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 Why 2 Short HDMI Cables Yield Different Results

When it comes to HDMI performance, reliability has been the major issue, and it usually surfaces with people breaking the rules.

This is not new, we’ve been following specification rules since the invention of the wheel, so why has it now taken such a toll?

In our experience, some manufacturers have shown a lack of competency in making HDMI products right the first time and continuing that over the products’ life span. It is absolutely false that all cables are the same, even at short lengths.

DPL Labs is more than just a certification company. It offers additional services that manufacturers, vendors, retail operations and even distribution firms look deep into when they are either buying or building products to verify that the integrity is what they were promised.

These are called PDRs (Provisional Design Reviews). This service provides testing and examination of cables, Blu-ray players, switchers, A/V receivers and baluns from many firms.

Here’s an example: Two relatively inexpensive 1-meter cables came in for testing. They were being used with cable TV, so not such a big deal. When tested with one TV, however, only one of the cables worked, but with another TV they both worked. They were from two different manufacturers, and we were supplied two of each cable.

Upon testing and inspection we found that the integrity of the serial interface used to communicate the HDCP and EDID on one cable proved to be substantially slower in response compared to another cable that did work. By using different loads we were able to see, by way of an oscilloscope, that the rise times of these serial channels were very different. In an effort to expose why, we dissected each product.

Neither cable supported a shielded wrap around the video channels … that’s a first no-no. They both don’t twist the serial wires … sort of a no-no. However, the one that failed used a very thin solid gauge wire size for the HDCP/EDID channel compared with the cable that worked. The HDCP/EDID wires within the cable that failed are at least two times smaller in diameter than the one that worked. That smaller diameter HDMI cable was easy to bend and connect, but the consequences were dire, because the installer had no other cables to replace these, and it took yet another trip to the site to clear it all up.

Could the cable company still have made a thinner diameter cable with enough integrity for it to work with more devices? Yes! All it had to do was determine the intended cable length and predict, to some standard, the gauge of wires needed to support the video, supply voltage and the HDCP/EDID lines. Of course, the cable would not be the best cable in the world, but it sure would have had a better chance by decreasing the gauge of the video wires and increasing the gauge to the HDCP/EDID wires. When you make a product that sells for cheap, it becomes a give-and-take

with thanks to Jeff Boccaccio

So you thought you knew about cables?

This is simple compared to audio and networking!