Noise on a circuit that can be caused by voltage spikes in equipment, voltage changes on adjacent pairs in a copper cable, tones generated for network signaling, maintenance and test procedures, lightening flashes during thunderstorms, and a wide variety of other phenomena. As impulse noise is short in duration ( 1 / 100 of a second, or so); it has little effect on voice communications, but can cause bit errors in a data transmission. See also noise.