High-end audio cable
High-end audio cables are claimed to improve the sound quality of high-fidelity audio systems. Since the audio signal passes through cables on its way from the source to the amplifier, or from the amplifier to the speakers, the cables will affect that signal. Basic system frequency response can be calculated from the electrical properties of the cables, and components on either side of the cables. These electrical properties include resistance, capacitance, inductance and electrical conductance. All cables will affect the audio signal in a number of other ways that are not predicted by the resistance, capacitance, inductance and electrical conductance. For example, science predicts that shielding, and the triboelectric effect will play roles in cables depending upon the application. The perceived quality of the sound reproduction is influenced by psychoacoustic effects.
Controversy
There is controversy among audiophiles surrounding the impact that cables have on audio systems. While it is a fact that cables change the audio signal, the audibility of the changes is questioned by many.
On one side of the controversy are some cable manufacturers who are willing to provide evidence of the impact that their cables make. A carefully-made frequency response plot is a direct measurement of the difference that cables can make in the playback of a system. Attenuation of the high frequencies (roll-off) of the audio signal can be explained by the effects of capacitance and inductance of the cables used in the system. In short, the energy stored in the capacitance and inductance of the cables will affect the flow of energy from audio signal source to load, causing attenuation which varies depending on the frequency of the audio signal.
On the other side of the controversy are claims [1] [2] that indicate that even among audiophiles, in a double blind test it is difficult or impossible to distinguish extremely expensive, exotic speaker cables from ordinary lamp cords or budget 12AWG copper speaker wire.
It should be noted as anecdotal evidence that the audio cable industry has grown substantially over the last 20 years as customers purchase more and more high-end audio cables with the goal of improving their audio systems. In addition, virtually all major high-fidelity audio publications regularly review audio cables for their sonic attributes.
Digital Cables
One of the more contentious areas is in digital cable design, with high end cables being sold with claims of "distortion-free signal transfer" [3]. Some have argued that since digital data transfers incorporate error correction then any cable that is capable of transferring bits should provide distortion free signals. The bit rates (approximately 1MBit/s) and distance travelled are considerably lower than for other data transfer technologies such as gigabit ethernet.
It has been suggested that because the timing signal is sent as an analogue signal that if the wave is distorted by an incorrectly specified cable the incoming bits may be assigned to the wrong time bin, thereby distorting the sound. However, provided it is industry standard 75 Ohm cable then there remains considerable controversy among audiophiles over whether a high end cable provides any improvement over an entry-level $3 cable. [4]
Cable theory
There are almost as many theories as to how an audio cable improves the sound as there are manufacturers.
Common theories of cable design
Some manufacturers of low- to medium-end cables as well as do-it-yourself cable designers stick to the basics of capacitance, resistance, and inductance. (Hereafter referred to as a group by LCR, where L is the symbol for inductance and C for capacitance and R for resistance.) They are also noted for their critical approach to selecting materials based on dielectric properties (for insulators) and resistive properties (for conductors) and all electrical properties for geometry.
The conductors are generally at least made from high-purity copper or even silver. (Some audiophiles see silver as having a "bright," "harsh" sound with "glare," though this may simply be the synesthetic effect due to the color of the metal. Many silver-based cables have been subjectively reviewed as sounding completely unlike this common characterization.) Often, manufacturers will use oxygen-free, "long-crystal," or high-purity copper, though the particular benefits of these traits in an electrical sense are unproven with regards to audio transmission. Practically, all copper intended for electrical purposes is oxygen-free and of high purity.
These cable designs are often easy to make at home, with popular "recipes" for budget high-end audio cables published by Jon Risch.
Higher-end cables are often characterized by expensive and exotic materials, as well as exotic geometries. They are usually manufactured for the vendor, whereas many lower-end cables are handmade from raw stock or incorporate ready-made cable types from vendors such as Belden or Canare.
Missing from most of these is the fact that the shield should be connected ONLY at the source end to prevent circulating currents in the shields! This fact is well established in circuits involving critical measurements.