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2.1.4 More about noise: Expanders and Noise-Gates
A lot of instruments such as microphones, amplifiers, guitar pickups, etc generate some noise, either at low
frequencies (hum) or at high frequencies (hiss) such noise will inevitably interfere with the quality of your
audio signal. Now, if you scream into a microphone you will not hear the noise generated by such micro-
phone because such noise will be "masked" by the higher level of the signal, your voice in this case.
But if you sing into your microphone more gently in a soft passage, the level of the signal generated by your
voice will get much closer to the floor noise level and such floor noise will become disturbing. In order to kill
this problem Expanders and noise-gates are used. An expander is the opposite of a compressor: attenuating
the signal when the amplitude drops they can limit the floor noise.
Now, we do not need dramatic expansion of a signal across the range, This would generate a resulting dy-
namic range of over 150dB. For this reason the amplitude control will be applied only to those audio signals
which are below a set threshold. Those audio signals above the set threshold will not be affected. Noise-
gate can be regarded as a simple Expander. But the Expander will attenuate the audio signal continuously
below the set threshold while the noise-gate will simply dramatically cut-off the audio signal completely.
2.2 Voltage Controlled Amplifier (VCA)
The VCA is the soul of the ACL2 PRO and it is one of the best components available today in his category thanks
to its excellent performances in terms of distortion, linearity, noise and temperature stability.
2.3 Inputs
2.3.1 Take it easy: Balanced Inputs
To make your life easy and clean we have provided ACL2 PRO with electronically balanced inputs. Even if
you operate at high signal levels, hum and noise will be reduce automatically. There is also a servo-function
that will automatically adjust the internal level when unbalanced connectors are detected. The correction
if of 6dB and it will avoid differences in level in between input and output signal.
3. CONTROLS
THRESHOLD
0
SC EXTERANL
-35
-10
2.5
R
1.5
LTO
-60
7
-30
0
1.2
8
OFF
+15
-40
+20
dBu
1:N
SC MONITOR
dBu
THRESHOLD
RATIO
THRESHOLD
EXPANDER / GATE
Your ACL2 PRO presents with right and left channels. Each channel is equipped with the same control elements: 7 push-
button switches, 8 rotary controls and 26 LEDs. You can easily operate the stereo mode via pressing the Couple switch.
The details please refer to following content.
1. Couple Switch
Pressing this push-button for stereo mode operation.
When engaged, the Master channel (channel 1) will take control of both channels and override all the controls
and switches of channel 2 with the exception of the SC Monitor, SC External, SC Filter and Bypass switches as
well as the Peak Limiter control.
3.1 Expander/Gate Section
GAIN REDUCTION(dB)
INPUT / OUTPUT LEVEL(dB)
30 27 24 21 18 15 12 9 6 4 2
1
-24 -18 -12 -6 0
6 12 18
SMART
0
CH1
4
30
0.5
15
70
0.3
1.5
+4
+10
2
10
6
110
0.1
3
-10
+10
1
1
150
5
0.05
-20
+20
0
SC FILTER
N:1
dB/mSec
MANUAL
dB/Sec
I/O METER
dB
BYPASS
AUTO
COMP
RATIO
ATTACK
RELEASE
OUTPUT GAIN
THRESHOLD
COMPRESSOR
LIMITER
Pic. 1 Front anel of he ACL2 PRO
Pic. 2 Controls of Expander /Gate section
THRESHOLD
LIM
0
SC EXTERANL
SMART
+12
-35
-10
2.5
1.5
+18
-60
7
-30
+10
2
0
1.2
8
OFF
OFF
+15
-40
+20
DUAL MONO
dBu
dBu
1:N
SC MONITOR
dBu
SC FILTER
CH 1 MASTER
THRESHOLD
RATIO
THRESHOLD
COUPLE
EXPANDER / GATE
3 1
P
T
4
-35
2.5
1.5
-60
7
0
1.2
8
OFF
+15
dBu
1:N
THRESHOLD
RATIO
EXPANDER / GATE
2
3
6
GAIN REDUCTION(dB)
INPUT / OUTPUT LEVEL(dB)
30 27 24 21 18 15 12 9 6 4 2
1
-24 -18 -12 -6 0
6 12
18
LIM
0
+12
CH2
4
30
0.5
15
70
0.3
1.5
+4
10
6
110
0.1
3
-10
+10
1
1
150
5
0.05
+20
0
OFF
N:1
dB/mSec
MANUAL
dB/Sec
I/O METER
dB
BYPASS
dBu
AUTO
COMP
RATIO
ATTACK
RELEASE
OUTPUT GAIN
THRESHOLD
COMPRESSOR
LIMITER
ACL2 PRO
ON
+18
COMPRESSOR/
OFF
LIMITER/GATE
POWER
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