A compressor is a dedicated software plugin or hardware unit used to apply compression: reducing the volume of loudsoundsor amplifying quiet sounds by narrowing or "compressing" anaudio signal'sdynamic range. Compression is commonly applied in the mixing and mastering stages of EDM production.
Compressors often haveattackandreleasecontrols that vary the rate at which compression is applied and smooth the effect.
Software compressors are often capable of sidechaining (or "ducking") sound as well.
This is a hard-knee compressor. Note that once the threshold of -22.5 dB isreached, the compressor has a sharp slope on the output portion of the graph (The X Axis is the input, the Y Axis is the output)
This is Ableton's standard compressor. See how It has the same essential controls as the Logic compressor, save for the "Opto" envelope option. Opto stands for Optical, a type of compressor that very basically uses a light and a light sensitive resistor to determine how much compression to apply. The more signal that goes through the light, the more the compressor acts. Due to the nature of basically using a lightbulb to control the compression, optical compressors tend to have very slow response times in comparison to other types.
This is a Teletronix LA-2A Leveling Amplifier. This is an analog, optical compressor. Note the two options given, gain and peak reduction. The peak reduction knob controls how much compression is applied to the track, but the numbers don't correspond to a direct ratio.