May/100
Commercial HDMI Cable Installs Issue
HDMI is quickly making headway into commercial A/V with the proliferation of HDMI interfaces on displays and source devices including laptops, Blu-ray disc players, and digital satellite and DVRs.
End users of commercial A/V systems, well aware of HDMI in home A/V, are asking integrators to implement HDMI in commerical A/V installations. As a result, the industry is quickly transitioning toward digital video and adopting HDMI as well as DVI, DisplayPort, and SDI.
Integrators working with HDMI in commercial A/V face essentially the same challenges as residential custom installers – maintaining signal integrity, ensuring compatibility between devices, and working with HDCP.
However, there are special considerations for addressing these challenges in professional A/V integration, due to the much larger scope and complexity of commercial systems compared to a home system. Here, we tackle three major issues.
Signal Integrity
In a commercial A/V environment, audio and video signals typically have to travel much longer distances than in a residence. Cables usually have to be installed in tight, limited spaces, and integrators want to be able to terminate them easily. Transmission requirements can range from as little as 25 to 50 feet, to several hundred feet, and even up to several miles when sending A/V signals between corporate or university campuses. Standard HDMI cables may be sufficient in applications with relatively short distance requirements, but will not be adequate for longer distances, for which other mediums including twisted pair and fiber optic cable should be considered.
To help ensure signal integrity in short-range applications, select high quality 2 metres HDMI cables rated by the manufacturer for the distance required. When using long HDMI cables to cover distances significantly beyond 50 feet, a cable equalizer may be necessary, especially at high resolutions including 1920×1080.
A cable equalizer attaches to the end of a long cable run and restores HDMI signals by compensating for cable losses. To provide for advanced HDMI features and capabilities such as deep color and 3D, high-speed 2 metres Mackuna HDMI cable should be selected if there is a potential for future system expansion or upgrades.
For distance requirements exceeding around 100 feet, an alternative to standard HDMI cables is a transmitter and receiver set that sends signals over twisted pair cable. Twisted pair is a proven medium for extending digital video signals, and integrators often prefer twisted pair cable since it is inexpensive, easy to pull through conduit, and can easily be field-terminated to custom lengths. When very long transmission distances are necessary, fiber optic cable and fiber optic A/V devices are the solution. A/V signals can travel for miles over fiber with negligible loss.
Device Compatibility
HDMI and other digital video formats utilize EDID (Extended Display Identification Data) communication, originally developed for use with analog VGA ports. EDID communication is a two-way data exchange that allows a display to convey its operational characteristics, such as its native resolution and refresh rate, to the source device, which then generates the necessary video characteristics to match the needs of the display.
This automates and optimizes compatibility between the source and display, without requiring the user to configure them manually. In pro A/V applications where computers are the most common source devices, EDID communication can save significant time and effort in system setup.
EDID was intended for a single connection between one source and one display. The situation becomes considerably more complicated when a signal needs to be split or routed. Distributing a signal to multiple displays may not be a problem if they are identical, but what if they are different, at various native resolutions? An integrator may select one display to establish EDID communication with the source, and then roll the dice on the others.
With either approach, the switching or distribution device always maintains EDID communication with all connected sources, even with a signal switch or split. An HDMI matrix switcher may include more sophisticated EDID management, due to the fact that separate EDID communication is required for each input / output tie.
Content Protection
The first is that all devices in the system, from source to display, must be HDCP-compliant. That may seem obvious to a residential integrator, but commercial A/V integrators may not be fully aware that just a single, non-HDCP compliant device, such as a simple HDMI switcher, can disable Blu-ray disc playback for the entire system.
Second, commercial system designers need to be aware that HDCP rules allow for a maximum of 127 devices downstream from the source, with up to seven levels of repeaters allowed. A residential installation is not likely to approach these limits, but system designers may be concerned if they’re working on a large commercial project that calls for HDCP compliance throughout. Certain source devices including Blu-ray disc players have been known to allow for much less than 127 downstream products, often even less than 16.
Some residential and commercial A/V integrators have decided to work around the issues related to HDCP by deploying analog-based video signal routing. This is a temporary solution, since the ability to deliver to analog high definition video output may be impacted in the future by the AACS-mandated “analog sunset,” and possibly other content protection provisions that could limit or disable analog output on HDMI-equipped devices.