Used in recording signals on a magnetic media (tape). As the tape passes the recording head, the head generates a varying magnetic field corresponding to the analogue signal to be recorded. The problem is that if the magnetising force is in the form of a sine wave, (with excursions either side from zero), the resulting flux is non linear due to hysteresis and the wave form becomes distorted. The way we get round the problem is to apply a bias. This is accomplished by using a d.c. offset to magnetise the tape to halfway up the initial magnetisation curve. It is then important that the amplitude of the signal remains within the linear part of the magnetisation curve to avoid distortion. Alternatively an a.c. bias is applied, where the a.c. bias is of a much higher frequency than the signal to be recorded.
Difference of potential applied to a vacuum tube or transistor to establish a reference operating level.
Persistent tendency for the measurements, as a group, to be too large or too small.