More misinformation exists about cable than most subjects in audio. Here are some simple facts that I hope all will understand -

• Audio cable is totally passive. It can add nothing to the signal. Just as no sheet of glass can make light any brighter, no claim by any manufacturer, that their wire can add anything to the quality of a signal can be regarded as honest, because doing such a thing is a physical impossibility.

• All cable alters a signal slightly. With good cable (i.e. wide enough coating, wire thick enough, shield far enough away from the conductors, and so on) there should be no significant effect on a microphone signal (usually between 1 and 50mV) below 100kHz over a distance of 100m.
   

• High quality professional audio equipment usually tries to be linear to 100kHz (with varying degrees of success!) It is technically not possible to go beyond that figure, because you are entering radio frequencies and then you would begin to pick up the BBC or Deutsche Welle and all kinds of other nasty things can happen. To stop this happening, all internal lines and ins and outs are 'tapped' to filter off radio frequencies.
   

• A cable manufacturer has to be able to smelt various metals into their various alloys and then draw them out into wire, cool them, coat them, wind and plat them and sheath them in PVC or other materials. It is a big operation.

• There are just a handful of cable manufacturers on Planet Earth. In Europe there are just two, Pirelli in Berlin (former Siemens plant) and Alcatel in France. All copper cable made in Europe has to come from these two plants.
  

• The audio cable names you see in the shops and in catalogues come from so-called cable confectioners, who buy cable from one of the few big wire makers and have their choice of coloured PVC on the outside and their names placed on the cable. They then put XLRs or whatever is required, on the ends and put the cables into pretty boxes. So the quality of the cable will depend on how far 'up-the-shelf' the manufacturer reached, when he bought them.

• Copper has become very expensive, so some manufacturers are using other metals, typically steel, for things like the shielding and some even use conductive-carbon shielding with an embedded steel wire. This may save money, but leads to other problems (poor shielding, greater induction between shield and conductor). 
   

• Some foil-screened cables work very well, but only as installation cables. They do not take kindly to being handled and bent around, as this can break the foil.

• Good quality mic pres with a relatively high input impedance and a robust (i.e. higher voltage) signal from the microphone are less effected by poor cable, than weak signals and low-impedance mic pres. Ribbon mics prefer low impedance mic-pres because they put out so very low voltages and therefore, the cable quality plays a bigger role.
   

• However - the higher the impedance, the shorter the cable run can be. So a high impedance sources feeding high impedance input (e.g. a synth feeding a line input on a desk) should not be longer than about 5m. For a large studio, this is a problem, because cable runs are nearly always longer than 5m, so synths plugged into the line-in can sound muffled (highs filtered off). To get around this effect, you can plug into the mic input and turn the gain right down, or better still, pad the signal at the instrument.

• The biggest improvement most studios can make to their wiring is proper grounding, so make sure that all earth wires are connected and all earthing (grounding) is unified (i.e. brought together in one connection) and also actually connected to Mother Earth via the foundations of the building.