Answer 5—There is a characteristic curve associated with magnetic recording materials that relates the applied magnetic field to the field that remains in the material after the external field is removed. This curve is highly nonlinear in the center and at the ends, but it usually exhibits two relatively linear regions on either side of center.

A bias signal is added to any signal (such as audio) that needs to be recorded with low distortion in order to keep the system operating in the linear portion of the medium’s transfer curve. Digital recording, such as that used in computer disk and tape drives, isn’t concerned with the linearity of the recording process, and therefore doesn’t require bias.

Contributor: David Tweed