Technics SH-9020 - Page 3

=m ABOUT PEAK-LEVEL METERS AND
VU METERS
In order to faithfully transmit music signals that are
short in duration, signals which include a great many
“pulsing’’ sound components with high peak values and
which invariably change in complex ways, every signal
level in the system must be monitored as precisely as
possible. For this purpose the VU meter—which indi-
cates the average value of the signal level—and the
peak-level meter — which indicates the peak value of the
signal — have been used.
The VU meter and the peak-level meter function with a
fundamentally different character, and each has its own
superb features. Thus, in order to monitor the system at
the highest possible level of precision, it is necessary to
use these two types of meters correctly, depending
upon the application and purpose, by using their re-
spective features to maximum advantage.
VU meters..... What they are and do
VU meters indicate the average value of the signal
waveform (with an ‘‘attack”’ time of about 300msec),
and are designed so that the indication needles move in
very close relationship to the perception.of sound
volume.
VU meters are convenient for monitoring sound volume,
and are especially convenient when used for monitoring
the levels when mixing various signals which have
different peak values, thus making it possible to perform
the mixing without differences in the volume level.
Because the meters In this unit— when used as average
meters— function with performance which is equal to
that of VU meters which have an “‘attack’’ time of 330
msec and a recovery time of 25Omsec, they can be
used to check the level in the same way as VU meters.
Note, however, that, for VU meters, 0 VU indicates a
signal level of 1.228V at 600, but, when the meters of
this unit are used as average meters, the — 16dB point
is equivalent to O VU (with the meter sensitivity selection
pushbutton set to OdB).
Peak-level meters..... What they are and do
Peak-level meters are designed to indicate the peak
value of the signal waveform, and, because they must
be able to precisely indicate the peak values even of
short, “‘pulsing’’ sounds of short duration, they have
extremely fast response characteristics.
In order to faithfully transmit such signals as music
signals, which include a great many peaks, it is neces-
sary to monitor the peak values precisely, and they are
especially indispensable meters for effectively making
use of the peak factor of audio equipment.
The meters in this unit—when used as_peak-level
meters — have an especially fast response characteristic,
with an “‘attack”’ time of 100«sec, resulting in precise
indication
of
virtually
OdB
with
relation
to
an
input
signal of 10kHz, single wave.
= ABOUT PEAK HOLD
“Peak hold” is a feature which permits the meters to
continuously indicate the maximum peak value detected
by the peak meters. This system is designed so that it
requires 25 minutes or more for the indication to return
from OdB to —3dB under no-signal conditions.
In order to most effectively take advantage of the peak
factors of audio equipment, it is necessary to be able to
precisely determine the maximum peak value of the pro-
gram source. The peak-hold feature, therefore, makes it
possible to continuously maintain the maximum peak
value of signals such as music — with constantly chang-
ing peak values — at the complete value for a long period
of time, thus making it possible to pre-set to the correct
recording level before beginning to record.
@ Peak-hold response characteristic
e As explained previously, the peak-hold feature can be
used to maintain the indication of the maximum peak
value of the program source for 25 minutes or more.
This makes it possible to get the indication of only the
peak signal, even for signals in which there are com-
plex changes in the peak value.
-Peak-hold response
Signal waveform
e As can be seen from the figure above, it is possible to
use this feature to visually determine the maximum
peak value easily, because the peak value indicated
first continues to be indicated until a higher peak
output is detected, and so on.
SH-9020
ron ation vonmnioene
m
ABOUT
THE
INDICATED
VALUES
20 10
AO 30 0 +10
dB SCALE
W SCALE
-0
Ssro01 01 1 10 100
0.
dB
peak /average
@ Indication of decibels (dB)
e The outer (upper) scale is calibrated in dBm units and
defines the signal level of 0.775V (1mW) at 6002 to
be OdB. When the meter sensitivity selection push-
button is set to OdB, the meters will indicate —20dB
at an input of OdBm. When the pushbutton is set to
+20dB, the meters will indicate OdB at an input of
OdBm.
For VU meters, an indication of O VU indicates a
signal level of 1.228V at 6009. For this unit, how-
ever, the —16dB point becomes equivalent to O VU
(when the meter sensitivity selection pushbutton Is
set to OdB).
The relationships between dBm, dBs, VU and voltage
are shown below.
* At the level usually used, a 1V signal level is de-
fined to be OdBs.
Value indicated by meters (meter sensitivity: 0 dB)
+10 +30 24 5V
+20
+20 10
0 +20
+10
+10
—10 +10
0 1.228V
—20 0 0.775V
—30 —10
—20
—20 0.1
—40 —20
— 30
— 30
—50 —30 24 5mV
[4] SH-9020
e In addition to being used for checking the recording
level and the Output level, the dB scale can also be
used, by playing a frequency-check record, to check
the frequency response of a phonograph cartridge or
to check channel separation, etc.
@ W indication
e When this unit is used as a power meter, the inner
(lower) scale of the meters should be used.
The W scale is calibrated in output values at a pure
resistance load which is equivalent to nominal resist-
ance.
When the meter sensitivity selection pushbutton is
set to the OdB position, power is indicated in the
range shown (1mW ~1000W) on the meters. When
it is set to +20dB, the actual value of the power is
0.01 of the indicated value (thus, a range of 0.01
mW ~ 10W).
e Impedance correction
Because the values indicated on the meters (when
they are used as power meters) are different depend-
ing upon the impedance of the speakers used, It Is
necessary to use the speaker impedance selector (on
the rear panel) to make the impedance correction.
If the speakers to be used have an impedance of 8
ohms, set the switch to the 8 position. For
speakers with a 6-ohm impedance set to 6, and for
a 4-ohm impedance set to4.
Note that meter readings will be incorrect if the
correct setting is not made to correspond with the
impedance of the speakers.
Speaker impedance selector
* If the speakers have an impedance different from
any of those indicated, set the selector to the
closest approximate value.
Actual output is then calculated in the following
way: (Value indicated on meters) x (Selector set-
ting + Impedance of speakers used).
If, for example, the selector is set to 8 for speak-
ers of 16-ohm impedance, multiply the value indi-
cated on the meters by 1/2 to determine the actual
output.
* When the Technics models SE-9060 is used for
Balanced-Transformerless operation, set the speak-
er impedance selector to a value which is 1/2 of the
impedance of the speakers to be used.
If, for example, the speaker impedance is 82, set
the selector to the “49” position.
m= METER I
Because,
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e These figure
signal levels
level meter
meter at the
@ Sine wave
peak
@ Square wz
peak
© Music sig!
e As you can
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level meters
changed, bu
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of indicating