Dolby Noise Reduction System - Nakamichi LX-5 Owner's Manual

Dolby Noise Reduction System
This deck uses the Dolby noise reduction (NR)
system, but with a difference: In addition to
the Dolby B-Type noise reduction built into
conventional cassette decks, it incorporates
the newly developed Dolby C-Type noise
reduction system.
Whereas the Dolby B-Type NR reduced noise
in the high frequencies by about 10 dB, the
Dolby C-Type NR with new characteristics
achieves an improvement of about
20
dB in
the range from 2 kHz to 8 kHz, where noise is
most readily audible.
The operating priciple of the Dolby C-Type NR
is similar to the B-Type, in that it does not
affect high-level signals in recording, but
processes only low-level signals in the mid
and higher frequency range. However, the
operation of the C-Type system starts at a
point 2 octaves lower than with the 6-Type
system, and it incorporates new circuits to
prevent encode/decode errors or high
frequency loss due to tape saturation. By
using the Dolby C-Type NR, dynamic range is
greatly enhanced and the setting of record
levels becomes easy and trouble-free.
This deck incorporates both the Dolby 6-Type
and the Dolby C-Type noise reduction
systems. When playing back a tape from your
collection which was recorded with the
B-Type NR "on", the NR switch should be set
to the "B-Type" position. When playing a tape
recorded with the C-Type NR, the switch
should be set to the "C-Type" positiod.
Note:
-
This system does not reduce any noise
already contained in the incoming input
signal. You should therefore strive to use
signals as noise-free as possible as a
recording source.
To the ear, the Dolby C-Type NR system
provides a constant noise reduction with any
type of music, during signal as well as during
silent passages. Modulation or breathing
noise has been suppressed past audibility,
and the tape's saturation level is increased by
the action of the so-called "spectral skewing
circuit" to determine pre-emphasis and de-
emphasis, and the "Anti-Saturation Network
(ASN)", etc.
Chart A illustrates the low-level encoding
characteristics for the 6-Type NR and the
C-Type NR. Decoding is done with exactly
opposite characteristics, thus achieving flat
overall frequency response. As can be seen
from the chart. the operation threshold of the
C-Type is two octaves lower than that of the
B-Type, and in the high frequency range,
noise reduction is by 20 dB.
Chart B shows an example of actual
frequency response and noise spectrum
analysis as recorded on a cassette deck. It is
evident from the noise spectrum analysis that
with the C-Type NR, noise is considerably
lower than with the B-Type and that it is
reduced by about 20 dB in the range from
2 kHz to 8 kHz. In addition, with the C-Type
NR the ANS and skewing features etc. serve
to increase high frequency MOL during high-
level recording.
Dolby NR Switch Operation
When a Dolby noise reduction system is to be
used, set the On/Off button (left button) of the
Dolby NR switch (1 5) to "On" and select the
desired system with the C-Type/B-Type
button (right button).
-Dolby NR-
n On C-Type
a
Off 6-Type
- 1
+
W ~ y p e NR to be used:
1
C-Type NR to be used:-
\
- . . . ,
I
--.
Dolby NR to be used:
-
Dolby NR not to be used:
1
Low-level Encoding
Characteristics
(-60 dB)
Frequency(H2)
I
Chart A
Frequency Response and Noise Spectrum Analysis
1
Chart B