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Double Noise Reduction System
The Nakamichi Tri-Tracer 1000
incorporates
special
circuit
with
respect
to
the
strength
of
reproduced
through the Dolby
circuit,
the
2
Famous Noise
Reduction
Systems,
the
high-frequency
signals. The
Dolby
enabling
you
to
enjoy
clean,
transparent hi-fi
namely
the
Dolby
Noise
Reduction
System
circuit
makes
this
possible.
stereo
sound.
This
system
is
international,
and
DNL
(Dynamic
Noise
Limiter)
for
instance,
if
high-frequency
signals
oí
and recordings
made
under
itcan
be
developed
by
Philips,
which
enable
to
supress
-30d8
enter
the Dolby
circuit from
input
reproduced
by
any
cassette
or
reel-to-reel
Your Tri-Tracer 1000
incorporates
the
same
circuit from
the playback
head
(Fig.2).
Dolby
Noise
Reduction
System
(under
it
delivers
signals
of
-30d8 ïor reproduction
DN L
license
from Dolby
Laboratories,
lnc.)
from the
stereo amplif
ier.
originally
developed
to
produce
a
master
Thus
input/output
signals are
attenuated by
tape
from
which
to cut
records
with
a
high
l0dB,with
equivalent reduction
in
the
level
signal-to-noise
ratio
of tape
noise
and equalizer
ampliíier
noise.
Noise
heard
Írom
a
recorded
cassette
The
circuit
is
designed so
that
it
does
not
primarily
comprises tape
noise
and
the
noise
afÍect
signals
of
-5dB
or
greater.
unimaginable noise
level.
Dolby
NR
produced
by the playback
equalizer
amplif ier
of the
cassette
tape deck,
and
is
largely
distributed
over
a2KHz
to
10KHz
range.
Such
noise
can
be
eÍfectively
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.
tNpUr
*
pREAMp.
* Folerl -
REc.AMp.
/'
- -{
- I _ l-
-PLAYBAcK
--
--\_ )
-\_
Eo.
AMP.
fDoLBI
-*
PR
EAMP.
-
ourPUT
Fig.l
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
lnput
Signals
I
I
;
,y
v
Amplification & Attenuation
at
4KHz
Fig.2
Working Principle
of
Dolby Circuit
As
is
clear
Írom
the
foregoing explanation,
the
signal-to-noise
ratio
oÍ sound
improves
by about
10dB
iÍ it
is
recorded
and
terminals,
it
delivers
signals
of
-20d8
for
tape
decks
equipped
with
the
same system,
recording on
to
the
tape.
Conversely,
if
regardless
of their
makes.
high-frequency
signals
of
-20d8
enter
the
DYNAMIC NOISE
LIMITER
I
Steady-state
char*t€ristics,
Psrsmeter
:
Lwel
vi
in
dB,
O
dB =
7a0 mV,
When set
to
"On",
DNL
operates
only
while
playback.
lt
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
decrease
of only
3dB
will
result in
a
great
effect
f
rom the
acoustic
standpoi
nt.
It
also gives an
effect when
hiss
noise
or
scratch noise
is
noted
from
the
source.
Bruel &
Kier
at
E
i'-;t"i'
e oI
É
1,.,
B::"1"
I
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- ]
:*
PolèhnomererRange
-
-dg
Recinè'
L.werLim Freq:
--E:
W, Speed
Pap.'Speed -
am/sp:
Mu
r:pL FÍ.quenc!
Só1 d
.r
10
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