SSM2000.PDF

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a
HUSH Stereo Noise Reduction System
with Adaptive Threshold
SSM2000
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 ® Encoded Sources
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
PIN CONFIGURATION
24-Lead Plastic DIP
24-Lead SOIC
L IN
1
2
3
4
24
23
22
21
20
19
18
17
L OUT
R IN
L VCF C1
L VCF C2
R OUT
R VCF C1
R VCF C2
V+
ACOM
VCA PORT
VCF DET IN
SUM OUT
VCA DET IN
5
SSM2000
V–
6
TOP VIEW
(Not to Scale)
DIGITAL GND
7
NC
8
MUTE
9
16
15
14
DEFEAT
10
AUTO THRESHOLD CAP
VCF DET CAP
VCA DET CAP
11
DEFAULT THRESHOLD
NC
APPLICATIONS
Auto Radio Sound Processing
Multimedia PC Sound Cards
Television Sound Processing
Cassette Tape Players
AM/FM Receivers
Telephone & Wireless Links
Professional Audio
12
13
NC = NO CONNECT
6.8µF
L IN
1
24
L OUT
6.8µF
GENERAL DESCRIPTION
The SSM2000 is an advanced audio noise reduction system
based on proprietary HUSH ® circuitry. HUSH combines a dy-
namic 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 encoded sources with excellent results. A key feature is
direct access to the Voltage Controlled Amplifier port enabling
additional functions such as dc volume control, automatic level-
ing, compression, etc. with minimal external circuitry.
Dolby B is a registered trademark of Dolby Laboratories, Inc.
HUSH is a registered trademark of Rocktron Corporation.
R IN
2
23
R OUT
L VCF CAP 1
3
22
R VCF CAP 1
1nF
1nF
L VCF CAP 2
4
21
R VCF CAP 2
V+
5
20
V–
SSM2000
ANALOG COMMON (V+/2)
6
19
DIGITAL GND
VCA CONTROL PORT
7
18
DO NOT CONNECT 1
20nF
2nF
VCF DET IN
8
17
MUTE
20nF
500
W
1k
W
9
16
DEFEAT
SUM OUT
VCA DET IN
3µF
0.22µF
AUTO
THRESHOLD CAP
10
15
1.0µF
VCF DET TC
11
14
DEFAULT
THRESHOLD 2
3.3µF
VCA DET TC
12
13
DO NOT CONNECT 1
NOTES:
1 MAKE NO CONNECTION TO PINS 13 AND 18
2 DEFAULT THRESHOLD. NORMALLY CONNECTED TO ANALOG COMMON
Figure 1. Typical Basic Application
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.)
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
376120087.035.png 376120087.036.png 376120087.037.png
 
SSM2000–SPECIFICATIONS
(V S = +8.5 V, ACOM = V S /2, f = 1 kHz, R L = 100 k
V
, 0 dBu = 0.775 V rms.
T A = +25
8
C, Noise Reduction and Adaptive Threshold enabled (Pin 14 at V S /2), unless otherwise noted.)
SSM2000
Parameter
Symbol Conditions
Min
Typ
Max
Units
AUDIO SIGNAL PATH
Signal-to-Noise Ratio
SNR
V IN = 0 V, 20 Hz to 20 kHz (Flat)
80
86
dB
Headroom
HR
Clip Point, THD = 1%
4.5
dBu
Dynamic Range
Clipping to Noise Floor
91
dB
Total Harmonic Distortion
THD+N V IN = 300 mV rms, 2nd & 3rd Harmonics 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 IN
Pins 1 and 2
6
8
kW
Output Impedance, Dynamic
Z OUT
Pins 23 and 24
7
W
Capacitive Load
No Oscillation
300
pF
Channel Separation
f = 1 kHz, V IN = 300 mV rms
60
dB
Mute Output
V IN = 300 mV rms
–85
dB
Gain Matching, L & R Channels
VCA at A V = 0 dB
± 1
dB
Gain Bandwidth
GBW
NR Disabled
37
kHz
DYNAMIC FILTER
Minimum Bandwidth
BW MIN
VCF C = 0.001 mF
3
kHz
Maximum Bandwidth
BW MAX
37
kHz
VCA CONTROL PORT
Input Impedance
Pin 7
3.8
W
VCA Voltage Gain Range
A V
V IN = 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 S
+7.0
18
V
Supply Current
I SY
7.5
11
mA
Power Supply Rejection
PSRR+
70
dB
VCA, VCF DETECTOR
Input Impedance
R IN
Pins 8 and 10
4.0
5.4
7.0
W
NOTES
1 NR in defeat mode.
Specifications subject to change without notice.
PASSBAND FREQUENCY
RESPONSE ± 0.5 dB
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
f C = 3 kHz TO 37 kHz
INPUT
LEVEL
OUTPUT
LEVEL
AUDIO
SIGNAL
6 dB/OCTAVE SLOPE
MASKED NOISE
FILTERED NOISE
Figure 2. Downward Expander Attenuation Characteristic
(In dBt; 0 dBt = Threshold)
Figure 3. Dynamic Filter Characteristic (For C F = 0.001 m F
Defeat Mode)
–2–
REV. 0
k
k
376120087.001.png 376120087.002.png
SSM2000
PIN DESCRIPTION
Pin # Name
Function and Explanation
Pin # Name
Function and Explanation
1
L IN
Left Audio Input.
13
NC
Make No Connection to this
Pin.
2
R IN
Right Audio Input.
3
L VCF C1
Left VCF Filter Cap Port.
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 recom-
mended for CDs; –2 V com-
pletely defeats noise reduction.
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 ap-
proximately 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.
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.
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 con-
nected to ACOM if function
not required.
17
MUTE
Logic High: Mute.
Logic Low: Normal Action.
Connect to Ground if not used.
18
NC
Make no connection to this
pin.
8
VCF DET IN
Input to VCF Detector.
19
DIGITAL GND
Digital Logic Reference
(Logic Zero).
9
SUM OUT
Combined Left Plus Right
Output.
20
V–
Negative Supply.
10
VCA DET IN
Input to VCA Detector.
21
R VCF C2
Right VCF Capacitor Port.
11
VCF DET CAP
Voltage Controlled Filter.
Time Constant Capacitor Port.
22
R VCF C1
Right VCF Capacitor Port.
12
VCA DET CAP
Voltage Controlled Amplifier.
Time Constant 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
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
C to +85
°
C
PACKAGE INFORMATION
Storage Temperature Range . . . . . . . . . . . . –65
°
C to +150
°
C
Junction Temperature (T J ) . . . . . . . . . . . . . . . . . . . . . +150
°
C
Package Type
u
JA 1
u
JC
Units
Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . . +300
°
C
24-Pin Plastic DIP (P)
54
27
°
C/W
ESD RATINGS
883 (Human Body) Model . . . . . . . . . . . . . . . . . . . . . . 2.5 kV
EIAJ Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 V
24-Pin SOIC (S)
72
24
°
C/W
JA is specified for the worst case conditions, i.e.,
q
JA is specified for device in socket
JA is specified for device soldered onto a circuit board for
surface mount packages..
q
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.
WARNING!
ESD SENSITIVE DEVICE
REV. 0
–3–
°
q
NOTE
1
for P-DIP packages;
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SSM2000
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.
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.
JA1
RCA
LEFT IN
JA2
RCA
RIGHT IN
C1
6.8µF
JA3
RCA
LEFT OUT
JA4
RCA
RIGHT OUT
1
24
C2
6.8µF
2
23
3
22
C3
0.001µF
C10
0.001µF
4
21
VOLTAGE
CONTROLLED
FILTER
VOLTAGE
CONTROLLED
AMPLIFIER
SSM2000
R IN
R OUT
+5V
5
20
–5V
SW1-F
SIDE CHAIN
OPEN = OUT
CLOSED = IN
6
19
SW1-C
MUTE
OPEN = MUTE
CLOSED = OFF
+5V
VOLTAGE
CONTROLLED
FILTER
VOLTAGE
CONTROLLED
AMPLIFIER
7
18
NC
L IN
L OUT
R3
3k
C4
0.0022µF
W
8
17
R1
1k
W
C5
0.022µF
9
16
LOGIC
INTERFACE
C7
2.2µF
C11
0.22 µ F
SW1-B
BYPASS
OPEN = BYPASS
CLOSED = HUSH
DEFEAT
EXTERNAL VCA
CONTROL PORT
+5V
R4
3k
10
15
C8
1µF
LOGIC
INTERFACE
R2
510
W
C6
0.022µF
10%
W
MUTE
11
14
DEFAULT
THRESHOLD
12
13
NC
C9
3.3µF
U1-A
OP482
A UTO THRESHOLD
NEGATIVE PEAK
DETECTOR
DIFFERENCE
AMPLIFIER
SW1-A
OPEN = COMP
CLOSED = LEVEL
3
R9
7.5k
1
R16
1.5M
W
W
2
+5V
R8
20k
R10
5.1k
HIGH-PASS
FILTER
PEAK
DETECTOR
LEVEL
THRESHOLD
R7, 10k
W
W
DIFFERENCE
AMPLIFIER
W
PT10V
1N4148
PEAK
DETECTOR
–5V
SW1-D
OPEN = LEVEL
CLOSED = COMP
SW1-E
OPEN = LEVEL
CLOSED = COMP
R11
12k
W
R15
10M
Figure 5. SSM2000 System Block Diagram
–5V
13
14
R14
100k
–5V
W
12
R18
30k
W
VOLUME
CONTROL
VR1, 10k
U1-D
OP482
C12
1µF NON-POLARIZED
10% POLY, 63V
R19
20k
W
R12
20k
W
LINEAR
W
R13
20k
W
D2
1N4148
9
R17
20k
8
W
6
10
7
U1-C
OP482
5
U1-B
OP482
Figure 4. Typical Dual Supply Application and Test Circuit
–4–
REV. 0
W
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Typical Performance Characteristics–SSM2000
10
0
T A = +25 ° C
V S =
4.25V (Pin 5, 20)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
BOTH CHANNELS
–10
–20
1
–30
–40
–50
V TH = –2.0V
–60
T A = +25 ° C
V S = ± 4.25V (Pin 5, 20)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
0dBu = 0.775mV rms
0.1
–70
–80
V TH = –1.2V
–90
V TH = 0V
0.01
0.01
0.1
1
2
–100
–70
–60
–50
–40
–30
–20
–10
0
INPUT SIGNAL – V rms
INPUT SIGNAL – dBu
@ 1kHz
Figure 6. THD+N (%) vs. Input Signal
Figure 9. Output vs. Input Characteristics (With Different
Adaptive Threshold Voltage, Pin 17)
1
10
T A = +25 ° C
V S = ± 4.25V (Pin 5, 20)
V IN = 300mV rms SINE WAVE (Pin 1, 2)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
BOTH CHANNELS
0
0.1
–10
–20
–30
–40
T A = +25 ° C
V S = ± 4.25V (Pin 5, 20)
V IN = 300mV rms SINE WAVE (Pin 1, 2)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
BOTH CHANNELS
–50
0.01
–60
–70
–80
0.001 20
100
1k
10k
30k
–90 –1
–0.5
0
0.5
1
1.5
2
2.5
3
FREQUENCY – Hz
VCA CONTROL VOLTAGE (Pin 7) – V
Figure 7. THD+N (%) vs. Frequency
Figure 10a. Channel Output vs. VCA Control Voltage (Pin 7)
6
3.00
4
0.7
50kHz
2
–1.6
40kHz
–3.9
0
20kHz
–6.2
–2
8kHz
T A = +25 ° C
V S =
–8.5
–4
4.25V (Pin 5, 20)
V IN = 300mV rms SINE WAVE (Pin 1, 2)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
BOTH CHANNELS
T A = +25 ° C
V S =
–10.8
4.25V (Pin 5, 20)
V IN = 300mV rms SINE WAVE (Pin 1, 2)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = OFF (Pin 16)
MUTE = OFF (Pin 17)
R L = 100k W
–6
–13.1
6kHz
–8
–15.4
–17.7
4kHz
–10
100 – 2kHz MIN BW
–12 20
100
1k
10k
100k
200k
–20.0
20
100
1k
10k
80k
FREQUENCY – Hz
FREQUENCY – Hz
Figure 8. –3 dB Bandwidth
Figure 10b. VFC Characteristics (Simulated Noise Level
90 mV rms with Different Frequency) Applied through a
3-Pole HP filter
REV. 0
–5–
±
±
±
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