SSM2000 Analog, SSM2000 Datasheet - Page 4

• Manufacturer Part Number: SSM2000
• Description: HUSH Stereo Noise Reduction System with Adaptive Threshold
• Manufacturer: Analog

SSM2000
APPLICATIONS
This applications example (Figure 4) demonstrates some of the
additional functions that can be easily implemented through use
of the VCA Control Port (Pin 7). These functions can be selected
to operate simultaneously with the basic HUSH noise reduction
function. The VCA detector output provides a signal which can
be further processed using one quad op amp (OP482) to provide
these various additional useful functions.
The circuit shown in the figure below achieves: (1) Compres-
sion, (2) Volume Leveling, (3) DC Volume Adjustment.
Figure 4. Typical Dual Supply Application and Test Circuit
RIGHT IN
LEFT IN
THRESHOLD
RCA
RCA
20k
JA1
JA2
R12
510
1k
R1
R2
R7, 10k
CLOSED = IN
OPEN = OUT
LEVEL
SIDE CHAIN
PT10V
SW1-F
9
10
14
OP482
U1-D
0.022µF
C5
0.022µF
–5V
+5V
12k
10%
R11
C6
6.8µF
6.8µF
20k
C1
C2
R13
OP482
U1-C
20k
0.001µF
R8
C4
0.0022µF
OPEN = COMP
CLOSED = LEVEL
13
12
8
3.3µF
C9
+5V
C3
C7
2.2µF
SW1-A
C8
1µF
C12
1µF NON-POLARIZED
10% POLY, 63V
10
11
12
1
2
3
4
5
6
7
8
9
20k
R17
5.1k
R10
SSM2000
OPEN = LEVEL
CLOSED = COMP
7.5k
R9
SW1-D
100k
24
23
22
21
20
19
18
17
16
15
14
13
R14
1.5M
R16
–5V
NC
C11
0.22µF
NC
C10
0.001µF
6
5
20k
R19
OPEN = LEVEL
CLOSED = COMP
3
2
1N4148
OP482
1N4148
U1-B
30k
SW1-E
D2
+5V
+5V
R18
OP482
U1-A
R4
3k
7
R3
3k
1
BYPASS
OPEN = BYPASS
CLOSED = HUSH
MUTE
OPEN = MUTE
CLOSED = OFF
–5V
JA3
RCA
LEFT OUT
JA4
RCA
RIGHT OUT
SW1-C
SW1-B
VOLUME
CONTROL
VR1, 10k
LINEAR
10M
R15
–5V
–4–
SIMPLIFIED THEORY OF OPERATION
The input audio signals are processed to extract information
concerning the frequency distribution and amplitude of both
the desired signals and the undesired noise. Left and right au-
dio signals are passed through voltage controlled (low-pass) fil-
ter, and then through a voltage controlled amplifiers. Both the
filters and amplifiers are low distortion, and add negligible noise
of their own. The VCF has a user-definable cutoff range that is
usually set from 1 kHz to 35 kHz. It can be set to cover other
ranges as required by the application. The VCA can be adjusted
from a loss to a gain, adding to the SSM2000’s versatility. In
accordance with proprietary patented algorithms, control sig-
nals are derived and applied to both the VCF and VCA, result-
ing in up to 25 dB noise suppression with the minimum loss of
desired signals.
R
L
IN
IN
Figure 5. SSM2000 System Block Diagram
DEFEAT
MUTE
CONTROLLED
CONTROLLED
VOLTAGE
VOLTAGE
FILTER
FILTER
HIGH-PASS
FILTER
INTERFACE
INTERFACE
LOGIC
LOGIC
DETECTOR
DETECTOR
AUTO THRESHOLD
NEGATIVE PEAK
PEAK
PEAK
THRESHOLD
DETECTOR
DEFAULT
CONTROLLED
CONTROLLED
AMPLIFIER
AMPLIFIER
VOLTAGE
VOLTAGE
CONTROL PORT
EXTERNAL VCA
DIFFERENCE
DIFFERENCE
AMPLIFIER
AMPLIFIER
REV. 0
R
L
OUT
OUT