A conductor [wire/wires in a headphone cable] conducts or 'carries' the electromagnetic [electric] current / EMC from a source [a CD player etc...] that generates the current. This EMC is not uniform, the variations within, or the distortions of it, represent transcribed sound waves. The logic dictates that a wire that carries and facilitates the propagation of an EMC should have good physical properties to do so. An analogy of a dirty water-pipe semi filled with sediment and grease compared to a clean pipe and their respective and incomparable abilities to carry a 'current' of water can, to a degree, make the need for a quality conductor understandable.
With the passage of years the mark of 'quality' itself was being upgraded.
First it was the purity of the metal from which the wire was made,
then it was the purity of the metal and the metal casting method,
then it was the super-purity with 6, 7 and even more..Ns [Nines] - 99.9999..% content of a metal,
then the 'freezing' appeared
and OCC / Ohno Continuous Casting method of wire drawing/making,
now there is even CFDCT-UP-OCC metal available for cabling. [..can somebody decipher the mysterious designation ?]
...did I left out anything ?
Shielding and super shielding, on top of an already existing coat, also appeared on the scene. Later even a dielectric 'underwear' appeared under the coat.
The reasoning behind making of expensive cables for headphones has been that the EMC carrying modulations representing sound waves should have the best constructed optimal and unobstructed path, should have the minimal chance to be interfered with from within a wire and from outside of it. That's why 'purity', special casting, freezing, coats and shields.
There are headphone cables costing many hundreds of dollars, the price of some is over a thousand and even more. Well, they say the quality costs money.
Here is the question :
If copper and silver are the best metals to conduct the EMC, if they have the best properties to not interfere with the modulation of the current which represents and is, when converted, the sound, if it is even more best that the wires are made from pure as possible silver and copper, and even more, that the wires are 'cryo'[genically] transformed for a better electron flow, if all that is so important and crucial in making a top headphone cable then how come that all that carefully protected EMC coming from the source and travelling through a costly and specially constructed cable comes to and has to flow through a brass [ ! ] pin of a connector ? Never mind that this brass pin through which the current has to pass is coated in rhodium or gold, the integrity of the carefully preserved, up to that point, signal is compromised. Rhodium and gold are inferior to copper and silver in properties related to EMC conductivity, they have higher resistance to it and distort the sound more. Not all, or not 100% of a current flows through the plated surface of a connector pin. A large percentage of it goes through the brass of the pin. The brass with much higher resistivity creates 'eddies' or distortions in the current passing through it, it has more negative effect on the integrity of the signal. If you have a water pipe going to a house and it is cleany-clean except a bit of it that runs to the kitchen is clogged with dirt and grease, would you say that the water is clean and drinkable because 99% of the pipe is specially constructed and very clean and even has been 'cryo' freezed before being installed ? Why make an expensive cable, why care about the purity of copper and about the 'cryo' treatment and then terminate the cable with a brass plug ? It defeats the purpose of the effort. What about using the ox-cart wheels on a Mercedes Benz ? The similarity of absurdity is the same. Can I say it is almost a joke ? If the sonics of headphones, after costly recablings, are to the acclamation of many, much improved [how come, with brass connectors that are in the signal path ?] then how good they would be if the connectors were of the proper quality ? The businesses that make these expensive cables do not know this ? [Or they know but they still make money.]
Furutech makes silver pin/gold plated 6.5mm RCA connector, about the best there is but if the required termination is 3.5mm 'mini' then you are out of luck. Everything seems to be brass pin with gold or rhodium or silver plating. And the 'silver' is an alloy of silver and nickel. There is similar problem with the 4 pin balanced 'mini' XLR connectors. Amazingly no manufacturer is plugging this hole in the market.
Even bigger flies in the ointment are headphone cables terminated with 4 pin XLR connectors and then with adapters for different terminations. If the final termination is 3.5mm 'mini' plug then good luck with the compounded problem of two connectors with brass pins in the signal path.
The best connector would be the one made from an alloy of silver and gold [or to a lesser extent from an alloy of copper and rhodium], of about 97 % down to 95 % of silver and 3 % to 5 % of gold. Gold serves as an anti oxidant. The connector would have to be removable and replaceable after about 3 to 5 [give a better estimate] years as the audio signature of even silver 'fortified' with gold would deteriorate over time. That type of connector would be a proper fit for expensive cables, a proper connector to interfere least with a signal. Why no manufacturer or any enterprise in the business of producing and/or selling high fidelity audio equipment has given a proper attention to this ignored weak link in the audio chain is puzzling.
Does the brass connector problem demonstrate that much of the 'cables' science is no science but alchemy ? How much ? A bit, under a half, over a half, most of it, all of it [for the extremists] ?
What are the other contradictions in the science of cables, headphone cables in this case ?