The Compressor effect pedal allows for reduction of the dynamic range of the inputted audio signal by narrowing the difference between the high and low levels of volume (amplitude). Compression can be used to make your music sound louder without increasing its peak amplitude. It can be used to make quieter sounds louder while leaving louder sounds unchanged.
threshold - The level above which the signal is reduced.
ratio - Determines the input/output ratio for frequencies above the given threshold.
attack - The attack phase is the period when the compressor is decreasing gain to reach the level determined by the ratio, once the level has fallen below the given threshold.
release - The release determines the length of time the compressor is increasing gain to the level determined by the ratio, once the level has fallen below the given threshold.
gain - Output volume.
peak/RMS - When set to peak the compressor responds to instantaneous changes to the level of the input signal, providing tighter peak control (more hardcore). Using the RMS setting will mean that the compressor will apply an averaging function to the input signal before its level has been compared to the threshold, allowing for more relaxed compression.