What is mixing and why is it so important? Once an engineer has completed the task of editing, he will generally begin work on mixing the audio. This is where the engineer, in essence, carves out a section for every instrument in the stereo spectrum.

Here are some other things that begin to happen in the mixing process:

1. Tracks are panned. This involves placing a particular track or instrument in the stereo spectrum (left, right, and center). It is possible to do a lot of fine tuning here. However, there are many engineers who opt to have about 5 points in the stereo spectrum in which they distribute the tracks. In other words: far left, left middle, center, right middle, far right. Guitar tracks, for example, are typically placed on the left or right sides of a mix.
2. Track levels are adjusted. After the tracks have been recorded, it is still possible to adjust their overall levels (or volume) in the mix. This is perhaps the most basic of all mixing techniques. Vocals are generally loudest in the mix, while other instruments are adjusted accordingly. At this stage, some engineers will also automate tracks. This involves boosting or cutting an instrument's level at a particular point in the mix. For example, a guitar track might be boosted if it goes from a rhythm part to a lead. A vocal track might be automated if the vocalist got a particular syllable louder than intended.
3. Effects are applied. Reverb, echo and delay are used to give the illusion of depth; this is especially useful when parts of the song have been recorded in a "dead space". EQ is used to carve out an instrument's sound. It is much like a guitar amp that has a treble, mid, and bass knob. Each of these knobs or parameters is adjusted in order to achieve different sounds. Compression is used to create a consistent dynamic level in an instrument. For example, a vocal part might vary from quiet all the way to loud. Sometimes, in order to smooth out the levels between the huge discrepancies in the dynamic spectrum, compression will be used. Sometimes, however, compression is not used at all, in order to keep more of the dynamics. There are a variety of other effects that are sometimes applied.

We've only scratched the surface here, but those are some of the things that go in to mixing a track.