Audio Engineering

752 Chapter 26

ferrous material remains magnetized with the residual induction B4. This remaining force
is referred to as remnance. For this remnance to be neutralized, an opposite magnetic
force must be applied, which accounts for the rest of the looped curve in Figure 26.3.
The magnitude of the applied magnetic force required to reduce the remnance to zero
is termed coercivity (the ideal magnetic tape exhibiting both high remnance and high
coercivity).

26.4 Bias........................................................................................................................

If a sound recording and reproduction system is to perform without adding discernible
distortion, a high degree of linearity is required. In the case of tape recording this
implies the necessity for a direct relationship between the applied magnetic force and
the resultant induction on the tape. Looking again at Figure 26.3 , it is apparent that the
only linear region over which this relationship holds is between B1 and B2, with the
relationship being particularly nonlinear about the origin. The situation may be compared
to a transistor amplifi er, which exhibits a high degree of nonlinearity in the saturation
and cut-off region and a linear portion in between. The essence of good design, in the
case of the transistor stage, is appropriately to bias the amplifi er in its linear region by
means of a steady DC potential. And so it is with magnetic recording. In principle, a
steady magnetic force may be applied, in conjunction with the varying force dependent

H H

B

B

O

B1

B2

B4 B3

Figure 26.3 : BH curve.