SSM2000

REV. 0

–4–

APPLICATIONS

This applications example (Figure 4) demonstrates some of the

additional functions that can be easily implemented through use

of the VCA Control Port (Pin 7). These functions can be selected

to operate simultaneously with the basic HUSH noise reduction

function. The VCA detector output provides a signal which can

be further processed using one quad op amp (OP482) to provide

these various additional useful functions.

The circuit shown in the figure below achieves: (1) Compres-

sion, (2) Volume Leveling, (3) DC Volume Adjustment.

C3

0.001µF

C10

0.001µF

NC

C2

6.8µF

+5V

–5V

C1

6.8µF

C4

0.0022µF

12

11

10

9

8

1

2

3

4

7

6

5

13

16

15

14

19

18

17

24

23

22

21

20

SSM2000

C7

2.2µF

C6

0.022µF

10%

JA1

RCA

LEFT IN

JA2

RCA

RIGHT IN

C5

0.022µF

R1

1k

Ω

NC

C8

1µF

C9

3.3µF

R2

510

Ω

+5V

R3

3k

Ω

SW1-C

MUTE

OPEN = MUTE

CLOSED = OFF

C11

0.22µF

+5V

R4

3k

Ω

SW1-B

BYPASS

OPEN = BYPASS

CLOSED = HUSH

SW1-F

SIDE CHAIN

OPEN = OUT

CLOSED = IN

JA3

RCA

LEFT OUT

JA4

RCA

RIGHT OUT

R16

1.5M

Ω

U1-A

OP482

3

2

1

1N4148

SW1-E

OPEN = LEVEL

CLOSED = COMP

R15

10M

Ω

SW1-A

OPEN = COMP

CLOSED = LEVEL

R9

7.5k

Ω

R10

5.1k

Ω

R8

20k

Ω

+5V

–5V

LEVEL

THRESHOLD

R7, 10k

Ω

PT10V

U1-D

OP482

13

12

14

R11

12k

Ω

SW1-D

OPEN = LEVEL

CLOSED = COMP

R14

100k

Ω

–5V

C12

1µF NON-POLARIZED

10% POLY, 63V

R12

20k

Ω

9

10

8

R13

20k

Ω

U1-C

OP482

R17

20k

Ω

U1-B

OP482

6

5

7

D2

1N4148

R19

20k

Ω

–5V

VOLUME

CONTROL

VR1, 10k

Ω

LINEAR

R18

30k

Ω

Figure 4. Typical Dual Supply Application and Test Circuit

SIMPLIFIED THEORY OF OPERATION

The input audio signals are processed to extract information

concerning the frequency distribution and amplitude of both

the desired signals and the undesired noise. Left and right au-

dio signals are passed through voltage controlled (low-pass) fil-

ter, and then through a voltage controlled amplifiers. Both the

filters and amplifiers are low distortion, and add negligible noise

of their own. The VCF has a user-definable cutoff range that is

usually set from 1 kHz to 35 kHz. It can be set to cover other

ranges as required by the application. The VCA can be adjusted

from a loss to a gain, adding to the SSM2000’s versatility. In

accordance with proprietary patented algorithms, control sig-

nals are derived and applied to both the VCF and VCA, result-

ing in up to 25 dB noise suppression with the minimum loss of

desired signals.

DEFEAT

EXTERNAL VCA

CONTROL PORT

DEFAULT

THRESHOLD

VOLTAGE

CONTROLLED

FILTER

VOLTAGE

CONTROLLED

AMPLIFIER

LOGIC

INTERFACE

VOLTAGE

CONTROLLED

FILTER

VOLTAGE

CONTROLLED

AMPLIFIER

MUTE

LOGIC

INTERFACE

DIFFERENCE

AMPLIFIER

AUTO THRESHOLD

NEGATIVE PEAK

DETECTOR

HIGH-PASS

FILTER

PEAK

DETECTOR

PEAK

DETECTOR

DIFFERENCE

AMPLIFIER

Figure 5. SSM2000 System Block Diagram