7

5/90, Rev. B1

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

FIGURE 8:

Compandor Control Circuit and Typical Curves.

b)

b)

a) CONTROL CIRCUIT

FIGURE 9:

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

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

the resistor R

PV

will determine the maximum output from the

control amplifier.

STEREO COMPRESSOR/LIMITER

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

junction 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 signal will be

dependent on the noise of the current-to-voltage converter am-

plifier if the expansion ratio is high enough.

As discussed in the Threshold Control section, the use of the con-

trol circuit of Figure 5, including the R

PV

to V+ and two diodes,

yields positive unipolar control outputs.

a) CONTROL CIRCUIT

EXPANSION

THRESHOLD

INPUT/OUTPUT CURVE

COMPRESSION

THRESHOLD

FIGURE 6

THRESHOLD EXP.

FIGURE 7

THRESHOLD COM.

200

Ω

200

Ω

MONO

OR R

L

+V

C

–V

C

+

–

200

Ω

CON

OUT

1k

Ω

THRESH

GAIN

V+

LOG AV

MONO

OR R

+

2V

+

–

REC

IN

+

L

1.5M

Ω

V–

39k

Ω

V+

V–

V–

TYPICAL COMPANDOR

CONTROL CURVES

*

*

+

–

OBSOLETE