Barkhausen effect

The tendency of the magnetic elements or domains on a magnetic medium to influence one another and to become magnetized in one direction or another as a group rather than individually. This means that a magnetic medium, such as recording tape, has a graininess in its magnetic makeup which is what causes most background noise, or tape hiss. Modulation noise, which is only present in conjunction with a recorded signal, is also caused by the Barkhausen effect, and is sometimes called Barkhausen noise.