Failure Modes in HDMI Transmissions
In a digital video system such as HDMI, there are minimum performance requirements for both the High Frequency Video Data (HFVD) and Low Frequency Control Data (LFCD) as set by the HDMI adopters. As long as both the Video Data and Control Data transmission systems perform above the minimum standard, the interface functions normally.
Typical video data transmissions deficiencies can produce a snow like appearance or random sparkles over the entire screen, predominantly in dark areas. An increase of data loss can even result with total video failure. The specific artifact as seen on the screen varies from monitor to monitor and is dependent on the nature of the failure.
Control Data Transmission deficiencies usually manifest themselves as a loss of sound, erratic color schemes, intermittent operation, and loss of picture or a loss of both picture and sound. Again, the specific artifact can vary from manufacturer to manufacturer.
However, the cable is only one part of the data transmission system. The performance of the system is also dependant on parameters residing in the Video SOURCE (DVD player, Set-Top Box, etc.) and in the Video SINK (TV Monitor). These parameters can vary from manufacturer to manufacturer. As more products are added to the market, the risk that one or two of these devices is operating on the edge of the HDMI specification is increased. Remember, the integrity of the entire interface is accumulative in nature. Having a cable with headroom ABOVE the minimum specification can make up for some types of deficiencies associated with components of the system (SOURCE and SINK).
The eye patterns below illustrate the difference between a high integrity cable verses a low integrity cable. The black area between the mask and the eye pattern itself is the safe area with no noise, robust symmetry, and maximum distance between the pattern and the mask.
 Good Eye Pattern |
 Poor Eye Pattern |
| The eye pattern above is a near perfect eye. The dark blue area in the middle is called the eye mask. Its purpose is to define the specification limits for each kind of transmission one may be testing for. HDMI has its own sets of specifications for each resolution. This near perfect eye will earn points toward a higher DPL Rank. | The eye pattern above is close to breaching the mask called "Kissing in the dirt". The white area in this sample is the distance in margin between the mask and the eye itself. The closer you are to the mask the lower the mask margin and the higher the risk. Allow for just one abnormality to occur and system failure can occur. Just the pure nature of cable tolerance can put this system in jeopardy. With this poor response this device will loose points and will yield a lower DPL Rank. |
