Simple question, or is it...

OK, let’s take a simple example of a fuse in an AC circuit. Describe in as much detail as you can what is traveling through the fuse wire and what is traveling outside the wire.

An audio signal is a representation of sound using electrical voltage in analog and binary in digital. That's  the first part. 
https://en.m.wikipedia.org/wiki/Audio_signal

The medium it travels in geoffkait explained above.

, if I’m not mistaken and I don’t think I am, that means the EM wave travels INSIDE the conductor. The E and M fields lie outside the conductor. They are stationary all along the length of the cable or wire. That explains why the type of metal, the purity of the metal and the physical non-symmetries of the metal influence the sound.