High definition multimedia interface (HDMI) cables represent the HD audio standard. Increasingly replacing optical and coaxial connectors on many devices, HDMI offers increased audio options, and carries high definition video. However, compared to optical cable, HDMI's general superiority may or may not be relevant in your individual application. The question a user should be asking in choosing a cable is, "What is it best for?"
HDMI enables the use of lossless audio codecs present in Blu-ray disc players. Used in conjunction with a compatible receiver, Dolby TrueHD and DTS Master Audio formats represent the pinnacle of home theatre sound. These sound formats are duplicates of the audio master, devoid of compression that might degrade sound quality. Optical cables can pass standard digital audio formats, such as Dolby Digital and DTS, but cannot pass the dense lossless audio formats due to bandwidth limitations. If you are not using a Blu-ray player, optical and HDMI audio are identical. Optical cables are also used on Blu-ray players in systems that cannot decode HD audio formats. These are compressed at a lesser extent than Dolby Digital/DTS, but are not at the level of quality of lossless options. These are referred to as "core" formats.
Optical cables are internally "wired" with glass or plastic fibres. HDMI is comprised of a series of twisted copper or silver cables, reminiscent of Ethernet cables. As a result, in most cases, HDMI is a potentially superior cable in terms of durability. If kinked, optical cables can be accidentally broken internally, causing signal transmission failure.
Maximum Run Length
HDMI cables have an effective distance of 50-75 feet before they require a repeater to prevent intermittent operation. Optical cables, due to the high attenuation of the light transmitted on the internal fibres, are realistically limited to 20 feet. It is important to remember that HDMI is passing high definition video (and potentially HD audio) while displaying superior resistance to signal loss over distance.
Noise and Interference
Optical cables transmit their signals using light. This transmission does not require a conductor/ground relationship as mechanical cables do. Although HDMI is generally immune to noise stemming from two devices sharing two different grounds, they can still pick up electromagnetic and radio frequency interference. Known as a ground loop, this interference commonly shows itself as rolling bars on-screen, or a low-frequency hum in the audio system. Optical is completely immune from these issues. These interference types are potentially an important thing to consider when making long cable runs through walls and next to other cables.