HDMI: Here, there, everywhere!
There once was a time where high definition signals were somewhat stationary – they could only be transmitted within a few metres of the signal’s source.
Nowadays HD signals can be distributed around a home wirelessly, over a local area network (LAN) or even over the powerlines, all in line with the HDMI Adopter guidelines.
“HDMI distribution over such technologies can enhance convenience for the AV installer, from a structured wiring point of view,” explains Kordz managing director David Meyer. “However, it may come at a cost to system stability, reliability and performance.”
So it really is a case of ‘buyer beware’.
“The HDMI specification is governed by the Compliance Test Specification (CTS). Such alternate conveyance products would most commonly be classified as repeater devices, and the spec is clear in this regard: native HDMI single goes in, native HDMI signal comes out. But the CTS does not govern the quality of the content within the Transition Minimised Differential Signalling (TMDS), such as the on-screen performance of the video.”
WIRELESS FOR HDMI
If you do choose to install a non-cable HDMI solution, it would be well advised that you align yourself with a reputable company that has a long history with HDMI Licensing, LLC, such as Gefen, distributed in Australia by Amber Technology.
“Retrofits are where wireless solutions are particularly well suited,” explains Gefen president and chief executive Hagai Gefen.
“Any location where you cannot run cabling in the walls, like in historical buildings, will benefit because you can upgrade to HD video without breaking into the walls to run cables. Presentation environments that don’t want cables lying around will also benefit from a very clean wireless installation. Any challenging mounting installations can also benefit, such as when displays must be mounted on ceilings or other areas with no ready access to cabling.”
So, how exactly does Wireless for HDMI work?
“It’s actually very simple,” Hagai says. “The GefenTV Wireless for HDMI sender and receiver units come equipped with a 36 array internal antenna operating in the 60GHz radio range to send HDMI at 1080p Full HD up to 10m in distance with no cables required.
“It delivers uncompressed video and audio that remains in the HDMI format for a top-notch performance with no signal degradation. Advanced, high frequency radio technology supports a high gigabit transfer rate along with eight channels of digital audio. To operate perfectly a line-of-sight installation is recommended so that the sender and receiver units face each other with no major obstructions in between them to deter the radio signal.”
Much like an HDMI cable, there is no special knowledge needed to operate the GefenTV Wireless for HDMI solution. It’s a true plug and play product that works out of box provided the recommended procedures are followed, such as line-of-sight mounting between the sender and receiver units.
“As long as you stay within the maximum distance (10m) and you have installed the sender and receiver units in a line-of-sight configuration, you should not experience any signal degradation at all,” Hagai says.
“And because the GefenTV Wireless for HDMI extender uses the 60GHz band, it will not interfere with other devices operating in a typical home installation environment.”
HD OVER IP
Another solution that has proved to be quite popular is Just Add Power, distributed in Australia by Advance Audio. It allows installers to distribute an HD signal around an existing LAN, extending transmission well beyond the capabilities of certified HDMI cables.
“An installer should use our HD over IP devices for any application where they need to distribute HDMI content from one or more sources to one or more screens,” says Advance Audio operations and marketing manager Chris Strom.
“It is a consistent and reliable solution that is easily adapted to practically any environment. The primary benefits are unmatched flexibility and scalability, without being bothered with the things that affect legacy HDMI matrix and balun devices (e.g. distance concerns, HDCP errors and signal processing problems).
“Essentially we only make two things – encoders and decoders. The encoders (aka transmitters) convert the ones and zeros in a HDMI signal to ones and zeros that are compatible with an Ethernet LAN. The decoders (aka receivers) convert those Ethernet ones and zeros back to HDMI ones and zeros. The whole process is encrypted and very fast (typically it takes about 37 milliseconds for the encode/decode).”
But, how far can an HD signal be carried over IP?
“The answer to this question often amazes the installers who have had to suffer through the legacy HDMI balun products from other manufacturers,” Chris says.
“Our HD over IP signals can be carried across practically any size LAN as long as it has been built to sustain the network connection without interruptions. I am personally aware of an HD over IP installation in New York City that sends a signal over 10km between buildings via their company’s fibre backbone.
“Another extreme distance installation I am aware of is a television studio that is sending their HD over IP signals over 32km from point to point using their Ethernet Radio wireless network extenders. That Ethernet Radio technology works for distances up to 140km, at which point the curvature of the earth impacts the signal.
“With a properly configured network there is really no limit to the distance you can cover with the Just Add Power solution.”
First generation (1G) Just Add Power devices use a JPEG compression technique that has a very small impact on the video signal. This can be minimised by setting the HDMI source to the highest possible resolution settings. With the second generation (2G) devices, the company has implemented a lossless CODEC.
“The only thing we advise 2G installers to do is make sure that their sources are set to ‘progressive’ video output if at all possible. We have found that interlaced signals do not look as good as progressive signals and should be avoided if possible.”
Simple distributed AV installations don’t require advanced knowledge or programming skills, Chris says. But installers who want to take advantage of the more advanced features such as ‘On Screen Display’ messages, distributed RS232 control and video wall processing will need to have a good understanding of RS232 and/or IP control systems.
“While the control commands for the Just Add Power solution are really quite simple, the magic is in the integration and that’s where a talented systems programmer with more skills can deliver more function to the customer,” he says.
A CAUTIONARY TALE
For David and his team at Kordz, however, “cable is king”.
“There’s nothing wrong with using non-native HDMI extension or distribution technologies, as long you understand them and know what to expect. Many non-native solutions use some form of compression, and even though they may claim to be ‘visually lossless’, the truth is that loss is loss,” he says.
“Any solution that decodes HDMI, packs it into some other form of transmission and then reconstitutes the bitstream at the other end simply needs to declare itself as such in order to give the custom installer any chance of troubleshooting interoperability issues. Predictability comes from knowledge and understanding.
“At Kordz we prefer to stay away from anything that uses compression, as we believe it compromises the foundation of HDMI. Granted in some applications it may be justifiable (e.g. small TVs in remote rooms) – just as long as you know what you’re using.”
As far as non-native HDMI technologies go, Kordz has developed an HDBaseT-based extender that does not unpack or in any way compress or modify the HDMI signalling, retaining high speed data rates along a single, unprecedented length of Cat X cable.
It does this by keeping any HDMI silicon (i.e. transmitters and/or receivers) out of the circuit. To include them would limit data rates to 6.75Gbps, a five year legacy of HDMI v1.3. Upcoming new generation HDMI silicon could increase that to 9Gbps, but leaving it out entirely enables the full 10.2Gbps.
David says most installers are just concerned with whether something works, not if it’s compliant, and that can backfire.
“I believe that selecting the best product would be a lot easier if everyone was more transparent. For example, with a wireless product, don’t assume it’s native HDMI protocol burning through the air just because it has HDMI in at one end and out at the other. Quality uncompressed signals are good for about 10m, with longer range examples likely using some form of compression.
“Same goes for powerline, which in some examples may only work in the SD realm, and possibly even compressed at that. IP and technologies like HDBaseT are great as they may not compress a signal, but they may have other limitations. Whatever the solution, disclosure and understanding is the key to designing a reliable system.
“Recognising the difference is critical. I’ve even seen claims of an ‘HDBaseT matrix switch’, but it was just an HDMI matrix switch (6.75Gbps limited) with HDBaseT on the output stages – it’s a different beast to that implied. With any such products, just learn to ask questions in order to better understand what you’re dealing with.”
David says the inimitable Joe Kane, of Video Essentials fame, sums this up in his Proof of Performance seminars.
He says: “You should know exactly what you’re using and you’ll be able to better predict the success of an installation.”