AC stands for Alternating Current, a type of electrical current in which the flow of electrons changes direction periodically, going back and forth. In the world of audio, this is how sound signals are represented electrically.

Essentially, every audio signal is an Alternating Current (AC).. The logic is a direct analogy with sound waves in the air:

• Air compression (increase in pressure) is represented by the flow of current in one direction.

• Air rarefaction (decrease in pressure) is represented by the flow in the opposite direction. This oscillation of electric current is the electrical "image" of the oscillation of air pressure that forms sound. It is the opposite of Direct Current (DC), which flows in a single direction and is used to power the circuits of equipment (like the energy from a battery). Therefore, in audio equipment, DC powers the device, while AC is the sound signal that passes through it.