Induction

 A common means by which extraneous signals enter the audio path is through induction. All current produces a corresponding electromagnetic field that radiates from the conductor carrying the current. Conversely, a radiant electromagnetic field can induce current in a nearby conductor, introducing unwanted signals into an audio cable. Balanced lines are much less susceptible to induced noise because of the phase reversal in the wires. Two common sources of induced noise are RFI and EMI.