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February 10, 2012
by Tim Kridel
By the end of this year, there will be more than 3.1 billion HDMI products installed worldwide, predicts the research firm In-Stat. That will be 34 percent more than in 2011, and it's just one example of how the video ecosystem is rapidly migrating toward HD.
That trend’s full impact isn’t always obvious. Case in point: Although all types of video signals are susceptible to electromagnetic and radio frequency interference (EMI and RFI) when transported over copper, HD video can be particularly finicky about its environment. That's partly because HDMI was designed for the consumer world, where the distance between a source and a display typically is less than 6 feet, so there's less cable to act as an antenna. But in offices and other commercial environments, cable runs in the dozens or hundreds of feet are the norm.
“HDMI’s Display Data Connection (DDC) is based on inter-integrated circuit (I2C)," says Christopher Bundy, Atlona product marketing director. "It’s very, very susceptible to EMI, so if you cross over some fluorescent lights or go by some 110 power, you’re going to pick up some interference.”
One solution is to transport the HDMI signals over fiber, but that's not cost-effective if it means replacing perfectly good Category cable that's already widely deployed throughout a facility. Instead, that money might be better spent on equipment designed to be reliable in interference-prone environments. “We spend an enormous amount of engineering time and testing to make sure that we’re designing around those issues,” says Joe da Silva, Extron Electronics director of product marketing.
Another potential solution is to use HDBaseT, which combines uncompressed HD video, audio, 100BaseT Ethernet, power and control signals for transport over a Cat5 or Cat6 cable.
“HDBaseT uses Pulse A Modulation 16 (PAM16), which uses the least susceptible part of the wave to transmit the slower information that comes over I2C," Bundy says. "It makes it so much less affected by EMI. That’s saving people’s butts left and right because not only are they able to utilize the full 10.2 Gbps of Cat5, they’re also able to get their control signals, which is what 90 percent of digital signals that get messed up.”
Although the selection of HDBaseT products currently is limited, some vendors expect the selection to grow simply because the technology has so many benefits for the people designing and installing HD systems.
“You’re going to start to see, for example, commercial data projector companies, releasing new products with HDBaseT inputs,” says Justin Kennington, Crestron’s DigitalMedia product line manager. “Now you’ve solved all of the problems with an HDMI connector: You don’t have a difficult-to-terminate cable. You’re no longer limited by HDMI’s range. You’ve got a locking connector that’s easier to terminate.”
But HDBaseT comes with its own set of considerations and caveats. “You have to have an HDBaseT transmitter and receiver at both ends, and you can’t run it into a standard router,” says Joe Andrulis, AMX vice president of marketing.
HDBaseT also has to managed carefully.
“Since HDBaseT is IP-based and carries a lot of information, it can easily overrun network traffic if not properly managed,” says Jack Gershfeld, Altinex founder and CEO. “It’s important to isolate the data stream from the video stream. In many cases, it’s as easy as running a local network for AV signals with a bridge to a data network for control and management. Look for products that have separate ports for signal transport and data/control transport.”
Distance and Signal Quality
Even if EMI and RFI aren’t an issue, it’s still important to keep an eye on cable length, particularly during the design stage. For example, when adding HD digital signage around a building, don’t assume that every link between each display and source will be a straight shot. If it turns out that the cable has to run in some convoluted path because, say, there’s an impassible wall or two in the way, the extra length could be just enough to cause problems.
“With video bandwidth of digital HD signals exceeding 3Gbit/sec per color, the attenuation of the signal becomes drastic as cable length increases,” says Gershfeld, whose handheld DIGI Sniffer product helps ferret out problems related to signal strength. “The DIGI Sniffer continuously measures the integrity of the HDMI signal and determines if the typical HDMI-compliant display device will properly recognize and display the signal. If your HD display is intermittent or has flickering lines or pixels, chances are you are on the edge of the cable capability.”
The HD video sources themselves also affect signal strength.
“For example, you might buy five different Blu-ray players, and if you put them on some kind of signal measurement device, chances are that you’re going to get three or four of those with different levels of signal output,” says Extron’s da Silva. “You don’t truly know what the baseline quality of that signal is.”
Scaling Up (and Down)
With analog, if you can get video to a display or projector, it's mission accomplished. With digital, delivery is just one step. For example, when a facility’s projectors and displays have a mix of capabilities, scalers ensure that each one automatically gets the right resolution.
“Imagine if you have several 1080p projectors and a couple of monitors that can handle only 720p,” says Creston’s Kennington. “Without a scaler, the only way to solve that is to tell your source to output 720p. Now you’ve degraded your high-end projector image for the sake of the smaller displays.”
Another digital challenge is content protection, particularly if the system has dozens or hundreds of displays. For example, if the system needs to distribute HD cable or satellite video, one solution is to use Pro:Idiom technology, licensed by Zenith, which is built into some displays or can be added via set-back boxes.
“Pro:Idiom encryption/decryption is what’s used to get HBO, ESPN and dozens of other HD channels to every room in a hotel,” says Andy Beaudet, a regional sales manager at Barco. “It’s now being deployed in other large venues such as stadiums and arenas. Pro:Idiom distribution uses either traditional RF coax infrastructure or IP streaming (UDP). Both Pro:Idiom and non-Pro:Idiom channels/streams can be intermixed without any difficulty.
“The advantage of this system is that broadcast HD Video can be distributed to a nearly unlimited number of displays. The disadvantage is that a Pro:Idiom distribution system does not scale down cost effectively below 50 or so displays.”
Tim Kridel is a frequent contributor to Pro AV and AV Technology
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