SSM-2120 Analog, SSM-2120 Datasheet - Page 5

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

REV. C
DYNAMIC ATTACK AND DECAY RATES
Figure 5 shows the output levels overlayed using a storage
scope. The attack rate is determined by the step size and the
value of C
step size increase. Table I shows the values of total settling
times to within 5 dB, 3 dB, 2 dB and 1 dB of final value with
C
settling time for larger steps is negligible. To calculate the attack
time to final value for any value of C
value in the chart by C
AV
= 10 F. When step sizes exceed 40 dB, the increase in
MONO
OR R
MONO – R
STEREO – R
L
AV
Figure 5. Overlayed Detector Output
. The attack time to final value is a function of the
R
R
100
100
0%
0%
IN
IN
90
10
90
10
IN
IN
= 10k
Figure 4. Detector Output
= 20k
2V
2V
REC
Figure 6. Noise Gate/Downward Expander Control Circuit and Typical Response
AV
/10 F.
R
IN
LL
2V
a. Control Circuit
AV
|I
C
, simply multiply the
AV
IN
|
50ms
LOG AV
1s
V+
V–
1.5M
THRESHOLD
1k
CONTROL
R
T
V
T
39k
V–
CON
–5–
V–
OUT
The decay rates are linear ramps that are dependent on the
current out of the LOG AV pin (set by R
C
the formula:
Decrementation Rate (in dB/s) =
10 dB Step
20 dB Step
30 dB Step
40 dB Step
50 dB Step
60 dB Step
APPLICATIONS
The following applications for the SSM2120 use both the VCAs
and level detectors in conjunction to assimilate a variety of
functions.
The first section describes the arrangement of the threshold
control in each control circuit configuration. These control
circuits form the foundation for the applications to follow which
include the downward expander, compressor/limiter and
compandor.
THRESHOLD CONTROL
Figure 6a shows the control circuit for a typical downward
expander while Figure 6b shows a typical control curve. Here,
the threshold potentiometer adjusts V
unipolar control output. This is typically used in noise gate,
downward expander, and dynamic filter applications. This
potentiometer is used in all applications to control the signal
level versus control voltage characteristics.
Table I. Settling Time (t
AV
R
CON
. The integration or decay time of the circuit is derived from
200
TO +V
5 dB
11.28 ms
16.65
18.15
18.61
C
b. Typical Downward Expander
Control Curve
S
+
) for C
–
3 dB
26.83
28.33
27.79
21.46
SSM2120/SSM2122
THRESHOLD
*
AV
I
= 10 F. t
REF
*LOWER LIMIT CAN BE FIXED
BY CONNECTING A RESISTOR
R
LL
C
T
FROM REC
AV
to provide a negative
V
REF
IN
333
2 dB
30.19
35.56
37.06
37.52
(+144 s)
(+46 s)
– dB
) and the value of
S
= t
IN
S
TO GROUND
(C
AV
= 10 F)
1 dB
46.09
51.46
52.96
53.42