Q. There are so many HDMI cables out there, what are the differences between cables labeled 1.2, 1.3a and 1.3b and are there limits to the lengths of these cables in order for them to work reliably? - John, Upton, MA

A. HDMI cables come in two categories: Standard and High Speed. These are new categories so manufacturers are just starting to label their cables this way. Essentially, Standard cables have been tested to perform at speeds of 75Mhz, which is the equivalent of a 1080i signal.  High Speed cables have been tested to perform at speeds of 340Mhz, which is the highest bandwidth currently available over an HDMI cable and can successfully handle 1080p signals including those at increased color depths and/or increased refresh rates. High-Speed cables are also able to accommodate higher resolution displays, such as WQXGA cinema monitors (resolution of 2560 x 1600).

Typically, when manufacturers refer to a “1.3” cable, they mean it has been tested to the new high bandwidth capability of HDMI and can run 1080p and beyond. A cable tested at the 1.2 testing specification would have only been tested to perform at 1080i. The “a” and “b” are internal designations that have no bearing on the features, functionality or performance of a product.

As for length, cables that bear the HDMI logo are required to be tested at the actual length of the product that is being sold.

Steve Venuti - Vice President of Marketing, HDMI Licensing, LLC

Steve Venuti is the Vice President of Marketing for the HDMI Licensing, LLC, the organization responsible for the development of the HDMI standard. For more information about HDMI, check out the HDMI Knowledge Base.