Stem Mastering: When & How to Go Beyond Conventional Stereo Mastering

This is a guest post by Ryan Schwabe. For even more on mastering, try SonicScoop editor Justin Colletti’s new full-length course, Mastering Demystified.

As an artist, producing or engineering your own music can feel very liberating.  It allows you to craft a unique sonic signature for your record without relying on anyone else’s vision.

With a little bit of practice, creating unique tones and productions will come easy to many young producers. But crafting the perfect overall balancethe depth, dynamics and dimension that you hear in a well-engineered song can be more difficult.

Some productions are arranged so well that the engineering details fall into place without much fuss. However, other songs are more difficult, and it can be frustrating to find the perfect balance. The issue can be in your monitoring environment, your speakers, the arrangement, your engineering skillset, or simply how you hear.

The author, Ryan Schwabe, at work mastering from stems.

Conventional audio mastering from a 2-track stereo file can fix a lot of overall balance issues within a mix, but it does not afford a mastering engineer the freedom and flexibility that “stem mastering” can provide.

When warranted, stem mastering allows the mastering engineer to adjust how the kick and bass interact, how the guitars or keyboards blend into the bass, how the snare drum bounces around the vocal or how bright or dull the vocal is in relation to other elements in the mix.

Of course, those elements can be subtly rebalanced in conventional stereo mastering by using multiband compressors, dynamic EQs or mid-side processing, but you can do it with much more precision—and with much less compromise—through stem mastering, a process where the mastering engineer is given access to submixes, or even essential individual instruments.

Not all songs need stem mastering, but if you are in a situation where you are not completely convinced by the sonics of your record, stem mastering can be a simple and cost-effective solution.

In recent years, I have noticed an increasing number of modern artists crafting their productions and mixes on their own, but using stem mastering to put the finishing touches on their projects, rather than starting from scratch with a complete re-mix.

This happy compromise that still affords self-producing artists the freedom to craft the song exactly how they want, without the complexities and cost of hiring a more experienced mixer, while giving the mastering engineer the ability to help craft the spectral balance of the song by processing individual elements.

If you find yourself in that situation where you are determined to mix your own music, but not 100% sold on the sound of your record, stem mastering may be your answer.  If you decide to go this route, below are a handful of quick tips and best practices for printing stems that sound exactly like your final mix.

1) Let’s talk about file formats.

It’s a good idea to print stems at the sample rate of your original session using 32-bit floating point WAV files. Printing at 32-bit float will protect you from any overs that may take place in the session from improper gain staging.

32-bit float files allow you to go over 0.0 dBFS without any hard clipping being printed into the file. The mastering engineer can then attenuate all of the stem files and bring the peak level back below full scale (0.0 dBFS).

2) Let’s talk about the best way to break your tracks up.  

There are a variety of ways to submit stems, from the very simplest option of sending an instrumental mix and an a cappella mix for help with vocal balance to sending separate stereo prints for almost every instrument grouping.

If you are interested in having the mastering engineer get under the hood of your song, I suggest the below track groupings because they provide for the most amount of flexibility while still keeping things simple and manageable:

Stem 1: Kick
Stem 2: Snare
Stem 3: All remaining drums (hats, crashes, toms etc)
Stem 4: Bass
Stem 5: “Music A” (legato or rhythm type instruments)
Stem 5: “Music B” (staccato or melodic type instruments)
Stem 6: Lead Vocals
Stem 7: Background vocals
Stem 8: Complete stereo reference mix

Each stem should be printed complete with all effects processing, including any compression, EQ, time based effects, like reverb or delay, automation, and any bus processing.

(If time based effects tracks are provided separately its difficult to make a instrumental version without vocal reverb included in the instrumental.)

If you are printing multi-mic acoustic recordings, make sure that all those tracks are properly time and phase aligned.

3) Let’s talk about all those plugs you put on your master fader.  

Stereo processing is used (and often abused) in modern music production, and removing it can significantly alter your mix.

If you think it sounds good, then it is good and should remain.  Personally, I love the weird processing people come up with to mangle their music.  However, I generally suggest removing brick wall limiters from the stereo mix prior to mastering.

EQs, compressors or any other effects processors can and should remain.  If the processors are not at all important to your mix and were just added as an afterthought for reference, you can simply remove them and provide a reference mix for your mastering engineer.

Keep in mind that printing individual stems through your master fader will yield different results because your master fader compressor’s threshold is set for the entire song, not individual elements in the arrangement. So this is one place where the individual elements can sound different than the sum of their parts.

If you want to be really certain that the sound of the compressor on the stereo mix stays consistent when you start printing stems, consider adding in the following to your stem-printing process:

1. Bypass the stereo mix compressor and every plugin after it on the stereo mix
2. Bounce to disc and name the file “Mix Key”
3. Import the “Mix Key” back into your session, make sure it is time aligned with your song and then route the output of the key mix to a unused bus
4. Reactivate your stereo mix compressor and send the “Mix Key” bus to the key input of your stereo mix compressor.

This simple extra step will allow you to print stems while maintaining the same gain reduction from when the compressor was being fed the entire mix.

For even more details on the process, please refer to the page 20 of the GRAMMY Producers and Engineers Wing’s document on “Delivery Recommendations for Recorded Music Projects”.

4) OK, now lets actually make the stems.

First, you should organize your session into a logical order.  Drums, then bass, then guitars and keyboards and then vocals.

Mute all of the source tracks (but not the effects returns or busses) and then un-mute each of the track groupings one at a time and bounce them to disk.

Start with un-muting the kick, then bounce from 0 to the end of the song.  This should include all track processing, buss processing, time based effects and stereo master fader processing.  Then, mute this track and move on to your next stem.

One word of caution: If you are using pre-fader sends for any effects sends in your session, then be sure to bypass the effects send as well, as it will still come through even if that track is muted.

As an alternate approach, you can start by making all your source tracks inactive, and then only reactivate those that you want in the current stem. Either way, make sure that all of these stems have the same exact start point. If you are bouncing off line and not able to monitor the stems as they bounce down you may make some mistakes along the way. That is what brings us to the final step.

5) Last thing: Test your stems

This is by far the most overlooked and important part of preparing stems.

Create a blank session in your DAW choice.  Import the stems on their own tracks with the faders at unity.  Does the mix sound exactly the same as you remember when the faders are at unity?   If so, congrats you did it!  If not, go back into your mix session and reprint any the stems that may have turned out wrong.

The above process may seem like a lot of work, but it is important work. Regardless of whether you plan on working with a stem mastering engineer, a stereo mastering engineer or going  DIY, I strongly recommend that you incorporate this process at the end of every project that you complete and release.

Creating stems may not be the sexiest part of being a producer, but as a producer, it is extremely important to future-proof your intellectual property.

Operating systems go out of date, plugin formats change and in as little as three years from now you may not be able to play the DAW sessions that you create today. By stemming your songs, you are preserving your work for future use.

Five years from now, someone may want an edited arrangement of your song for a commercial or film. A label may want to release your project in a new VR format. We simply have no idea how we will consume music ten, fifteen or twenty years from today.

Stems are an integral part of music preservation, regardless of your interest in using stems in the mastering process. The songs you conjure up in your daw deserve to be preserved beyond the delivery formats we are accustomed to today. Stem your songs out, save’em and keep your catalog ready for whatevers next.

Ryan Schwabe is a mastering engineer and a professor of recording arts and music production at Drexel University. Find him at RyanSchwabe.com

For even more on mastering, try the new full-length course from SonicScoop Editor Justin Colletti, Mastering Demystified.

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