Stem mastering sits between full mix mastering and mixing from scratch.
It gives the mastering engineer more control than a stereo bounce, without requiring the full multitrack session.
For many projects, it is the most practical way to get a high-quality master when the original mix has problems that a standard mastering chain cannot cleanly address.
This post is part of the Complete Guide to Audio Mastering.
What is Stem Mastering?
In standard mastering, you send a single stereo mix file. The engineer applies a chain of EQ, compression, and limiting to that stereo file and delivers the final master.
In stem mastering, you send multiple grouped stereo files, called stems, instead of one mixed file. Common stems include: drums and bass together, instruments, vocals, and any additional elements like synths or effects.
The mastering engineer processes each stem individually before combining them and applying the final mastering chain.
This means the engineer can adjust the relative balance of the drums versus the vocals, compress the low-end stem differently from the vocal stem, and deal with problems in one area of the mix without affecting the rest.
It is significantly more control than standard mastering, but it also requires more work from both sides.
When to Use Stem Mastering
Stem mastering is not necessary for every project.
If your mix is well-balanced and the only thing needed is tonal polish and loudness optimization, standard mastering is the right choice.
Stem mastering makes sense when:
- The mix has balance problems that a standard mastering EQ cannot cleanly fix without affecting other elements
- The low-end is inconsistent and would benefit from independent processing
- The vocals need to be slightly louder or quieter relative to the rest of the mix without going back to the full session
- You want more nuanced control over the final sound than a stereo file allows
How to Create Stems Correctly
The most important rule in stem mastering is that the stems must sum to exactly the same sound as the original mix.
This is not optional. If the stems sound different when combined than the original mix, you are no longer mastering the same record.
You are creating a different one.
To check this, export all the stems and import them into an empty session. Route them all to a bus and listen.
The combined stems should sound identical to the original stereo mix.
If they do not, something was exported incorrectly, a plugin was not captured, or effects were not printed to the correct stems.
When creating stems, always print all effects and processing onto the stems.
This means that reverbs, delays, saturation plugins, and any other effects that were active in the mix must be included in the exported audio.
Do not strip the processing and send dry stems. The mastering engineer needs to work with the actual sound of the mix, not a raw version of it.
Common Stem Groupings
The specific groupings depend on the project.
There is no fixed rule, but the most practical approach is to group elements by how they would need to be treated differently from each other.
Common groupings:
- Low end: Kick drum and bass together on one stereo stem. These two elements are the most important to balance independently in the mastering stage.
- Drums (without bass): The rest of the drum kit, including snare, hi-hats, toms, overheads, and room mics.
- Instruments: Guitars, keys, synths, and any other harmonic or melodic elements.
- Vocals: Lead vocal, backgrounds, harmonies, and adlibs. Some engineers separate lead vocals from backgrounds.
- Effects: Any standalone reverb or delay returns that are not already printed onto their source tracks.
Fewer stems means less flexibility but less complexity. Four to six stems is a practical range for most projects.
Stem Mastering vs Mixing Again
There is a limit to what stem mastering can fix.
If the individual elements within a stem sound wrong, stem mastering cannot address that.
For example, if the kick drum within the low-end stem is EQ’d badly or clipping, working with the stem as a whole will not fix the kick specifically.
Stem mastering is also not a substitute for going back and fixing a genuinely broken mix.
If the mix has significant problems, the better answer is to return to the multitrack session and fix them properly.
Stem mastering is most effective when the mix is already close to what you want and you just need more control over the balance at the mastering stage.
Cost and Practicality
Stem mastering takes more time than standard mastering, so professional stem mastering services charge more than standard mastering.
If you are mastering your own music, the extra cost is your own time, which is worth considering. Standard mastering is faster and often sufficient.
If you are working with a professional engineer and your mix has specific balance issues you want addressed without going back to the mix session, stem mastering is worth the additional cost.
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