SSM2120/SSM2122

REV. C

–6–

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

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 shown in Figure 8a, with its response in Figure 8b. The value

control amplifier.

STEREO COMPRESSOR/LIMITER

The two control circuits of Figures 6 and 7 can be used in

conjunction to produce composite control voltages. Figures 9a

and 9b show this type of circuit and transfer function for a

stereo compressor/limiter which also acts as a downward

expander for noise gating. The output noise in the absence of a

*

EXPANSION

THRESHOLD

COMPRESSION

THRESHOLD

200

Ω

MONO

OR R

L

FIGURE 6

200

Ω

FIGURE 7

THRESHOLD EXP.

THRESHOLD COM.

a. Control Circuit

b. Input/Output Curve

Figure 9. Control Circuit for Stereo Compressor/Limiter with Noise Gating and Input/Output Curve

+

–

*UPPER LIMIT CAN BE FIXED BY

CONNECTED TO POSITIVE SUPPLY

THRESHOLD

*

2V

V+

V+

CON

OUT

REC IN

39k

Ω

200

Ω

MONO

OR R

THRESHOLD

CONTROL

LOG AV

L

V–

1.5M

Ω

1k

Ω

V–

THRESH

a. Control Circuit

b. Typical Compressor/Limiter Control

Curve

Figure 7. Compressor/Limiter Control Circuit and Typical Response

*UPPER AND

LOWER LIMITS CAN

BE ESTABLISHED BY

+

–

*

*

2V

V+

V+

39k

Ω

200

Ω

MONO

OR R

GAIN

LOG AV

L

V–

1.5M

Ω

1k

Ω

V–

THRESH

V–

a. Control Circuit

b. Typical Compandor Control Curves

Figure 8. Compandor Control Circuit and Typical Curves