Since the calibration is extremely stable and
should
not
have
to
be repeated (except
to
period-
ically check
it),
we
suggest
that
you mark
the
settings
of
your
recorder's
output
level controls
with
a felt-tipped pen. Doing so
will
enable
you
to
easily reset the controls
if
they are
inadvertantly moved.
PROCEDURE FOR RECORD
CALIBRATION
Before proceeding
with
the record calibration,
be certain
that
the playback adjustments have
been performed. DO
NOT
CHANGE TH E POSI-
TIONS OF THE RECORDER'S
PLAYBACK
LEVEL
CONTROLS
(if
any) OR
THE
4270's
PLAY
CAL
CONTROLS.
In
the
event a record calibration is performed by
the use
of
TAPE MOI\IITOR 1 IN and
OUT
Jacks
of
Model 4270,
shift
the SELECTOR switch
to
TAPE 2 after turning on a 400Hz TONE knob.
On the other hand, when the record calibration is
conducted by the use
of
TAPE
MONITOR
2 IN
and
OUT
Jacks,
shift
the SELECTOR switch to
TAPE
1. Home-position the SELECTOR switch
after the calibration.
For Recorders
with
Three Heads
1. Thread a blank tape
onto
your
recorder (or
insert a cassette).
2. Put the 4270's
DOLBY
Switch in the
"PLAY"
position.
3. Put both the 4270's and the recorder's moni-
tor
switches in
the
"Tape"
position.
4. Put the 400Hz TONE Switch in
the
"ON"
(in) position.
5. Commence recording.
6. Adjust the recorder's record level controls
so the tone
will
deflect the 4270's
SIGNAL-
STRENGTH
lVIeter
to
the
"DOLBY
LEVEL"
mark.
For Recorders
with
Two
Heads
1. Thread a blank tape
onto
your
recorder (or
insert a cassette).
2. Put the 4270's
DOLBY
Switch in
the
"OFF"
position.
3. Put the 400Hz TONE Switch in the
"ON"
(in) position.
4. Commence recording.
5. Adjust
the
recorder's record level controls
to
deflect the recorder's meters
to
OVU.
6. Record the tone
for
approximately 15
sec-
onds.
I
7. Stop the recorder and rewind
it
to the begin-
ning
of
the
tone recording.
I
8. Put the 4270's
DOLBY
Switch in the
"PLAY"
position.
I
9. Put the recorder in the play mode and play
back the tape.
10. Note the level reading on the 4270's SIG-
NAL-STRENGTH Meter. To check the left
•
channel level,
put
the METER Switch in the
"OUT"
position. To check the right chan-
nel level,
put
the METER Switch in the
"1
N"
position. The object is
to
adjust the
recorder's record level controls so the play-
back level achieved indicates
"DOLBY-LEV-
EL"
on the 4270's SIGNAL-STRENGTH
Meter.
11.
If
the Meter indicates
"DOLBY
LEVEL"
,
calibration is completed.
12. A)
If
the Meter indication is above the
"DOLBY
LEVEL",
repeat steps 2 - 11,
but
decrease
the record level in step 5
to
slightly below OVU on the recorder's
VU Meters.
B)
If
the Meter indication is below the
"DOLBY
LEVEL",
repeat steps 2 - 11,
but
increase the record level in step 5
to
slightly above OVU on the recorder's
VU Meters.
For all Recorders
After
the
"DOLBY
LEVEL"
has been achieved
on the SIGNAL-STREI\lGTH Meter, DO NOT
change the recorder's
input
or
output
level con-
trols or the 4270's
PLAY
CAL
controls.
Utilizing the recorder's VU Meters, proper Dolby
recording levels are adjustable by using the RE-
CORD
LEVEL
controls on the
front
panel
of
the
4270. This
only
applies when making a Dolby
recording.
Setting the level slightly
lower
than OVU
will
increase the
Dolby
effect.
CHANGING THE RECORDER'S RECORD OR
PLAYBACK
LEVELS
OR
THE
4270's
PLAY
CAL
CONTROLS WI
LL
AFFECT
THE
DOLBY
CALIBRATION
.
15
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