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4.4
Channel Separation
Since the stereo coder uses a digital technology,
there is not any kind of adjustments controls for
stereo separation. A good measurement set like
the BELAR (USA) model FMS-2, will be needed.
If you do not have an excellent measurement set,
please do not intend this measure.
Note :
This measure must be done with stereo coder
inputs disconnected from audio processor. Then the
jumpers JL & JR must be open.
a) Connect the BELAR measurement set to the
MPX output connector.
b) Check the PHASE mode of the Belar. You
must get at least – 65 dB rejection of 19 KHz
pilot tone. If not, please make the Belar
calibration procedure of PHASE (see Belar
manual)
c) Connect a sine wave generator at 400 Hz, 1V
RMS
to
the
Left
disconnected the right input JR.
d) Measure channel separation at the Belar. Right
channel. It will be better than 60 dB
e) Now, connect the sine wave generator, at the
same frequency and level, to the Right
Channel (pin JR).
f) Measure at the Belar the residual level of the
Left channel. It will be better than 60 dB.
g) Verify channel separation at the 20 Hz –
12.000 Hz range This must be better than 50
dB (60 dB typical).
4.5
Measurement of Residual Noise
Open the jumpers JL & JR.
Use a good Audio Voltmeter with A weighted filter
connected at the Left and Right audio outputs of
the BELAR modulation monitor. Use as reference
4 Vpp sine wave.
Values better than 92 dBA must be measured (94
dBA is typical value)
SOLIDYNE
Input
(JL).
Leave
AudiMax 362
4.6
Audio Distortion measurements
Connect a good distortion measurement set like
System ONE or Sound Tech ST 1710A to the Left
& Right audio outputs of the BELAR set. Values
under 0,01 % must be measured at 1 kHz
Since Belar has it distortion floor at 0,01%, in
order to measure the real distortion of 362 stereo
coder, is recommended to use a procedure not
based on modulation monitors.
Proceed this way:
a) Connect to ground Test Point TP1 in order to
cancel 19 KHz Pilot
b) Then, connect a very low distortion audio
generator at both inputs JL & JR. This will
cancel 38 Khz subcarrier. Connect a good
THD distortion measurement set at the MPX
output of stereo coder. Adjust to minimum
value the THD meter.
c) Use
the
monitor
measurement set to analyze the distortion
products in order to separate 38 KHz residual
and noise from the distortion components. Use
a Tektronix 5L4 N analyzer, or TiePie FFT
HS3 probe, or SoundTech Lab software, etc.
Identify the harmonics of 1 KHz and calculate:
100
Distorsión
=
×
1
H
H1 = Level of fundamental tone.
Hn = Level of harmonics (reduced by the
gain set of the THD meter).
Verify that the distortion level is under 0,003 % at
1 KHz.
output
of
the
THD
(
2
2
2
H
2
+
H
3
+
H
4
+
Κ
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