I was watching a short tutorial video about balanced audio, and the guy claims for unbalanced transmission even there is shield in coax cable "hum and noise still gets true". But in wiki it says: "Coaxial cable also provides protection of the signal from external electromagnetic interference."
So I was wondering does a coax cable is worthless to shield electromagnetic interference? If so what is the benefit of using it rather than a zip cord.
Basically what I'm wondering is imagine a single ended(non-differential) signalling. What kind of noise coax shield would reject better comparing to a zip cord? Or should we say coax mitigates the noise but still passes some? I observe myself 50Hz noise when I use coax cables. So why are they used instead of zip cords besides the reason impedance matching in RF?