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Mastering Audio is known in the music industry as a slightly dark art - essentially it makes an existing track sound better, while preserving the original intention of the producer. There is a lot of fine-tuning and subtle work.
You won't/shouldn't really notice the mastering as such, unless it touches either extremes of quality - really amazing, or really terrible!
The difference between a good master & a great master is often not really very quantifiable.... A great one just has "something special" about it, which noticeably adds to the overall quality, but isn't always easy to pin down why.
An average master can quickly become subconsciously grating to the ears, sound flat and lifeless, or have problems with the EQ that is revealed on different playback systems. It's not always the mastering at fault here though, as some mixes have problems that could be optimized first for a better final result.
Mastering is like most things in life - the better the input, the better the output.
So today we are going to talk about Stem Mastering, which can help optimize a few of the most demanding parts of a mix as an integral part of the mastering job.
What is Stem Mastering?
Stem mastering is like a mini-mix combined with mastering. It can optimize a mix that's already great, or correct a few difficult elements and rescue a mix that would otherwise have major issues, leading to a non-ideal end result.
It is the process of sending certain parts of your mix separately, so the mastering engineer can adjust key elements individually during the mastering process if needed.
Often during mastering certain elements get highlighted and mix flaws revealed. It's really useful for the engineer to be able to adjust these aspects on the fly to get the best end result.
For example, there may be an instrument that overlaps the frequency band of a vocal performance, and during the mastering process the vocal needs a little EQ tweak... but this makes the other instrument sound harsh, or vice-versa and adjusting a harshness in the other instrument dulls the vocal. It would be helpful to be able to adjust these elements with a little more separation (there are A.I. tools that can be useful, but they are hit-and-miss sometimes).
When do you need stem mastering?
Low-end problems (kick, bass, sub):
Many technically excellent, talented producers don't have the luxury of a fully accurate listening environment which can cause problems balancing their low-end. Matching the kick & sub levels between each other is a very common problem which relies on both accurate monitoring AND environment.
There are a few A.I. driven tools on the market which are helpful, but in my experience they don't quite get it right most of the time. I often use one in my chain, but the majority of the time (90%+) I don't actually follow its suggestions completely, and use it more as a quick way to check another approach, like a second pair of ears to ask an opinion of. The neutral room + human ears still give the best results.
Vocal balancing:
A vocal is one of the most tricky parts to make sit naturally inside a mix, and because we all know the sound of a human voice intimately, a vocal that's not quite blended perfectly is the easiest way to make an otherwise amazing mix go downhill. So many talented producers find getting the vocal to sit right the most challenging part of a mix. If this is you, you are not alone!
The highest level mix optimisation:
Even if your mix is pretty damn great already, and you just want to get the most optimized mastering possible, then stem mastering can make that happen. It gives the engineer full flexibility to tweak micro aspects of the master and get really precise for ultimate results.
Weak sounding drums:
A classic problem, especially when recording live drums. The track is banging, guitars sound huge, vocal is great, bass is thumping, but the drums sound weak and let the whole track down. By sending the drums separately we can give them the extra push needed to fatten them up.
Any instrument that isn't "sitting right":
Don't let it annoy you. Send it separately as a stem and let the engineer fix this in the mastering.
How To Set Up A Stem Master?
It is good general practice when mixing a song to group various elements to different subs/buses before the master output fader. This is helpful for many reasons: You can pull down just 1 fader to adjust all the drum channels for example, or effect all vocal channels with 1 effect. Or send different parts of your track to 1 reverb, or many other cool things beyond the scope of this article. Sending grouped parts to buses is also useful in optimizing your gain structure to avoid clipping. It's generally a good thing to do!
When you export your mix, you will choose the option that exports all these different buses separately - these individually grouped wav files are your stems.
There's no specific rules to what parts to use as stems - it will vary depending on how many instruments are causing issues, or how complex your track is.
For a rock stem mastering job, you might have the following stems:
Or for an electronic track:
This is a common stem setup for a dance track:
Tricky vocal?:
Lots of options! Note how sometimes I've grouped them as "hard" & "soft" sounds - really it depends on the track and what elements work most naturally together.
Once you have chosen the best stem configuration for your mix, export them ("Export - Buses" or similar), then load them up in a new project and make sure they play back exactly the same as your normal stereo mix.
Send them all separately in a zip file to your mastering engineer, along with a regular stereo copy of your full mix as a reference so the engineer can check all is well.
Final thoughts:
Stem mastering is not essential for every track at all. But it can make the difference between a good final result and a fantastic final result.
It doesn't have to be expensive either. For example, at Fat As Funk Mastering, you can add a stem for just £7 on top of the mastering cost.
Next time you have an element of your mix that is not quite "there"... try stem mastering and see how much difference it can make.
https://fatasfunk.com/product-category/stem-mastering/
About the author:
Loz Gill has been a full-time mastering engineer at Fat As Funk since 2006.
