Theoretically there should be no difference between well made cables with either metal.
That's one theory, anyway. Silver is a slightly better conductor in the prevailing theoretical sense. It is postulated that this is due to the greater number of particles in the silver nucleus than the copper nucleus, particles which are balanced with a greater number of electrons in the shells beneath the valence shell that contains the free electron. This better shields the free electron from nuclear attraction, so it is easier to move away from the nucleus.
That all looks really good until reality sets in and your silver wire tarnishes faster than your copper, or the solder joints on one cable are better than the other, or one set of wires gets work hardened and gets microfractures, overriding the small differences in conductivity of the wire. IME construction quality has a very large influence on how a cable sounds.
IME silver tends to sound a little more bright on average, a bit of emphasis that is often associated with the audiophile term "detailed" - which of course sounds like they rubbed the paint with clay and shampooed the carpets.
In practice, some cables may sound difference. remember, a cable cannot make the sound better. A cable can only degrade the sound.
A cable can only degrade the sound compared to the sound heard through a different cable. And that will be entirely subjective, since degradation is not a quantitative measurement in itself. However it's probably safe to assume that not using a cable degrades the sound more than using a cable.
