Stem mastering is mastering where the content provided to the mastering engineer is separated into multiple stems rather than one stereo premaster. This is useful for vocal tracks, or instrumental tracks with complex instrumentation. Stem mastering offers many benefits over stereo mastering due to the increased control of the content being mastered. Stem mastering is often considered a lower cost alternative to mixing. In many cases, stem mastering can offer comparable or better results than hiring separate mixing and mastering engineers, as stem mastering allows the mastering engineer to mix into the mastering compressor.
Analogue, outboard compressors are always used on big budget vocal tracks due to their superior color and compression characteristics relative to plugins. The transformers and tubes inherent to this gear simply compliments recorded content. Stem mastering allows your mastering engineer to utilize analogue vocal chains at a much lower budget than separate mixing mastering.
Better Bass Control
A frustration mastering engineers hear frequently from producers is that they have difficulty getting the sub bass right in their mixes. This issue is mainly due to limitations of the smaller monitors and less acoustically treated rooms used in production. With production setups it’s simply not possible to hear what’s happening in bass frequencies, and therefore not possible to create a mix that accurately translates in these frequencies. Mastering monitors are specifically designed to accurately reproduce the lowest frequencies in the human hearing range and can cost tens or even hundreds of thousands of dollars. In a typical stem mastering preparation, all instruments with bass content are printed separately. This allows your mastering engineer to properly balance all the bass content of your mix, in a listening environment that allows your engineer to hear exactly what’s going on. For content with critical bass, you’ll always enjoy better results with stem mastering.
In a big-budget recording studio, every single instrument is routed out of the computer and into a channel on an analogue mixing console. This mixing console contains equalizers and compressors, and sums all the individual tracks into one stereo mix. In large part, the higher fidelity sound of big budget records is due to this analogue summing process. There are small nuances and colors added to each individual instrument by the mixer, offering a distinctively analogue aesthetic which simply isn't possible when mixing inside a DAW. Stem mastering allows your mastering engineer to sum your mix in the analogue realm, offering the same benefits of having your track mixed in a big-budget studio.
A typical stem preparation for stem mastering will include separate bass instruments, drums, vocals and the remaining instruments.