Imagine the ideal scenario: a Mastering of a very good stereo mix. You have as your starting point a flat mix which represents the very best modern recording techniques; enough headroom, a good signal-to-noise ratio, a full and natural frequency response, and most importantly a perfectly balanced blend of well recorded instruments and/or voices.
The mastering engineer’s objective is to iron out any minor humps (bumps or holes in the frequency spectrum) glue the mix together or add impact with some compression maybe, and generally make sure it sounds at least as good out there in the real world as it did to you in the mix studio when you laid it down. In our perfect example, this is of course not a problem at all. Every small change will bring the mix to a better! “A good mix bring a good Mastering !”
In real life, that ideal scenario is not common … a little problem in the mix (e.g. edgy guitars) and the correction of the problem will lead to changes throughout the mix and other instruments (for example at the cymbals level …)! Mastering come here to a limit.
The solution is to separate the song/ the mix in “STEMS”!
What is a “STEM”
By definition, the “STEMS” are a breakdown of the mix, which when added back together at equal volume create the mix as if you had presented it as a single stereo file. All “STEMS” for a given master should be the same length, so that when they are lined up side by side, the mix of elements are perfectly in phase, and they should also contain the effects (unless you choose to present the effect returns in their own “STEM” separate).
A “STEM” can be:
- A group of instruments (For example: Drums, guitars, etc … but can also be different instruments together)
- A single instrument (eg Bass, the main vocal, …)
- Or sometimes, just the effects (eg, grouping all the effects)
A classic example of stem would be: Drums, Bass, Vocals, the rest! We will try to keep at least a separation between: Percussion, bass and harmony. having access to these three elements separatly can be very useful in mastering.
One can imagine many possibilities until having one instrument by “STEM” … just keep in mind that thanks to the “STEM MASTERING” we will have more flexibility and we will be able to correcct every little detail of each “STEM” !