Audio level compression, also called dynamic range compression, volume compression, compression, limiting, or DRC (often seen in DVD player settings) is a process that manipulates the dynamic range of an audio signal. Compression is used during sound recording, live sound reinforcement, and broadcasting to improve the perceived volume of audio. A compressor is the device used to create compression.

Wikipedia link

When you start changing the dynamic range of an audio signal, the perception of frequencies for the human ear is affected as well. Because of this a compressor can be used as an EQ.

So if a single-band compressor (using one compressor for the whole frequency-range) radically changes the EQ of a sound, using a multiband-compressor will create almost endless possibilties.

Here are a few tips how to really master the compression techniques:

• Don’t use too many different compressors, just stick to one or two and really explore the way they are affecting your sound
• Use nothing but compressors to change the frequencies of your signal, don’t use any EQ!
• Be patient, make mistakes and learn from these mistakes

When you have mastered how to use compressors, you might start using a bit of EQ as well, but using both at the same time might be confusing when you really want to learn how a compressor can affect sounds.

And last be not least: because compressors are changing the dynamics of sound, a compressor can add some ‘air’ to your track. So using lots of them, for example one per channel, can totally change the whole perception of your mix. I think it’s a journey which is well worth to spend some serious life energy on!

Good luck exploring!