Explainer: Stem mastering

What is it, how is it different from traditional mastering techniques and is it suitable for you?

Traditionally, the two stages of mixing and mastering are kept completely separate. When preparing a song for the mix stage, producers generally render out all tracks in a project as a collection of ‘stems’, which is essentially all tracks printed down to uniform audio files. These stems are then imported into a brand new mix session, ready for the final mix. This multitrack mix session comprises dozens – or even hundreds – of individual tracks, which can all be levelled, panned and processed on the journey towards a well-balanced, clear, punchy mix.

Once the mix is complete, it’s bounced down to a stereo file (the ‘premaster’) and sent to a dedicated mastering engineer, who takes that single post-mixdown stereo file and applies a final stage of processing. At this stage, the goal is to fix any errors missed at the mixing stage, and ultimately optimise it for commercial release.

As you can imagine, working with a single stereo file is somewhat restrictive for the mastering engineer. Any EQ adjustments to the premaster will affect all instruments uniformly, and dynamics processing (compression or limiting, say) will react to the entire balance of signals within the mix. What if the lead vocal is a little too loud? Then it’s time to go back to the mix engineer and request a readdressed version. Yes, multiband processors can be used to isolate and affect specific frequency bands, but the introduction of crossover points and their phase relationships often cause problems of their own.

This brings us to the relatively new field of stem mastering. The term is somewhat of a buzzword at the minute, but there’s quite a bit of confusion. Essentially, instead of rendering out the final mix to one stereo file, the mix engineer instead exports a collection of five or six stems – say, vocals, kick, bass, drums, guitars and music – and send those to the mastering engineer, who can then throw these stems into his or her session and master the song with an extra stage of control and detail.

Many mastering engineers don’t offer a stem mastering service, and still prefer to work with one stereo file. And due to the additional work involved, those professionals who do offer stem mastering may charge more money for the privilege. However, if you like to mix your own tracks, and you’re not 100% confident that your mixdown is up to scratch, stem mastering could be a suitable middle ground.

Alternatively, if you want to master your own songs, this method may be a good way of keeping a healthy distance from the mixing process while still letting you make the final adjustments needed. Plus, as a bonus, you’ll have a condensed set of stems that can be neatly archived away for storage, and even future remix projects.