Anatomy of a Cable
A cable's basic job is to convey a signal from a source to another component in as near its original form as possible. To understand how a better cable differs from a cheap one, it's useful to know how a cable works. Since probably 95% of all interconnects are coaxial, we'll focus on how a coax cable is constructed. (Also see Inner Workings: Inside a High-End Audio Cable.)
The conductor normally is copper, though some high-end cables add a silver coating, which slightly increases conductivity at the extremely high frequencies required for video and digital audio. That's because signals at those frequencies tend to travel along the outside of the conductor rather than throughout it, a phenomenon called "the skin effect." The copper may also be specified as "oxygen-free," meaning that it contains very few copper oxide impurities.
The dielectric material electrically insulates the conductor and separates it physically from the wire-mesh shield, which acts as a barrier against EMI and RFI. In unbalanced cables, the type normally used in home systems, the shield also acts as a second conductor (essentially a ground - balanced cables have a third, separate conductor for this purpose). Because the mesh contains small gaps, most high-quality cables have a second, overlapping mesh shield, sometimes augmented with a foil wrap for additional RF protection.
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