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Unfortunately, things aren't that simple. There's another bag of influences affecting our cable. These can be divided into mechanical and external electrical influences and in some cases seem nearly senior in severity than the internal cable parameters.

With mechanical aspects, there's the dielectric of course. Audio signals are not neat constant currents but more like shock waves to which the physical construction of the cable reacts. These mechanical pulses interact with the various physical layers of a cable and their effects can be measured.

In fact, the security industry exploits certain of these effects such as with current detection when an intruder steps on a concealed conductor to create a small current when the insulation interacts with the signal-carrying conductor from his impact. Ditto for audio. Even a small bend in an interconnect can change the geometry and relationships of the internal layers when the geometry is instable. Now add external air pressure changes created by your loudspeaker. Audible effects can include distortion during high-level passages. Is the amplifier going berserk or are the cables misbehaving? Some cable manufacturers attempt to address these types of effects by fabricating extremely rigid cables, naturally at the expense of user-friendliness.

Other external influences are electromagnetic in nature and partially due to our modern lifestyles. Think electro smog. The room wherein our costly audio equipment sits is constantly bombarded by EM waves, never mind that each electrical device creates its own EM field the moment it's turned on. Components in close proximity such as is common in an audio rack will naturally affect each other. The maze of cables connecting to the components and the power grid (some of the shielded variety, some of the unshielded) do the rest.

There's power transformer radiation. There are GSM or UMTS cellphones. Loudspeaker may announce an incoming call well before the ring tone. Speaking into a cellphone activates its transmitter, which is reinforced by all the background noise and din of other people speaking. There are wireless handsets of landlines, clicking away when in standby and buzzing when in use. Don't forget halogen lights, energy-efficient bulbs, quartz alarm clocks, televisions on standby and the omnipresent PC. EM sources have become legion and our interconnects must shield the fragile audio signal from them. This means an electromagnetic shield as effective as possible.

Because we're clever and gifted cable designers, we incorporate all of these requirements to create a cable that's electrically optimal, physically still manageable and successful at warding off external EM interferences. Let's say the same for other equally clever and gifted cable designers and their offspring. Then why do all interconnects still sound so different?

The largest influencing factor on cable sound derives from capacitance or more correctly, reactance. Material choices and geometry determine whether cable reactance becomes a high-pass filter or HF attenuator. Different cables introduce emphasis in different bands to alter timbres.

But we are not done yet. The signal transmitted from component to component via cables is a complex event that's spread between 16Hz to 55kHz depending on software. Different frequencies propagate at different velocities inside conductors since we're dealing with an electromagnetic signal. In air, sound waves travel at a constant regardless of frequency (this constant is affected by humidity, temperature and air pressure as a function of altitude and weather). Light too is an EM wave that travels through air and vacuum – as are radio waves. The different propagation speeds of different light are nicely displayed with a prism, showing that red light for example travels slower than blue light.

Audio signal propagation velocities are thus dependant on frequency. Naturally, different arrival times at the ear are counterproductive. Phase differences, transient delays and harmonic shifts undermine signal fidelity. And while there is an address to force coincident time arrival for all frequencies in a cable, it's not a given that all cable manufacturers incorporate it. Their products can then sound dull or slow, soft or harsh.

This particular solution was devised by one Oliver Heaviside who was concerned over addressing this very issue for telephone lines. He invented a way to balance a cable's capacitance with its inductance. Velocity increase from capacitance was matched to velocity loss from induction. Skin effect presents high frequencies with higher impedances, incurs propagation delay and causes premature roll-off. To counter this effect, conductor coatings with a very thin layer of more conductive material than the core conductor (like silver over copper) is one solution. Another one is the use of multiple ultra-thin individually insulated conductors in Litz bundles.

Cable manufacturers next worried over conductor purity. The fewer impurities a copper wire contains, the less obstructions are encountered by the passing signal. As a result, we know expressions like 5-nines and 6-nines to represent 0.999999% conductor purity. Additionally, pure copper can be drawn in such a way as to build up molecules many hundred meters in length. Here reduced molecule-to-molecule transitions are the aim.

Cables and thus interconnects used to be made from copper before all manner of exotic metallurgic procedures were developed to create alloys of more noble character. The oldest form of copper wire is called Tough Pitch Copper. Its core material has been through the biggest ordeal of them all. It has been molten, cast into billets and then forced multiple times through an extrusion machine to become a length of wire in the desired gauge. The TPC wire is quite contaminated especially with oxygen that in time will oxidize to rust the conductor. This and the mechanical stresses caused by the extruding process have a negative impact on the sonic qualities of cables made from this type of conductor.