Akai GX-F44R

12
INPUT
OdB
-60
High level signals
(no dynamic action)
Dynamic action
of high-level stage
Dynamic action
of low-level stage
Low level signals
(no dynamic action;
amplifier action only)
Fig. 11 Operational Region of each Processor
one signal is just outputted via the Main Pass and
another signal going through the Side Chain is
produced separately as the noise reduction signal and
added to the output. For this reason, the NR signal
component included in the output signal can be kept
to minimum.. Fig. 11 shows the operational region of
each processor. As one major feature, the C-type can
improve the high frequency characteristic. Man’s
audio sensitivity decreases a lot at 10 kHz or higher,
and this means that NR amount in this band can be
relatively small.
For this reason, the C-type has two additional
circuits, spectral-skewing circuit and antisaturation
network. In the spectral-skewing, the NR operation
of more than 10 kHz is weighted by the LC circuit of
12 dB/oct. and reverse compensation is made at the
time of decoding, and the high frequency linearity is
improved to the extent that the compression amount
is reduced. The anti-saturation network has a func-
tion to reduce the Rec level by about 3 dB for the
high level high frequency signal only, and the distor-
tion rate in high band is improved.
3. CIRCUIT OPERATION
Fig. 12 (a) shows the basic NR circuit structure of
Dolby C-type.
The encoder and decoder of C-type respectively
consist of two stages (two Dolby B-type processors
with the external constant changed) called high level
stage and low level stage. In recording, the input
signal enters the high level stage via amplifier (A1),
spectral skewing circuit, MPX filter and amplifier
(B1). Then, like B-type, the signal is separated into
the main pass route and side chain route. In the main
pass route, the signal just goes to the adder (EK), and
in the side chain route, only middle and high fre-
quency signals of low level are passed by the variable
filter. Then, the output from the side chain route is
combined by the adder (EK) with the signal of the
main pass route to obtain the 1st encode (compres-
sion) characteristic, and in the low level stage, too,
the stressed signal from middle to high frequency
(10 dB in the vicinity of 1.5 kHz) is sent to the next
low level stage. The operation in the high level stage
is similar to that of B-type except when the turnover
frequency of the encode characteristic is on a lower
side (below 2 octave).