Polycom SoundStructure C16 Design Manual page 119

Engaged Compression Ratio
The "attack" portion of the compressor is when attenuation is increased as the signal level crosses the
threshold, and the "decay" portion is when the attenuation is reduced toward 0 dB as the signal level falls
below the threshold. Decreasing the attack time allows the compressor/limiter to work more aggressively
but may also introduce audio artifacts.
Limiters perform just like compressors, but are typically set with higher compression ratios (10:1 or more)
to further limit the dynamic range of signals levels above the threshold.
Using Gates and Expanders
Expanders and gates are another form of dynamics processing that attenuate low level signals and leave
the high level signals alone. This expands or increases the dynamic range of a signal. When the input signal
level falls below the expander's threshold, it applies an amount of attenuation (in dB) equal to the expansion
ratio times the difference between the threshold and the signal level, as shown in the following figure.
Polycom, Inc.
Threshold
Input Level (dB)
No Compression
2:1 Compression
4:1 Compression
10:1 Compression
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