It might help to think of all compression settings (attack, release, ratio and threshold) as ways to squeeze your audio more or less aggressively. This allows you to do things like bring down the volume level of the compressed track without fear that its softer parts will get lost, or bring up the volume level without fear that the loud parts will jump out. In its simplest form, a compressor, whether a hardware unit or a plug-in, will squeeze the audio so that its highs and lows are less pronounced. In other words, compression brings up the really soft spots and tames the really loud spots so that you’re not constantly reaching for the volume fader on your mixing board (or virtual mixing board on your DAW). To keep things simple, I think of compression as a way of evening out the loud and soft parts of any vocal or instrument so that its behavior is a bit more predictable. The terminology was technical in an almost mean-spirited way and I couldn’t make heads or tails of what was being written. When I first started reading about compressors I was hopelessly lost.

How to mix vocals with instrumentals