Why construction of a HDMI cable is important
This post is sponsored by Metra Home Theater Group.
Metra Home has been a DPL member since its inception. Our association with DPL allows Metra Home Theater to “tap” into the solid educational service that DPL provides. These sessions expose many claims about HDMI and the confusion that comes along with it. To clarify this, we deconstructed an HDMI Cable into six important features in an effort to explain why one HDMI cable is better than another to our customers.
Cable Architecture and Timing, Intra-pair & Inter-pair Skew
Wire gauge and consistency of the twist ratio determine both inter-pair and intra-pair skew. It is not uncommon to see the twist point offset from the crossover center line in a lower grade cable. This failure to hold this specification can cause jitter in the audio and video data stream. Inter-pair skew is caused by the length and twist points variance between the TMDS shielded pairs and will manifest itself by showing sparkles in solid color or white on the display depending on which cable or how many pairs have an issue. It is important to purchase a quality HDMI cable to ensure good wiring architecture to avoid timing failures. HDMI is all about timing. Timing can be affected by poor wiring architecture within and between the twisted wire pairs, also depending on where and how the twist ratios are incorrect will determine whether the issue is intra or inter pair skew related. The graphic below illustrates the cause of each of these failures.
The two types of shielding that a good HDIMI must employ will provide the best protection by way of a braided and foiled shield. Braided shield keeps outside noise from interfering with your HDMI cable by cutting down the 110/60Hz interference found from power lines. If outside noise penetrates the HDMI cable it can cause intermittent operation or, in many cases, a total failure for the system to perform. Foil shields reduce the high frequency interference and keeps the noise within the cable. A foil shield also protects the internal high frequency transmission from getting out into other electronics within the same system. This can cause other anomilies to take place within the system environment. Better materials and more coverage within the shielding protects all of the system components and promotes a higher level of performance.
Thru-Put Bandwidth and Speed
How fast an HDMI cable sends data is one of the most important factors in cable performance. There is not one physical part of a cable that increases bandwidth and speed. Higher quality products will always yield better data transfer. A cable must be well built to be able to produce wider bandwidths and increased speeds. DPL certification on HDMI cables is a good way to know if the cable will provide the best bandwidth and speed.
Surface silver content and the type of dielectric play a part in the performance of a HDMI cable. Silver offers a lower insertion loss caused from skin effect. At higher frequencies signal data tends to travel on the outer circumference of each conductor. By using silver allows for better conductivity for any high speed signal data that rides on the outer circumference of the conductor. Proper balance between copper and silver is mandatory for consistent performance. Copper provides a stable high tinsel substrate for the silver plating, this will help the wire to keep its original length and shape which is necessary for the higher bandwidth and speeds.
Controlling the heat, silver content, quantity and flow of the solder will have a direct effect on signal performance. Proper termination comes with experience when soldering in small typically found in most HDMI Connectors. This means that solder must be applied at a higher temperature for it to flow. Higher temps mean a greater chance of thermal damage to the wires insulation. The silver soldering process is an earned talent since silver reacts to a limited plastic state before hardening. The heat and speed of each build requires many hours of practice and a high regard for patients. Solder work must be done with the greatest of care and a small thermal operating window.
Testing is necessary to make sure the cable meets the HDMI standards. Cables labeled as HDMI certified will have gone through expanded cable speed tests at an HDMI-authorized testing center to certify that they are capable of delivering bandwidth up to 18Gbps. The certification label will have a QR code printed on it that you can scan with your smartphone to verify the cable’s certification status and that it’s not a counterfeit product.