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9 . R E C O R D I N G B I A S A D J U S T M E N T
When recording, if only the recording signal is
applied to the head, the recorded signal distorts
because of the hysterisis characteristic. This can
be improved by applying a bias along with the
recording signal. There are two kinds of biasing,
DC biasing and AC biasing.
AC bias is superior to DC biasing in all important
factors such as recording sensitivity, distortion
figures, S/N and dynamic range.
o
Bias frequency should be over five times that
of the highest recording frequency.
Fig. 17 shows the relation between biasing degree,
output level, distortion and frequency response.
As the biasing degree increases.
1. The output
level increases gtadually, and
reaches the saturation leyel at a certain point.
2. When biasing more, the output level and
distortion decrease.
3. Frequency response varies according to the
biasing degree. High range increases with over-
biasing, and decreases with underbiasing. With
a proper amount of bias, it becomes flat.
- B
D C b i a s s y s t e m
+ B
S i g n a l
F i g . 1 6
az Proper Bias
+H
I
I
i
l
J
A C b i a s s y s t e m
t-
o
1
i
O u t p u
- -
7 /
---A1/
----\7-
(
il
"l
; l
r f
t(
r
F+
+ H o I
j t -
t n P u t > t 9 n a t
I n p u t S i g n a l
Fig-8 Zero bias system
6 '
!J.
3
4
I
I
------+ Bias level
--------+ Freouence
F i g . 1 7 - a
F i s . 1 7 - b
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