Perhaps even more important than equalization, the process of making instrument volume levels even throughout the duration of a song is paramount to achieving a great mix.
Volume levels should be somewhat dynamic for creative purposes, but for many instruments–particularly bass guitar and vocals–the volume should be relatively even. Otherwise, you risk listeners ability to hear every word or every note.
So…how do we do this? There are two major ways. First, you could go through and even out the levels with manual fader riding. But…that takes a lot of time and time is money as they say. So…what else? Compression.
Compression is basically automatic gain riding. You set how the compressor should react to a signal that goes over a set level (called the Threshold) with attack and release controls.
You can also use a compressor creatively. Here are a few video tutorials to watch on the subject of compression:
If that tutorial wasn’t good enough, watch this one:
The type of compressor you use is also important. Once you learn the basics with a standard digital compressor that is built into most DAW software, it’s time to move onto hardware emulations. Watch this video for a brief overview of the compressors top audio engineers use:
There are also plugins that automatically ride volume faders for vocals and bass such as
Finally, here are some videos on how to do parallel (New York) and serial compression tricks: