Mastering From Stems
The main reason mastering is considered to be such an art is because it can significantly enhance a track without direct access to its individual mix elements. A mastering engineer listens and thinks holistically and any move they make has an equal impact on every sound within the affected frequency range - so adjustments must be subtle and precisely targeted.
Stem mastering breaks that paradigm, but in some cases where there are slight issues in the mix, it can be the simplest and quickest route to a great sounding master, by enabling the mastering engineer to make changes to specific groups of sounds independently of the rest. This can be particularly helpful for artists and producers who prefer to do their own mixes, but are nevertheless not totally confident in the end result especially in terms of overall weight, impact, clarity and so on.
Even with this added control, the goal remains the same - which is not to change the mix but to present it to the listener in a way that best reflects the intentions of the producer.
We usually charge for attended stem mastering by the hour at the same rate as for straight stereo, but it can take longer so bear that in mind when you book. We can discuss fixed rates with you upon review of the material, or apply our online rates for unattended stem work with the addition of £10 (+vat) per stem supplied. Some folks will bring stems along to a standard mastering session as a fall-back position, and that’s also fine, provided you’ve allowed for the additional time.
Before we go into more detail, one important caveat is that stem mastering is not a substitute for a strong mix. If the mix just isn’t working then stem mastering won’t fix it, and if the mastering engineer has too many issues to address and ends up having to think like a mix engineer, they’re no longer doing the job you’ve hired them for.
The Principle
Firstly let’s imagine the ideal scenario: a well-balanced stereo mix. It has headroom, a full frequency range, low noise, and a carefully blended arrangement. The mastering engineer’s task is to smooth out small issues, apply gentle compression or EQ if needed, and make sure it translates well in the real world, sounding just as good as it did to you when you laid it down.
In our ideal-world example this is of course no problem at all. Let’s say it would benefit from being brighter: your mastering engineer reaches for their sweetest sounding EQ and adds some top, and consequently the cymbals have more sizzle, the snare has more snap, the vocals have more air, the guitars more presence and the keyboards have more sparkle. Everything sounds better – a win!
That’s the ideal scenario, and frequently mastering sessions go more or less along those lines. However there may be aspects of your mix that you’re less sure of; for instance, what if you want to brighten up the vox and guitars but the cymbals are too bright already? You could go back to the mix studio for a recall, but if you’re struggling to find the perfect balance it could be simpler to just EQ those elements separately at the mastering stage.
Tweaking the bass and drums independently of the rest of the arrangement can be very useful when mastering, especially given that the bottom end of a mix can be very tricky to get right in a project studio environment where the monitoring isn’t necessarily very accurate. The ability to EQ the bass instrument and bass drum individually in the mastering studio can solve all sorts of previously unseen problems and help you arrive at a wonderfully tight, deep and punchy bottom-end.
What Is A Stem?
A stem is a component of the mix, rather than simply an edited recording of an instrument. Together, all the stems should reassemble into your full mix, identical in timing and level to your stereo version. They should all start at the same point and include relevant effects unless you’re supplying those in separate return stems.
How many stems you provide is up to you. The simplest approach might be two – vocals and backing track – avoiding multiple alt mixes like “vocal up” or “vocal down.” A common four-stem layout for pop or rock would be: vocals, drums, bass, and everything else – or, put another way: top-line, percussion, low end, and harmony. A simple layout like that will often provide enough scope to address a range of common issues.
At the other extreme you might have a different stem for every instrument. This is more common in situations where the producer or mix engineer is viewing the stems more as an emergency or backup option - making future remixes possible even if the current software no longer works. In this scenario you have total control over the balance of instruments in the mix, but retain the EQ and other effects used in the mix studio. However, such large numbers of stems are generally not advisable in a mastering scenario.
Mixing Stems: Some Guidance
There are a few things to consider when planning your stems. As a general rule it’s always best to keep things as simple as possible, so think about what you want from your stems and only create as many as you need; grouping instruments together where you’re confident in the balance and only separating those elements you’re unsure of.
If you’re mixing outside the box through an analogue desk, consider noise. If any of your effects returns are noisy for instance, mute any returns that are not being used for a given stem. Remember that when you re-combine the stems at the mastering stage, any noise will be compounded as you add each stem to the mix. For this reason alone it’s worth aiming to use as few stems as necessary.
Bus compression is another factor. If your favourite comp is doing its thing on the mix bus, it will respond differently as channels are muted to create stems – meaning your stem mix won’t sound like your stereo mix. If the compression is essential to the sound, you can still provide stems by side-chaining the compressor from the full mix, so its behaviour remains consistent.
Lastly it’s worth bearing in mind the danger of deferring decisions. You should be happy with your mix before you book a mastering session, even if you are intending to work from stems. There is such a thing as too much control, and the mastering studio is not really the best place to be endlessly debating the level of the third cabasa overdub, or deciding to pitch-correct the melodica…
As always if you have any questions, technical or otherwise, our engineers are here to help so just give us a call on (0)20 8743 8585 and ask for Nick or Tim