Depends on the signal level and the impedance. For speaker cables, all you need is a big enough gauge to carry the current. But for low level signals, especiall

Depends on the signal level and the impedance. For speaker cables, all you need is a big enough gauge to carry the current. But for low level signals, especially less than line level (magnetic phono cartridges, microphones, guitar pickups) a good quality cable with proper impedance and low capacitance can make a big difference. If you look at professional studio and broadcast supply catalogs, you will see mic cables with a specified capacitance per foot -- that's a spec that engineers look for. And I can personally vouch that an expensive guitar cable sounds better than a cheap one -- I was a skeptic until I tried one, and compared it with the standard cable I had been using. The difference wasn't subtle.