Akai M-7 - Page 3

II
HOW
TO
MEASURE
DESIGNATED
VALUES
IN
SPECIFICATIONS
TAPE SPEED
DEVIATION :
WwOwW AND
FLUTTER :
FREQUENCY
RESPONSE :
(OVERALL FREQU-
ENCY RESPONSE)
Record the 1,000 cps. sine curve of
the tape speed at rating speeds
with a standard sound recorder
(AMPEX 351A, for instance) which
is little affected by the tape speed
deviation throughout the whold len-
gth of the tape. Put this standard
tape on the tape recorder under
test for playing back, and measure
its output by a counter, then con-
vert the value into rating power fre-
guency to evaluate the tape speed
deviation.
For a rough measurement, the tape
speed deviation can also be measu-
red with a speed test timing tape by
the count on a stop watch.
Playback the 3,000 cps. standard
tape that guarantees wow and flut-
ter within 0.07 per cent, and read
the effective value on wow meter.
Since the sensibility of wow and
flutter frequency below 2 cps and
above 5 cps drops, the frequency
over 5 cps is put to 3 db/OCT cir-
cuit, and the frequency below 2 cps
is put to 6 db/OCT circuit for adjust-
ment. This adjusted value is called
auditory compensated value.
Connect to the input terminal of the
test recorder a sweep frequency of
the level-20 db.
signal, playback the tape, terminate
Record the sweep
the output with eight ohms.
Read the frequency response which
should have a maximum deviation
of 6 db.
TOTAL HARMONIC
DISTORTION
FACTOR :
SIGNAL TO
NOISE :
OUTPUT
CROSS TALK
Provide
the
input
terminal
of
the
tested
recorder
with
1,000
cps
sine
curve
signals
and
record
these
sig-
nals
ona
recording
tape
ait
the
zero
level
on
the
recorder’s
internal
VU
meter.
Then
playback
the
signals
under
the
normal
recording
condi-
tion
to
measure
the
distortion
factor
by
an
oscillator.
Remove
the
recor-
ding
tape
from
the
recorder,
then
read
the
noise
level
on
the
oscillator
to
get
the
required
distortion
factor
by
the
following
formula
:
dOQ=d-—dl-—d2
dO---required
d---overall
distortion
factor
bl--noise level
d2---distortion
factor
of
the
oscilla-
tor used
Playback
the
sine
curve,
250
cps
tape
recorded
on
a
standard
recor-
der
on
the
tested
recorder
to
measure
the
voltage.
Remove
the
tape,
then
measure
the
noise
level
under
the
same
condition.
Calculate
the
ratio
between
the
two
in decibel.
Playback
on
the
test
recorder
the
1,000
cps.
sine
curve
tape
which
was
recorded
at
the
zero
VU
level
on
a
standard
recorder.
Terminate
the
test
recorder
with
eight
ohms.
Square
the
voltage
reading,
then
divide
the
figure
by
eight
ohms
to
get the rm.s. power output.
Record
1,000
cps
signal
at
+
3VU
on
the
third
track,
then
playback
this
signal
thru
a
1,000
cps.
Band
Pass
Filter.
Compare
the
output
of
tracks
1
and
3
in
decibels.