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.
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 need to maintain signal integrity, ensuring compatibility between devices, and working with HDCP. However, there are special considerations for addressing these challenges when projects are larger scope and complexity. Here, we tackle three major challenges.
As with analog video, digital video signals such as HDMI are subject to losses as they travel along a cable. Analog losses tend to be gradual as cable length increases, and will degrade image quality gradually. Digital signal losses, on the other hand, include attenuation and jitter that can result in abrupt gaps of lost image data, and will likely be disruptive to image display, even disabling it completely.
Common symptoms include color sparkles, flashing and a blank screen. The best way to prevent digital signal losses is to take measures to maintain signal integrity from source to display. One of these is the proper selection and length of cable for HDMI signals.
In a commercial A/V environment, audio and video signals typically have to travel much longer distances than in a residence (where HDMI has gained more traction). 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 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 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.
Cables are not the only consideration for signal integrity. Some source devices may output sub-par HDMI signals with insufficient voltage to withstand appreciable cable runs. An HDMI signal path may include several devices between the source and display, such as switchers, splitters, or video processors.