SSM-2120 Analog, SSM-2120 Datasheet - Page 8

• Manufacturer Part Number: SSM-2120
• Description: (SSM-2122) Dynamic Range Processors/Dual VCA
• Manufacturer: Analog

SSM2120/SSM2122
DYNAMIC FILTER
Figure 12 shows a control circuit for a dynamic filter capable of
single ended (nonencode/decode) noise reduction. Such circuits
usually suffer from a loss of high frequency content at low signal
levels because their control circuits detect the absolute amount
of highs present in the signal. This circuit, however, measures
wideband level as well as high frequency band level to produce
a composite control signal combined in a 1:2 ratio respectively.
The upper detector senses wideband signals with a cutoff of
20 Hz while the lower detector has a 5 kHz cutoff to sense only
high frequency band signals. This approach allows very good
noise masking with a minimum loss of “highs” when the signal
level goes below the threshold.
AUDIO
INPUT
10k
10k
(HIGH FREQUENCY)
(WIDEBAND)
F
F
C
C
3300pF
2.2µF
= 5kHz
20Hz
REC
REC
15
9
IN
IN
3.3µF
3.3µF
|I
|I
IN
IN
|
|
V+
V–
V+
V–
LOG AV
LOG AV
13
2
1.5M
1.5M
THRESHOLD
CONTROL
Figure 12. Dynamic Noise Filter Circuit
160k
160k
1k
1k
V–
THRESH
THRESH
12
1
39k
39k
36k
–8–
CON
CON
V–
V–
OUT
OUT
14
3
2200pF
47
12k
5.6k
200
8
SIG
IN
7
5
+V
–V
200
C
C
SIG
36k
OUT
5
36k
36k
100pF
AUDIO
OUTPUT
REV. C