JVC KD-D30 - Page 4

KD-D30 A/B/C/E/J/U |
No. 4209
Description of New Technology
Dolby C-type Noise Reduction System
—A newly developed IC is used to reduce noise and expand the MOL (maximum output level) dramatically. —
The Dolby C-type closely resembles the B-type in opera-
tion, the system compatible with ANRS, yet offers even
better performance and more distinctive features. Namely:
¢ Noise reduction is greater —20 dB from 1 kHz to
10 kHz and as much as 15 dB at 500 Hz.
e At 10 kHz it improves MOL by 4 dB when recorded at
OVU.
e It is immune to undesirable side effects such as modula-
tion noise and breathing.
Dolby C noise reduction solves the problem of achieving a
large amount of compression and expansion without in-
troducing undesirable side effects by the use of two pro-
cessing stages in series, each supplying 10 dB of compres-
sion during recording and of expansion during playback.
These circuits operate at independent levels. One, iden-
tified as the high-level stage in Figure B, is sensitive to
signals at about the same levels as Dolby B-type noise
reduction, while the other, the low-level stage, operates on
signals of somewhat lower level. Because the two stages
operate in tandem with each other, their effect is to multip-
ly the signals (or add and subtract in dB’s), so that a total of
20 dB of compression and expansion, and thus of noise
reduction, is accomplished. Yet simultaneously, at no time
is the signal subject to the vagaries of a single compression
or expansion action of 20 dB. In other words, the tandem
two-level, two-stage configuration provides a much more
accurate control of the signal than a single compander cir-
cuit would be able to achieve.
Since a single newly developed IC is used for Dolby C noise
reduction in this unit, compared with the Dolby B ICs two
normally used, better characteristics are achieved.
1. Recording/playback mode and NR mode (OFF/Dolby B/
Dolby C) selection is electronic.
2. The circuit does not need adjustment.
3. The over-shoot and limiter level specified for Dolby B
and C are adopted to give better transient characteri-
Stics.
4. Phase distortion is improved by use of a full-wave rec-
tifying circuit.
5. Almost totally integrated with few external com-
ponents.
6. With all signal processing performed in a single chip,
characteristics in recording and playback are inden-
tical.
7. Since the same elements are used for spectral skewing
and in the anti-saturation network in both recording
and playback, the characteristics are the same.
8. Multiplex buffer amplifier built-in.
9. External semi-fixed resistor allows setting of monitor
output level to required level.
10. Since the performance of the unit is not affected by
the side chain when noise reduction is switched off,
distortion and frequency response do not deteriorate.
11. It can be used as two Dolby B noise reduction circuits.
Other developments
In addition to two-level processing, Dolby C-type noise
reduction incorporates a number of further innovations.
Two of these, shown in Figure B as anti-saturation and
spectral skewing networks, are carefully calculated fre-
quency response modifications introduced in the encoding
(record) process and reciprocally compensated for in the
decode (playback) process. Their purpose is two-fold: to
further guard against audible side effects, and to ensure
the practicality of the system in day-to-day consumer use.
The specific benefits of these innovations include the
reduction of encode-decorde errors and a reduction of
upper-middle and high frequency tape saturation and its
side effects, such as high frequency losses and _ inter-
modulation distortion. Together with the two-level, two-
stage configuration, these new developments result in a
20 dB noise reduction system at least as free of side
effects as the 10 dB B-type system, and one which is just
as practical in day-to-day use.
9
10 20 Hz SO 100 200
1000 2000 $000 10000 = 20000
Fig.
4-A
Low-level
encoding
frequency
response
a en