Hitachi D-900 Bedienungsanleitung Seite 19

GENERAL INFORMATION «
HOW THE DOLBY NR SYSTEM WORKS
Making an ordinary recording:
1. Music.
Music is composed of
sounds of different loud-
ness separated by inter-
vals of silence.
Loud and soft sounds are
here shown as long and
short lines. The music
shown by this diagram
starts loud and gradually
becomes very quiet.
2. Noise.
Any recording tape, even
of the best kind, makes a
constant hissing noise
when played.
At the very slow speeds
and narrow track widths
used in tape cassettes,
tape noise is much more
noticeable than it is in
professional tape record-
ings, although even there
it is a problem.
Making a Dolby system recording:
Dw
1. What the Dolby
System does first.
Before the recording is
made, the Dolby System
listens'' to the music to
find the places where a
listener might later be
from the tape. This hap-
pens mainly during the
quietest parts of the mu-
sic' When it finds such a
passage, the system auto-
matcially increases the
volume so that music is
recorded at a higher ievel
than it would be normally.
2. The Recording.
In a Dolby System record-
ing the parts of the mu-
sic which have been made
louder stand out clearly
from the noise. As a re-
cordings sound brilliant
and unusually clear even
when played back. without
the special Dolby System
circuit.
3. Music and Noise.
When a tape recording is
played, noise from the
tape obscures the qui-
etest musical sounds and
fils the silence when no
sound should be heard at
all. Only when the music
is loud the noise is not
usually heard; hcwever,
tape noise is so different
from music that it some-
times can be heard even
then.
3. What the Dolby
System does during
playback.
When tapes are played
on a high-fidelity tape
recorder equipped with
the Dolby System circuit,
ically reduced in all of the
places at which it was
increased before record-
ing. This restores the
musci to its original
level again.
At the same time, the
noise which has been
mixed with the music is
reduced in level and this
is by the same amount
usually enough to make
it inaudible.
When you are connecting it with other units which produce a high volume
of leakage flux, hum may be induced into this unit, so stack the units
with sufficient spacing between them. When there is a slight bias
leakage, noise may occur during AM reception. If this is the case, keep
the unit as far from the tuner as possible.
English 9