The Compressor decreases the dynamic range of the audio signal by making the loud parts of the sound quieter. It works by reducing the level of the sound that's above the threshold by the ratio amount.
RMS/Peak - RMS (root mean square) or peak level detection. Peak detection is for limiting.
Auto Makeup Gain - Raises the output level by the total gain reduction amount.
Threshold - Gain reduction starts above this level.
Ratio - The amount of gain reduction. Below 2:1 is mild compression. Above 10:1 is limiting.
Soft Knee - How gradual the compressor starts working below the threshold.
Attack - The time it takes for the compressor to start working.
Smooth - Smooths the attack and release transitions. 0, 1, 2 and 3.
Release - The time it takes for the compressor to stop working.
Output Gain - The amount of gain applied to the output signal. The LED shows when it's over 0 dB.
Clip - The type of clipping used on the output signal. Soft (+2, +4, +6 dB) and hard at 0 dB.
Meter - Shows the amount of gain reduction.
If the compressor doesn't seem to be working, try lowering the Threshold.
If it's compressing too much, try raising the Threshold or lowering the Ratio.
If it doesn't sound natural when the compressor is attacking, try increasing the Attack time.
If it's "pumping" or "breathing", try increasing the Release time.
For upward compression, use the Expander and click on the upward compressor button.