Mixing is more than just adjusting the volume levels of individual instrument and vocal tracks. Of course, that is a big part of mixing, but it’s by no means the whole story. Mixing also involves:
In addition to volume levels, mixing engineers decide where in the stereo spectrum to place each instrument. Music is recorded and played back in a stereo field, meaning there are left and right speakers and sounds can be placed accordingly. It is imperative for all instruments to be panned to a proper place in order to get a clean mix. Not only does that help individual parts stand out and be heard clearly without infringing on another song element, but it allows for the mix to sound balanced between the left and right channels.
When you layer multiple instruments on top of each other, you start getting a “muddy” sound as they take up the same audio frequencies. A good mix engineer knows how to EQ highs, mids, lows, and everything in between so that a mix will sound “clean” and each instrument takes up only its intended place in the song. It takes a trained ear to recognize when certain frequencies should be cut or boosted for particular tracks.
Guitarists sometimes record with effects, but the vast majority of effects processing goes on during the mixing process. Things like compression, reverbs, delays, and many other effects are chosen and tweaked by the mixing engineer, who helps make what might otherwise be a dull or lifeless recording into something full and lush. Engineers must have a slew of professional quality effects processors and plug-ins at their disposal to ensure a great mix.
It would be nice if mixing was as simple as setting the volume faders in one place and letting the song finish, but unfortunately it’s a lot harder than that. Because different tracks need to be at the forefront of the song at different times–lead vocals here, guitar solo there, etc.–things like volume levels, panning, and effects need to be automated. Automation is what the mixing engineer does to program certain fades and pans into different parts of the song, so that each time it plays, that cool keyboard lick in measure ten will come up to the exact same level every time the mix is played back. This can be a very specific and complicated process, so it’s best left in the hands of a professional!
I hope this post shed a little light on what may have been a slightly mysterious step of the recording process to many musicians. As you’ve probably gathered, mixing is an extremely crucial part of making a great recording, and shouldn’t be phoned for the sake of your song’s future.