SSM2165-2P AD [Analog Devices], SSM2165-2P Datasheet - Page 9

• Manufacturer Part Number: SSM2165-2P
• Description: Microphone Preamplifier with Variable Compression and Noise Gating
• Manufacturer: AD [Analog Devices]

rms detector averaging time, and the decay time of the gate.
Both compression ratio and decay time are usually determined
by critical listening to the intended audio input.
STEP 7. Record Values
With the power removed from the test fixture, measure and
record the values of the R
REV. A
300
45
Figure 18. Transfer Characteristic
NOISE GATING REGION
0.5
COMPRESSION
2
REGION
COMP
INPUT – mV
and C
30
AVG.
40
LIMITING REGION
–9–
SUMMARY
We have implemented the transfer characteristic of Figure 18.
For inputs below the 500 V noise gate threshold, circuit and
background noise will be downward expanded (gain-reduced) at
a ratio of approximately 1:3. That is, a –1 dB change in the
noise will result in –3 dB decrease at the output. Above thresh-
old, the signal will increase at a rate of 1 dB for each 2 dB input
increase, until the rotation point is reached at an input of
approximately 40 mV. In the limiting region, the compression
ratio increases to approximately 15:1. That is, a 15 dB increase
in input will produce a 1 dB increase at the output, so there will
be little further increase for higher level inputs.
Other Versions
The SSM2165 is an 8-lead version of the 14-lead SSM2166
which is recommended for applications requiring more versatil-
ity. The SSM2166 allows selection of noise gate threshold and
rotation point, and allows the buffer to provide up to 20 dB of
gain. Power-down and mute functions are also built in. Custom-
ized versions of the SSM2165 are available for large volume
users. The wide dynamic range of the SSM2165 makes it useful
in many applications other than microphone signal conditioning
such as a sustain generator for guitars. For further information,
contact your Analog Devices representative.
SSM2165