Microphone Preamplifier with
Variable Compression and Noise Gating
Complete microphone conditioner in a 14-lead SOIC package
Single 5 V operation
Adjustable noise gate threshold
Compression ratio set by external resistor
Automatic limiting feature—prevents ADC overload
Adjustable release time
Low noise and distortion
20 kHz bandwidth (±1 dB)
Computer sound cards
Public address/paging systems
Guitar sustain effects generators
Computerized voice recognition
Karaoke and DJ mixers
SSM2166 can be programmed with a fixed gain of up to 20 dB;
this gain is in addition to the variable gain in other compression
settings. The input buffer can also be configured for front-end
gains of 0 dB to 20 dB. A downward expander (noise gate) prevents
amplification of noise or hum. This results in optimized signal
levels prior to digitization, thereby eliminating the need for
additional gain or attenuation in the digital domain that may
add noise or impair accuracy of speech recognition algorithms.
The compression ratio and time constants are set externally. A
high degree of flexibility is provided by the VCA gain, rotation
point, and noise gate adjustment pins.
The SSM2166 is an ideal companion product for audio codecs
used in computer systems, such as the
The SSM2166 is
available in a 14-lead SOIC package and is guaranteed for
operation over the extended industrial temperature range of
−40°C to +85°C.
COMP RATIO = 10:1
COMP RATIO = 2:1
The SSM2166 integrates a complete and flexible solution for
conditioning microphone inputs in computer audio systems. It
is also excellent for improving vocal clarity in communications
and public address systems. A low noise, voltage-controlled
amplifier (VCA) provides a gain that is dynamically adjusted by
a control loop to maintain a set compression characteristic. The
compression ratio is set by a single resistor and can be varied
from 1:1 to over 15:1 relative to a user-defined rotation point;
signals above the rotation point are limited to prevent overload
and to eliminate popping. In the 1:1 compression setting, the
COMP RATIO = 1:1
Figure 1. Compression and Gating Characteristics with 10 dB of Fixed Gain (The
Gain Adjust Pin Can Be Used to Vary This Fixed Gain Amount)
FUNCTIONAL BLOCK DIAGRAM AND TYPICAL SPEECH APPLICATION
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Fax: 781.461.3113 ©1996–2008 Analog Devices, Inc. All rights reserved.
COMP RATIO SET