SSM2000P Fast Delivery |IC PHOENIX CO.,LIMITED

SSM2000P ,HUSH Stereo Noise Reduction System with Adaptive ThresholdSpecifications subject to change without notice.PASSBAND FREQUENCYRESPONSE ±0.5 dB00f = 3 kHz TO 37 ..
SSM2005 ,Decoder 5.1-Channel Soundfield Generatorspecifications or is not in the consumer electronics classification.All equipment manufactured usin ..
SSM2005RS-REEL ,Decoder 5.1-Channel Soundfield GeneratorCHARACTERISTICSLevel Left Front L = 0 dBd, R = Off 0 dBdT T Right Front R = 0 dBd, L = Off 0 dB ..
SSM2015P ,+-18V; low noise microphone preamplifierGENERAL DESCRIPTION The SSM-2015 is an ultra-low noise audio preamplifier particu- larly suited ..
SSM2017 ,Self-Contained Audio PreamplifierAPPLICATIONSREFERENCEAudio Mix ConsolesIntercom/Paging SystemsPIN CONNECTIONSTwo-Way RadioEpoxy Mi ..
SSM2017 ,Self-Contained Audio PreamplifierSPECIFICATIONSfications apply at T = +258C.)AParameter Symbol Conditions Min Typ Max UnitsDISTORTIO ..
STA811M , Separate Excitation Switching Mode Regulator ICs with Flywheel Diode
STA821M , Separate Excitation Switching Mode Regulator ICs with Flywheel Diode
STABP01 ,BASH DIGITAL PROCESSORSTABP01DIGITAL PROCESSOR■ BASH® LICENCE REQUIREDDESCRIPTIONThe STABP01 processor is used to control ..
STABP01D ,BASH DIGITAL PROCESSORBLOCK DIAGRAMUVLO: 7V = on 5V = off10V-Q R+VREF 1V INTERNAL- 1V POWER SUPPLY1CIRCUITQ SO ..
STAC9708 , Multi-Channel AC97 Codec With Multi-Codec Option
STAC9723T , Stereo AC 97 Codec With Multi-Codec Option

SSM2000P
HUSH Stereo Noise Reduction System with Adaptive Threshold
REV.0HUSH Stereo Noise Reduction System
with Adaptive Threshold
PIN CONFIGURATION
24-Lead Plastic DIP
24-Lead SOIC
TOP VIEW
(Not to Scale)
NC = NO CONNECT
L IN
R IN
L VCF C1
L VCF C2V+
ACOM
VCA PORT
VCF DET IN
SUM OUT
VCA DET IN
VCF DET CAP
VCA DET CAP
DEFAULT 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 DolbyB® 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
APPLICATIONS
Auto Radio Sound Processing
Multimedia PC Sound Cards
Television Sound Processing
Cassette Tape Players
AM/FM Receivers
Telephone & Wireless Links
Professional Audio
Figure 1.Typical Basic Application
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.
DolbyB is a registered trademark of Dolby Laboratories, Inc.
HUSH is a registered trademark of Rocktron Corporation.
NOTESNR in defeat mode.
Specifications subject to change without notice.
SSM2000–SPECIFICATIONS(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.)
Figure 3.Dynamic Filter Characteristic (For CF = 0.001 μF
Defeat Mode)
INPUT
LEVELOUTPUT
LEVEL
Figure 2.Downward Expander Attenuation Characteristic
(In dBt; 0 dBt = Threshold)
PIN DESCRIPTION
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
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 (TJ) . . . . . . . . . . . . . . . . . . . . . +150°C
Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . . +300°C
ESD RATINGS
883 (Human Body) Model . . . . . . . . . . . . . . . . . . . . . . 2.5 kV
EIAJ Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 V
ORDERING GUIDE
PACKAGE INFORMATION
NOTEθJA 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..
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.
JA1
RCA
LEFT IN
JA2
RCA
RIGHT IN
1kΩ
510Ω
THRESHOLDR12
20kΩ
20kΩ
U1-C
OP482
R17
20kΩ
U1-B
OP482
1N4148
Figure 4.Typical Dual Supply Application and Test Circuit
INPUT SIGNAL – Vrms
THD + N – %
0.1
Figure 6.THD+N (%) vs. Input Signal
FREQUENCY – Hz
0.00130k100
THD + N – %10k
0.01
Figure 7.THD+N (%) vs. Frequency
FREQUENCY – Hz
–1220200k100
GAIN – dB10k100k
–10
Figure 8.–3 dB Bandwidth
INPUT SIGNAL – dBu
@ 1kHz
OUTPUT SIGNAL – dBu
–40
Figure 9.Output vs. Input Characteristics (With Different
Adaptive Threshold Voltage, Pin 17)
VCA CONTROL VOLTAGE (Pin 7) – V
L, R CHANNEL OUTPUT – dB0.511.522.5
–60
Figure 10a.Channel Output vs. VCA Control Voltage (Pin 7)
FREQUENCY – Hz80k100
GAIN – dB10k
–17.7
Figure 10b.VFC Characteristics (Simulated Noise Level
90 mV rms with Different Frequency) Applied through a
CHANNEL OUTPUT – dB
Figure 11.Channel Output vs. Frequency for Different
VCA Control Port Voltages
FREQUENCY – Hz
–7020k1001k10k
CHANNEL SEPARATION – dB
TA = +25°C
VS = ± 4.25V (Pin 5, 20)
DEF THRESHOLD = 0V (Pin 14)
DEFEAT = ON (Pin 16)
MUTE = OFF (Pin 17)
RL = 100kΩ
VIN = 300mVrms SINE WAVE (Pin 1 or 2)
UNSELECTED INPUT = 0V (Pin 1 or 2)
Figure 12.Channel Separation vs. Frequency
FREQUENCY – Hz
–10030k100
MUTED OUTPUT LEVEL – dB10k
–95
Figure 13.Muted Output Level vs. Frequency
FREQUENCY – Hz
–8030k1001k10k
PSRR
– dB
Figure 15.PSRR– vs. Frequency
SUPPLY VOLTAGE – V4206
SUPPLY CURRENT– mA1012141618
Figure 16.Supply Current vs. Supply Voltage
SSM2000–Typical Performance Characteristics
APPLICATIONS INFORMATION
Introduction
The SSM2000 is a dual channel audio noise reduction IC which
reduces noise through a combination of variable filtering and
downward expansion in conjunction with a unique adaptive
noise threshold detector. These two techniques yield an overall
noise reduction of up to 25 dB on AM and FM radio, open reel
and cassette tape, CD, Dolby B encoded programming, broad-
cast studio-transmitter links, telephone lines, and other audio
sources without the need for any additional manual adjustment.
The HUSH Noise Reduction System as implemented in the
SSM2000 has been shown to substantially reduce noise in PC
multimedia, intercom systems, teleconferencing systems, mobile
communications, automotive audio, home stereos and televi-
sions, and other consumer and professional audio applications
while preserving full signal fidelity and transparency.
A brief explanation of the nature of audio signals is useful before
discussing the details of the SSM2000’s operation. First, audio
signals have both amplitude and frequency content. Music and
voice are created by changing both the amplitude and frequency
of sound waves as shown in Figure 17. Second, the highest
audio signal amplitudes typically occur at low frequencies
(100 Hz–1 kHz) and taper off exponentially as frequency in-
creases. Third, when an audio signal is recorded, audio noise is
also generated. This noise is the white noise “hiss” or waterfall
sound that is easily heard on taped material. Audio noise for a
given source and bandwidth does not, in general, change with
frequency or amplitude. However, noise levels do change be-
tween different sources, because of differences in recording
equipment, media, and the surrounding environment. Fourth,
psychoacoustic effects mask noise that occurs at or near the fre-
quency of the audio signal. Finally, audio noise is usually con-
sidered to be most objectionable in the 3 kHz–8 kHz bandwidth
region.
AMPLITUDE
FREQUENCY
Figure 17. A Frequency-Amplitude Plot of the Audio
Envelope
An analog noise reduction system must first distinguish between
the desired source material and the undesirable noise. It must
then attenuate the noise while leaving the source material unaf-
fected. One approach to noise reduction is to assume that signal
below a predetermined amplitude is noise, and to then attenuate
the noise by using a Voltage Controlled Amplifier (VCA). A
variation of this noise reduction method is found in Dolby B
cassette tape systems. This method achieves about 10 dB of
improvement in signal-to-noise ratio (SNR). This system incor-
porates a high-frequency compressor on the recording side, and
occurs above the highest signal frequency. This noise reduction
method utilizes a Voltage Controlled Filter (VCF) and is the
basic method of operation in the DNR® system, which provides
about 10 dB of noise reduction. The HUSH system shown in
Figure 34 combines elements of both of these techniques to
achieve 25 dB of noise reduction, and also has significant
improvements.
Figure 18.SSM2000 Block Diagram (One Audio Channel
Shown)
Recalling that the noise floor changes with different audio
sources due to recording equipment, media, and the environ-
ment, we realize that fixed threshold approaches cannot yield
optimal results. The HUSH Noise Reduction System incorpo-
rates an automatic noise threshold detector that senses these
changes and adapts the VCA and VCF to become more or less
aggressive depending on the amplitude of the noise floor. To
determine the amplitude of the noise floor the SSM2000 as-
sumes that the averaged amplitude during short periods of no
audio is equal to the noise floor. This assumption works well in
audio applications, but does have implications for evaluation
and testing that are discussed in the “Evaluating the SSM2000”
section.
Variable Low-Pass Filtering
The audio signal is first passed through a single-pole low-pass
Voltage Controlled Filter (VCF). Both the Left and Right
VCFs are controlled by a detector which places their cutoff fre-
quencies just beyond the highest audio signal frequency. Since
the highest audio signal frequency constantly changes, the
VCF’s cutoff frequency must also change in concert with the
audio signal to avoid attenuating desired signal.
For example, with signal levels below the filter threshold (pre-
sumed to be mostly noise), the VCF shuts down to about 1 kHz,
providing noise reduction in the critical 3 kHz– 8 kHz band, as
Figure 19 illustrates. The VCF progressively “opens up” as
higher frequency amplitudes are detected at the inputs. The
VCF’s cutoff reaches 20 kHz when the high frequency signal
amplitude is 30 dB above the threshold. At this point the VCF
is acoustically transparent. The VCF’s cutoff frequency range is
between 1 kHz to 35 kHz. The minimum range of the VCF is
limited to 1 kHz for two reasons: one, to avoid high frequency
loss at the leading edge of transients, because the lower the
minimum cutoff the longer it takes the VCF to slew “open,” and
two, noise is most objectionable at mid and high range frequen-
SSM2000
AMPLITUDE
FREQUENCY
Figure 19.A Frequency Amplitude Plot Illustrating the
Noise Reducing Effect of the VCF
The SSM2000 has been designed to minimize control feedthrough.
Control feedthrough may cause an audible output as the internal
control lines of the VCAs and VCFs are changed rapidly. This
feedthrough is the cause of many of the unpleasant artifacts
prevalent among noise reduction systems and is often due to
parasitic capacitance and mismatches within the IC. This speci-
fication is important for the VCA and VCF, but the VCF is the
most susceptible because it operates at constant dc gain. The
solution incorporated into the SSM2000 to reduce control feed-
through has been to convert from single-ended to full differen-
tial at the signal input and convert back again at the output
buffer. Because the audio path through the VCA and VCF are
fully differential, control feedthrough is determined purely by
mismatches with no systematic errors. The slight penalty to be
paid for a fully differential system, besides extra complexity, is
that the external VCF capacitors (1 nF recommended) now re-
quire two pins each instead of one. Careful attention to VCF
capacitor matching and layout symmetry reduces control
feedthrough to better than 40 dB through the signal path.
Downward Expander
After the audio signal passes through the VCF, it is then differ-
entially sent to the VCA. The VCA is characterized by a
downward expander transfer function as shown in Figure 20.
Attenuation begins at output levels below the internal threshold
at an effective rate of 2.2 dB/decade. Therefore, audible noise
is attenuated when source material is not present. Conversely,
when audio source levels are at or above the threshold, the VCA
is set to unity gain. Because of well documented psychoacoustic
effects, it is valid to assume that at high audio amplitudes audio
noise is being masked by the audio material. The control infor-
mation that is required for the downward expander to function
properly is provided by the internal VCA detector side-chain cir-
cuitry common to both the L and R channels.
Previous downward expander circuits have often used a higher
ratio than 2.2 dB/decade to provide impressive noise reduction
figures (50 dB or more) in the absence of signal information.
However, in most applications, such severe noise gating is to-
tally pointless, and actually exacerbates the effects of VCA con-
trol feedthrough, since control feedthrough is not attenuated as
the VCA shuts down. For this reason, the maximum VCA at-
tenuation in the SSM2000 is limited to 15 dB. In addition, the
“smooth” roll-off of the downward expander eliminates any
audible artifacts resulting from this type of noise reduction. In
contrast, many noise reduction system employ gates and com-
a poor quality connection is very near the gate’s switching level.
The Mute function (Pin 17) can override the VCA controls, as
shown in Figure 5. When mute is active (HIGH), it pulls the
VCA to maximum attenuation. An 85 dB professional quality
mute under worse case conditions can be expected over most of
the audible frequency range as shown in Figure 13. Mute over-
rides both the internal VCA control coming from the VCA De-
tector and the external VCA control port (Pin 7). The external
VCA control port is additive in nature to the internal VCA con-
trol signals; therefore, noise reduction and volume control may
occur simultaneously in the SSM2000. The VCA control port
allows the gain of the VCA to changed externally at approxi-
mately 22 mV/dB, where 150 mV is equal to 0 dB, as shown in
Figure 10a.
Figure 20.Downward Expander Transfer function
VCF Detector
Both the VCF and VCA detectors are amplitude detectors and
identical in every way. The applied input signals to the detec-
tors must be preconditioned for the detector circuitry to give
the information that is required by the L and R VCFs and
VCAs. Figure 21 is a schematic of the recommended precondi-
tioning filters for use with the VCA and VCF detectors.
Figure 21.The Recommended Signal Preconditioning
Filters for the VCA and VCF Detectors
The VCF detector is fed by 3 × (L+R)/2 averaged input signal
processed by a three-pole high pass filter with a –15 dB point at
10 kHz. In Figure 22, the response of the VCF’s 3-pole filter is
shown. The VCF preconditioning filter performs two func-
tions: first, it eliminates the large amplitude, low frequency au-

Partno	Mfg	Dc	Qty	Available	Descript
SSM2000P	AD	N/a	39	avai	HUSH Stereo Noise Reduction System with Adaptive Threshold