REV. A

SSM2165

–9–

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

300

45

COMPRESSION

REGION

LIMITING REGION

NOISE GATING REGION

0.5

2

30

40

INPUT – mV

Figure 18. Transfer Characteristic

SUMMARY

We have implemented the transfer characteristic of Figure 18.

For inputs below the 500

µV 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.