6

5/90, Rev. B1

SSM-2120/SSM-2122 DYNAMIC RANGE PROCESSOR/DUAL VCA

b)

a) CONTROL CIRCUIT

FIGURE 6:

Noise Gate/Downward Expander Control Circuit and Typical Response.

FIGURE 7:

Compressor/Limiter Control Circuit and Typical Response.

lar 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.

In the noise gate, downward expander and compressor/limiter

applications, this potentiometer will establish the onset of the

control action. The sensitivity of the control action depends on

the value of R

T

.

For a positive unipolar control output add two diodes as shown

in Figure 7a. This is useful in compressor/limiter applications.

Figure 7b shows a typical response.

Bipolar control outputs can be realized by adding a resistor from

the op amp output to V+. This is useful in compandor circuits as

APPLICATIONS

The following applications for the SSM-2120 use both the VCAs

and level detectors in conjunction to assimilate a variety of func-

tions.

The first section describes the arrangement of the threshold

control in each control circuit configuration. These control cir-

cuits form the foundation for the applications to follow which in-

clude the downward expander, compressor/limiter and compan-

dor.

THRESHOLD CONTROL

Figure 6a shows the control circuit for a typical downward ex-

pander while Figure 6b shows a typical control curve. Here, the

threshold potentiometer adjusts V

T

to provide a negative unipo-

b)

a) CONTROL CIRCUIT

TYPICAL DOWNWARD EXPANDER

CONTROL CURVE

+

–

*

THRESHOLD

+

–

200

Ω

CON

OUT

1k

Ω

THRESH

THRESHOLD

CONTROL

V+

LOG AV

MONO

OR R

+

2V

+

–

REC IN

+

L

1.5M

Ω

V–

39k

Ω

V+

V–

TYPICAL COMPRESSOR/LIMITER

CONTROL CURVE

*

THRESHOLD

+

–

+

–

200

Ω

CON

OUT

39k

Ω

THRESHOLD CONTROL

V–

V+

LOG AV

MONO

OR R

+

2V

+

–

REC

IN

+

L

1.5M

Ω

V–

1k

Ω

V–

OBSOLETE