Akai GX-F44R

14
Output level (dB)
-40 -30 -20 -10 0 +10
Input level (dB)
Fig. 13 Input Characteristic of Dolby C-type NR
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Frequency(Hz)
Response (dB)
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Fig. 14 Encode Characteristic of Dolby C-type NR
4 6 810K 20K
Epaduency (5)
Fig. 15 Encode Characteristics of Dolby B-type and C-type in low level
The signal inputted into the next low level stage is
again separated into the main pass route and the side
chain route, and the 2nd encoding is carried out.
The encode characteristic in the low level stage is
same as the characteristic of the high level stage
except that its compression starting level (threshold
level) is lower, and as a result, the signal stressed by
about 20 dB from middle to high frequency of the
low level appears at the output terminal.
Figs. 13, 14 and 15 show the input/output character-
istic, encode characteristic and encode characteristics
of B-type and C-type in low level, respectively. As
shown in Figs. 13 to 15, C-type is limiting the high
frequency when recording. This is done by the
spectral skewing circuit provided in the encoder input
and by the antisaturation circuit. The skewing circuit
prevents the processing error by deemphasizing the
frequency of 10 kHz or more which is unstable for
the cassette deck and by reducing the noise reducing
operation. As a result, the signal modulation due to
the high frequency component can be prevented.
The antisaturation network operates only on the large
amplitude signals of more than 2 kHz and reduces
the high frequency saturation of the tape.
These are completely complementary in the encoder
and decoder and make possible the MOL improve-
ment of about 8 dB at 15 kHz. In decoding, the side
chain route is combined in opposite phase with the
main pass route and the characteristic opposite to
that of the recording is obtained. The high frequency
signal limitation by the skewing circuit and anti-
saturation circuit is released in decoding. C-type can
be easily switched to B-type, and to use it as B-type,
switch off the encode (or decode) of the low level
stage and change the constant of the high level stage
(to make encode or decode characteristic).
At that time, switch off the skewing circuit and
antisaturation circuit.