Digital Coaxial (RCA)
The digital coaxial interconnect is capable of transmitting high quality digital audio such as Dolby Digital 5.1 and DTS surround sound. The fact that it carries these digital signals makes it a better alternative to its analog counterparts. The coaxial interconnect is commonly seen as a source output on DVD players, cable/satellite boxes, HTPCs, and other higher–end Home Theater Network gear.
Digital coaxial uses the same RCA interconnect as a composite video RCA interconnect. The cables are even interchangeable since they both have the same 75 Ohm impedance and similar bandwidths.
Audio through an optical (or TOSLINK) interconnect is digital and is generally higher in quality than its analog counterpart. Fiber optic interconnects use light to propagate digital signals as opposed to regular copper wires using electrical current. The digital light signals can carry S/PDIF, Dolby Digital, DTS or any other audio signal.
The fiber optic cables that attach to an optical interconnect can vary in diameter. Sizes include 1.0mm, 3.5mm, 5.0mm, 7.0mm and more. Larger diameter cables are usually more expensive, but they can carry more bandwidth and can propagate signals for longer distances. Mini-Toslink interconnects are also available, and are generally used for mini disks, and other small digital audio devices.
Optical has a few advantages over its copper counterpart. EMI noise will not affect optical signals since data is transferred in light. Also, optical interconnects do not carry any ground signals where noise from other electronic devices can propagate into the audio signal. One disadvantage of optical interconnects is the extra processing steps involved in converting current to light and then light to current. These two steps can add another source of error into the audio signal. Another disadvantage is that optical cables lose their signal strength in bent cables. Care should be taken to keep the cables as straight as possible.