -- primarily desktop PCs (though not media PCs or Blu-ray/HD-DVD capable machines) and video projectors (which may not have a need to receive audio). Nonetheless, HDMI is rapidly gaining on DVI in the PC space as well, including graphics-card solutions from NVIDIA and ATI with HDMI outputs.
EH: What is the correlation between HDMI and HDCP?
SV: HDCP is not required under the HDMI spec, and it is licensed to manufacturers by a subsidiary of Intel. However, HDCP and HDMI are widely deployed together. HDCP is a must-have for "premium" content like HD movies and pay-per-view events, and it doesn't work through anything but an HDMI or DVI connection. In other words, HDCP is facilitated rather than required by HDMI, but it's a practical necessity for anyone who wants access to the best HD content. HDCP works quietly in the background: users won't know it's there, and they should not worry about it.
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. More information HDMI is available through www.hdmi.org
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