Double Noise Reduction System - Nakamichi 1000 Operating Instructions Manual

Double Noise Reduction System
The Nakamichi 1000 incorporates the 2
Famous Noise Reduction Systems, namely
the Dolby Noise Reudction System and
DNL (Dynamic Noise Limiter) developed
by Philips, which enable to surpress
unimaginable noise level.
Dolby NR
Your Nakamichi 1000 incorporates the
Dolby Noise Reduction System (under
license from Dolby Laboratories, Inc.)
originally developed to produce a master
tape from which to cut records with a high
signal-to-noise ratio.
Noise heard from a recorded cassette
primarily comprises tape noise and the noise
produced by the playback equalizer
amplifier of the cassette tape deck, and is
largely distributed over a 2KHz to 10KHz
range. Such noise can be effectively reduced
by amplifying signals within this range at the
time of recording, then attenuating them in
playback, through a process as illustrated in
Fig. 1.
INPUT — PREAMP. -| DOLBY | REC.AMP.
= cg en ae C _. PLAYBACK __
EQ. AMP.
— PREAMP. - OUTPUT
Fig.1 Record/Playback Process
This treatment is given to such signals
regardless of their strengths, however, strong
high-frequency signals cannot be recorded.
So it is necessary to change the gain of this
Briel & Kyeer
Briiel & Kicer
Copenhagen
Potentiameter Range' dB Rectifier:
Lower Lim Freq:
special circuit with respect to the strength of
the high-frequency signals. The Dolby
circuit makes this possible.
For instance, if high-frequency signals of
—40dB enter the Dolby circuit from input
terminals, it delivers signals of —30dB for
recording on to the tape. Conversely, if
high-frequency signals of —30dB enter the
same circuit from the playback head (Fig. 2),
it delivers signals of —40dB for reproduction
from the stereo amplifier.
Thus input/output signals are attenuated by
10dB, with equivalent reduction in the level
of tape noise and equalizer amplifier noise.
The circuit is designed so that it does not
affect signals of —5dB or greater.
Input Signals
-30
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1
1
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1
1
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4
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1
sjeuBig jnding
PLAY
Amplification & Attenuation at 4KHz
Fig.2 Working Principle of Dolby NR Circuit
As is clear from the foregoing explanation,
the signal-to-noise ratio of sound improves
by about 10dB if it is recorded and
Briel & Kjoee Britel & Kjaer
Hz Wi Speed —.__ mm/sec Paper Speed:____ mm/sec.
sasites dB ABI
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40-207
Measuring Obj: fT
af
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Dolby NR out:
OP 1124 Multiply Frequency Scale by
=== Dolby NR + ONL Eps
40000 20000
(1632/2012)
reproduced through the Dolby circuit,
enabling you to enjoy clean, transparent hi-fi
stereo sound. This system is international,
and recordings made under it can be
reproduced by any cassette or reel-to-reel
tape decks equipped with the same system,
regardless of their makes.
DNL (Dynamic Noise Limiter)
= we a T) roe eS
- eae
Fig. 4 DYNAMIC NOISE LIMITER : Steady-state characteristics.
Parameter : Level Vi in dB, Od} = 780mvV.
When set to "On", DNL operates only whiie
playback. It also operates at Source Monitor
but has nothing to do with recording. As
shown in the above Fig, DNL serves
lowering more noise where level is low, it
further decreases noise while the Dolby NR
and S/N Ratio are in the preferable
condition.
The detailed data are shown below for your
ready perusal wherein dewease of only 3dB
will result in a great effeci from the acoustic
standpoint.
It also gives an effect when hiss noise or
scratch noise is noted fron the source.
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