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4-Track Record/Playback:
After recording or playing back one
side of the
cassette,
remove
the tape by depressing
the Eject button
5),
turn the
cassette
over and insert it again.
Then, the tape can
be used
again for
the same
time as the first side.
Music
is composed
of sounds
of different.
loudness separated by intervals of silence.
Loud and soft sounds are here shown as long
and short lines.
The music shown
in 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 cassette tapes, tape noise is
much more noticeable than it is in professional
tape recordings, although even there it is a
problem.
3. Music and Noise
When a tape recording is played, noise from
the tape obscures the quietest musical sounds
and fills the silence when no sound should be
heard at all. Only when the music is loud the
noise is not usually heard; however, tape noise
is so different from music that it sometimes
can be heard even then.
20
Before
the recording
is made,
the
Dolby
System
"'listens" to the music to find the
places where a listener might later be disturbed
by hiss from the tape.
This happens mainly
during the quietest parts of the music.
When
it finds such a passage, the system
auto-
matically increases the volume so that music
is recorded at a higher level than it would be
normally.
2. The Recording
In a Dolby System recording the parts of the
music which have been made louder stand
out clearly from the noise.
Thus recordings
sound
brilliant
and
unusually
clear
even
when played back without the special Dolby
System circuit.
3. What the Dolby System does
during playback
When tapes are played on a high-fidelity tape
deck
equipped
with
the
Dolby
System
circuit, the loudness is automatically reduced
in all of the places at which it was increaseed
before recording.
This restores the music 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.
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