Music Mixing: The Stem Mix
What is a stem mix?
A stem mix is a recorded sub-mix of individual tracks. Stems are a flexible way to store mixes in a non-proprietary form (standard audio files). For example, you could create a stem mix of all the drum tracks, another of the guitars, then keyboards, main vocals, and all backing vocal tracks. Blended together the stems are used to form a complete mix. Stems are used a create new mixes, alternate mixes, make limited adjustments to a final mix, and sometimes for more control during mastering.
While sub-grouping1 is one way to create stem mixes, it is not the only way. A stem mix can also be created by simply soloing channels, then recording (or bouncing) the mix output.
Recording, bouncing, or otherwise rendering a mix (including sub-mixes) is often referred to as "printing" the mix.
Music Mixing Elements
The elements (tracks) included and the processing of those elements will impact the flexibility of the stems. Consider the trade offs. Effects can be printed to avoid the need to access the same processing on other systems. To what extent effects are included is really a matter of preference. A few things to consider are:
- How will the stems be used? To make changes, alternate mixes, or construct a final mix?
- Who will use them? An experienced mix engineer may prefer stems with less processing than someone assembling performance tracks on a smaller system.
- Master output compression will not react in the same way with less elements in the mix. Consider bypassing master output processing, applying it when creating a new mix from the stems.
If there's any question about how to process the stems, make multiple versions (backing vocals w/effects, without effects). This may seem time consuming, but may be worthwhile for important projects.
Creating A Stem Mix
Choose an exact starting point and stick with it for all of the stems. Often this means starting at the top of the project/song for each stem regardless of where any performances take place.
If mixing in a workstation (in-the-box) solo the elements for the stem mix, then either:
- Bounce the stem mix to disk using a "Bounce to disk" function.
- Route the output of the entire mix to the inputs of an empty stereo audio track using the software busses or external patching. Mute the output of the record track(s) unless you are sure the output routing will not feedback into the mix or record track. Record the stem mix to the stereo track.
Repeat for other stems.
If mixing on an external mixer:
- Solo the elements for the stem mix on the mixer.
- Patch the main outputs of the mixer to the inputs of an open stereo track or two mono tracks on the multitrack recorder or workstation (DAW) for recording. Mute the output of the record track(s) unless you are sure the routing will not feedback into the mix or record track.
- Record the stem mix.
Repeat for other stems.
- Route individual channels to a sub-group or aux channel
- Route the sub-group (or aux channel) to the record track
- Record the output to create a stem
Using the later method you must be careful that all effects and source material you wish to include are routed to the sub-group, routed to the stem's record track (if using a record track instead of a bounce), or otherwise routed in a manner that will include them in the stem.
Stem mixes create permanent recorded mixed groups of elements that provide some flexibility regardless of what system is later used. The stems can be used with any multi-track system that supports the stem's audio file type, sample rate, and bit depth. This provides the opportunity, with limitations, to create new mix versions from the stems in the future.
1Sub-grouping and sub-mixing in this context refer to similar techniques where a number of channels are combined within the mixer prior to the main output. The term "Grouping" can be somewhat ambiguous sometimes meaning controlled as a group, other times referring to the bussing.