Usually abbreviated “EMI,” electromagnetic interference is a disturbance in the radio frequency spectrum generated by an external source, which affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data.
Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: automobile ignition systems, mobile phones, thunderstorms, the sun, and the Northern Lights. EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions. Most audio devices and audio gear that isn’t properly shielded is susceptible to EMI, and if the interference is strong enough, even shielded gear is vulnerable.