GAIN REDUCTIONIn order to assure a smooth transition between periods of gain reduction, compressors feature both attack and release time parameters to be set by the user. Attack time determines how long the compressor takes to reduce the gain once the input signal has passed the threshold, while release time determines how long the gain takes to return to it’s previous level after the input signal has fallen back below the threshold. With aggressive attack and release times, the effect of a compressor is quite audible, in that it causes the signal to “pump”. More modest attack and release settings, on the other hand, will make the effect of the compressor far less noticeable.
One way to further reduce the audible effect compression has on an audio signal is the knee setting. A soft-knee compressor will gradually ramp up the compression ratio as the audio signal approaches the threshold, and once the threshold is reached the full compression ratio will be reached. The beauty of a soft-knee compressor is its ability to work with a higher degree of finesse, yielding an incredibly smooth and transparent result, as gain reduction is introduced gradually over time. That said, there are situations in which we want compression to be more aggressive, such as when we are using it to create a desired effect, such as gain pumping. In these situations, harder knee settings will be preferable. For example, in electronic dance music, deliberate gain pumping is often used in order to help create a bouncing groove with a 4/4 beat.