Analog Devices SSM2000 Datasheet

HUSH Stereo Noise Reduction System

13

16

15

14

19

18

17

24

23

22

21

20

12

11

10

9

8

1

2

3

4

7

6

5

L IN

R VCF CAP 2

R VCF CAP 1

R OUT

L OUT

R IN

L VCF CAP 1

L VCF CAP 2

DO NOT CONNECT

1

DIGITAL GND

V–

V+

ANALOG COMMON (V+/2)

VCA CONTROL PORT

VCF DET IN

SUM OUT

VCA DET IN

AUTO
THRESHOLD CAP

DEFEAT

MUTE

VCF DET TC

VCA DET TC

DEFAULT
THRESHOLD

2

1kΩ

2nF

500Ω

20nF

3µF

20nF

1.0µF

3.3µF

6.8µF

6.8µF

1nF

0.22µF

DO NOT CONNECT

1

NOTES:

1

MAKE NO CONNECTION TO PINS 13 AND 18

2

DEFAULT THRESHOLD. NORMALLY CONNECTED TO ANALOG COMMON

1nF

SSM2000

a

FEATURES
Up to 25 dB of Noise Reduction from Virtually Any

Audio Source without Sonic Artifacts

“Single-Ended” Operation Eliminates Need for Encode-

Decode Process

Adaptive Threshold Dynamically Adjusts to Changing

Nominal Signal Levels
Effectively Decodes Dolby B
Direct VCA Control Port Access for Additional Level

Control Functionality
Logic-Controllable Bypass and Muting
100 dB Dynamic Range (Noise Reduction OFF)

0.02% Typical THD+N (@ 1 kHz, Noise Reduction OFF)
+7 V to +18 V Operation
No Royalty Requirements

APPLICATIONS
Auto Radio Sound Processing
Multimedia PC Sound Cards
Television Sound Processing
Cassette Tape Players
AM/FM Receivers
Telephone & Wireless Links
Professional Audio

®

Encoded Sources

with Adaptive Threshold

SSM2000

PIN CONFIGURATION

24-Lead Plastic DIP

24-Lead SOIC

1

L IN

R IN
L VCF C1
L VCF C2

V+

ACOM

VCA PORT

VCF DET IN

SUM OUT

VCA DET IN
VCF DET CAP
VCA DET CAP

2
3
4
5

SSM2000

6

TOP VIEW

(Not to Scale)

7
8

9
10
11
12

NC = NO CONNECT

24

L OUT

23

R OUT

22

R VCF C1
R VCF C2

21
20

V–

19

DIGITAL GND
NC

18
17

MUTE
DEFEAT

16

AUTO THRESHOLD CAP

15

DEFAULT THRESHOLD

14
13

NC

GENERAL DESCRIPTION

The SSM2000 is an advanced audio noise reduction system
based on proprietary HUSH

®

circuitry. HUSH combines a dy­namic filter and downward expander to provide a high level of
effectiveness without the sonic artifacts normally associated with
noise reduction systems. In addition, an Adaptive Threshold
circuit detects nominal signal levels and dynamically adjusts
both thresholds, thereby providing optimal results regardless of
program source. Since it is a single-ended system, HUSH can
be used on virtually any audio source, including audio and
video tapes, radio and television broadcasts, or any other source
with objectionable noise. The SSM2000 can be used with
Dolby B
direct access to the Voltage Controlled Amplifier port enabling
additional functions such as dc volume control, automatic level­ing, compression, etc. with minimal external circuitry.

Dolby B is a registered trademark of Dolby Laboratories, Inc.
HUSH is a registered trademark of Rocktron Corporation.

REV. 0

Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices. (See page 16.)

encoded sources with excellent results. A key feature is

Figure 1. Typical Basic Application

© Analog Devices, Inc., 1996

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] Fax: [phone]

SSM2000–SPECIFICATIONS

MASKED NOISE FILTERED NOISE

AUDIO

SIGNAL

6 dB/OCTAVE SLOPE

f

C

= 3 kHz TO 37 kHz

PASSBAND FREQUENCY

RESPONSE ±0.5 dB

(VS = +8.5 V, ACOM = VS/2, f = 1 kHz, RL = 100 kV, 0 dBu = 0.775 V rms.

TA = +258C, Noise Reduction and Adaptive Threshold enabled (Pin 14 at VS/2), unless otherwise noted.)

SSM2000

Parameter Symbol Conditions Min Typ Max Units

AUDIO SIGNAL PATH

Signal-to-Noise Ratio SNR V

= 0 V, 20 Hz to 20 kHz (Flat) 80 86 dB

IN

Headroom HR Clip Point, THD = 1% 4.5 dBu
Dynamic Range Clipping to Noise Floor 91 dB
Total Harmonic Distortion THD+N V

= 300 mV rms, 2nd & 3rd Harmonics

IN

1

0.02 0.04 %

Effective Noise Reduction 20 kHz Bandwidth (Flat)

Downward Expander Section 15 dB

Dynamic Filter Section 10 dB
Input Impedance Z
Output Impedance, Dynamic Z

IN
OUT

Pins 1 and 2 6 8 kΩ

Pins 23 and 24 7 Ω
Capacitive Load No Oscillation 300 pF
Channel Separation f = 1 kHz, V
Mute Output V

= 300 mV rms –85 dB

IN

Gain Matching, L & R Channels VCA at A

= 300 mV rms 60 dB

IN

= 0 dB ±1dB

V

Gain Bandwidth GBW NR Disabled 37 kHz

DYNAMIC FILTER

Minimum Bandwidth BW
Maximum Bandwidth BW

MIN
MAX

VCF C = 0.001 µF 3 kHz

37 kHz

VCA CONTROL PORT

Input Impedance Pin 7 3.8 kΩ
VCA Voltage Gain Range A

V

VIN = 300 mV rms (Pin 7 = 2.0 V & 0 V) –70 +1 dB
Gain Constant 20 22 26 mV/dB
Control Feedthrough Pin 7 1 10 mV

POWER SUPPLY

Voltage Range V
Supply Current I

S

SY

+7.0 18 V

7.5 11 mA

Power Supply Rejection PSRR+ 70 dB

VCA, VCF DETECTOR

Input Impedance R

NOTES

1

NR in defeat mode.

Specifications subject to change without notice.

0
–10
–20
–30
–40

INPUT

–50

LEVEL

–60
–70
–80
–90

Figure 2. Downward Expander Attenuation Characteristic

–100

IN

(In dBt; 0 dBt = Threshold)

Pins 8 and 10 4.0 5.4 7.0 kΩ

0
–10
–20
–30
–40

OUTPUT

–50

LEVEL

–60
–70
–80
–90
–100

Figure 3. Dynamic Filter Characteristic (For CF = 0.001 µF
Defeat Mode)

–2–

REV. 0

PIN DESCRIPTION

WARNING!

ESD SENSITIVE DEVICE

SSM2000

Pin # Name Function and Explanation

1 L IN Left Audio Input.
2 R IN Right Audio Input.
3 L VCF C1 Left VCF Filter Cap Port.
4 L VCF C2 Left VCF Filter Cap Port.
5 V+ Positive Supply.
6 ACOM Analog Common Voltage. In-

ternal Circuit Ground Point.
Must be held to a voltage ap­proximately halfway between
V+ and V–. Should be a clean
low impedance voltage source
capable of at least 4 mA, such
as from a buffer driven off a
supply-splitting voltage divider.

7 VCA PORT Input to VCA Control Port.

Allows external adjustment of
attenuation with a +22 mV/dB
slope. Zero volts relative to
ACOM gives zero additional
attenuation. Should be con­nected to ACOM if function

not required.
8 VCF DET IN Input to VCF Detector.
9 SUM OUT Combined Left Plus Right

Output.
10 VCA DET IN Input to VCA Detector.
11 VCF DET CAP Voltage Controlled Filter.

Time Constant Capacitor Port.
12 VCA DET CAP Voltage Controlled Amplifier.

Time Constant Capacitor Port.

Pin # Name Function and Explanation

13 NC Make No Connection to this

Pin.

14 DEFAULT Default Threshold Adjust-

THRESHOLD ment Port. Allows reduction

of noise reduction action if
signal source is relatively
clean such as CD sources.
Normally connected to Analog
Common. –1.2 V is recom­mended for CDs; –2 V com­pletely defeats noise reduction.

15 AUTO THRESHOLD

CAP Automatic Threshold Detec-

tor Capacitor Port.

16 DEFEAT Logic High: Defeats Noise

Reduction.
Logic Low: Normal Action.
Connect to Ground if not used.

17 MUTE Logic High: Mute.

Logic Low: Normal Action.
Connect to Ground if not used.

18 NC Make no connection to this

pin.

19 DIGITAL GND Digital Logic Reference

(Logic Zero).
20 V– Negative Supply.
21 R VCF C2 Right VCF Capacitor Port.
22 R VCF C1 Right VCF Capacitor Port.
23 R OUT Right Audio Output.
24 L OUT Left Audio Output.

ABSOLUTE MAXIMUM RATINGS

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +18 V

Audio Input Voltage . . . . . . . . . . . . . . . . . . Supply Voltage(s)

Control Port Voltage (Pin 7) . . . . . . . . . . . . . . Positive Supply

Default Override (Pin 14) . . . . . . . . . . . . . . . . . . . . . . . . . V+

Defeat (Pin 16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V+

Mute Override (Pin 17) . . . . . . . . . . . . . . . . . . . . . . . . . . . V+

Operating Temperature Range . . . . . . . . . . . . –40°C to +85°C

Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C

Junction Temperature (T

Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . . +300°C

ESD RATINGS

883 (Human Body) Model . . . . . . . . . . . . . . . . . . . . . . 2.5 kV

EIAJ Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 V

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the SSM2000 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.

REV. 0

) . . . . . . . . . . . . . . . . . . . . . +150°C

J

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

SSM2000P –40°C to +85°C 24-Pin Plastic DIP N-24
SSM2000S –40°C to +85°C 24-Pin SOIC SOL-24

PACKAGE INFORMATION

Package Type u

1

JA

u

JC

24-Pin Plastic DIP (P) 54 27 °C/W
24-Pin SOIC (S) 72 24 °C/W

NOTE

1

θJA is specified for the worst case conditions, i.e., θJA is specified for device in socket

for P-DIP packages; θJA is specified for device soldered onto a circuit board for
surface mount packages..

–3–

Units

SSM2000

DEFEAT

EXTERNAL VCA
CONTROL PORT

R

OUT

L

OUT

R

IN

L

IN

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

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

C1

JA1

RCA

LEFT IN

JA2

RCA

RIGHT IN

THRESHOLD

20kΩ

Figure 4. Typical Dual Supply Application and Test Circuit

6.8µF

6.8µF

SW1-F

SIDE CHAIN
OPEN = OUT

CLOSED = IN

R1

C5

1kΩ

0.022µF

R2

C6

510Ω

0.022µF
10%

+5V

LEVEL

R7, 10kΩ

PT10V

–5V

R11

12kΩ

14

U1-D

OP482

R12

9

10

C2

0.001µF

C4

0.0022µF

3.3µF

SW1-A

OPEN = COMP
CLOSED = LEVEL

R8

20kΩ

13

12

R13

20kΩ

8

U1-C

OP482

1

2

3

C3

4

5

+5V

6

7

8

9

C7

2.2µF
10

C8
1µF

11

12

C9

R10

5.1kΩ

C12
1µF NON-POLARIZED
10% POLY, 63V

R17

20kΩ

SSM2000

R9

7.5kΩ

SW1-D

OPEN = LEVEL
CLOSED = COMP

24

23

22

21

20

19

18

17

16

15

14

13

R14

100kΩ

R16

1.5MΩ

–5V

NC

C11

0.22µF

NC

C10

0.001µF

+5V

+5V

3

2

1N4148

SW1-E

OPEN = LEVEL
CLOSED = COMP

R18

30kΩ

R19

20kΩ

D2

1N4148

6

5

U1-B

OP482

R3
3kΩ

R4
3kΩ

U1-A

OP482

7

1

JA3
RCA
LEFT OUT

JA4
RCA
RIGHT OUT

SW1-C

MUTE
OPEN = MUTE
CLOSED = OFF

SW1-B

BYPASS
OPEN = BYPASS
CLOSED = HUSH

R15

10MΩ

–5V

VOLUME
CONTROL

VR1, 10kΩ
LINEAR

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 au­dio signals are passed through voltage controlled (low-pass) fil­ter, 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 sig­nals are derived and applied to both the VCF and VCA, result­ing in up to 25 dB noise suppression with the minimum loss of
desired signals.

–5V

Figure 5. SSM2000 System Block Diagram

–4–

REV. 0

T ypical Performance Characteristics–SSM2000

10

TA = +25°C
VS = ± 4.25V (Pin 5, 20)
DEF THRESHOLD = 0V (Pin 14)

DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)

1

= 100kΩ

R

L

BOTH CHANNELS

THD + N – %

0.1

0.01

0.01 20.1
INPUT SIGNAL – V

rms

Figure 6. THD+N (%) vs. Input Signal

1

TA = +25°C
V

= ± 4.25V (Pin 5, 20)

S

= 300mV

rms

V

IN

DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)

0.1

MUTE = OFF (Pin 17)

= 100kΩ

R

L

BOTH CHANNELS

THD + N – %

0.01

0.001
20 30k100

SINE WAVE (Pin 1, 2)

1k 10k

FREQUENCY – Hz

0

–10

–20

–30

–40

V

TH

V

–70 0–60

= –2.0V

V

TH

= 0V

TH

–50 –40 –30 –20 –10

TA = +25°C
VS = ± 4.25V (Pin 5, 20)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)

= –1.2V

MUTE = OFF (Pin 17)

= 100kΩ

R

L

0dBu = 0.775mV

INPUT SIGNAL – dBu

@ 1kHz

rms

–50

–60

–70

OUTPUT SIGNAL – dBu

–80

–90

1

–100

Figure 9. Output vs. Input Characteristics (With Different
Adaptive Threshold Voltage, Pin 17)

10

0

–10

–20

–30

–40

TA = +25°C
V

= ± 4.25V (Pin 5, 20)

S

–50

= 300mV

rms

V

IN

–60

DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)

L, R CHANNEL OUTPUT – dB

–70

MUTE = OFF (Pin 17)

= 100kΩ

R

L

–80

BOTH CHANNELS

–90

–1 3–0.5

SINE WAVE (Pin 1, 2)

0 0.5 1 1.5 2 2.5

VCA CONTROL VOLTAGE (Pin 7) – V

REV. 0

Figure 7. THD+N (%) vs. Frequency

6

4

2

0

–2

TA = +25°C
VS = ± 4.25V (Pin 5, 20)

–4

GAIN – dB

–6

–8

–10

–12

= 300mV

rms

V

IN

DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)

= 100kΩ

R

L

BOTH CHANNELS

20 200k100

SINE WAVE (Pin 1, 2)

1k 10k 100k

FREQUENCY – Hz

Figure 8. –3 dB Bandwidth

Figure 10a. Channel Output vs. VCA Control Voltage (Pin 7)

3.00

0.7

–1.6

–3.9

–6.2

–8.5

TA = +25°C

–10.8

V

GAIN – dB

–13.1

–15.4

–17.7
–20.0

= ± 4.25V (Pin 5, 20)

S

= 300mVrms SINE WAVE (Pin 1, 2)

V

IN

DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)
MUTE = OFF (Pin 17)

R

= 100kΩ

L

20 80k100

40kHz

20kHz

8kHz

6kHz

4kHz

100 – 2kHz MIN BW

1k 10k

FREQUENCY – Hz

50kHz

Figure 10b. VFC Characteristics (Simulated Noise Level
90 mV rms with Different Frequency) Applied through a
3-Pole HP filter

–5–