The correct term is mastering from stems : The stems themselves don’t get mastered; the stems form part of the master.
This has become somewhat of a speciality at Stardelta. We do a lot of this. Put quite simply, the degree of control available when a group of stems from a mix are provided for mastering enables results not possible with a stereo mix. The results are always superior to mastering from a stereo mix and for good reasons. Splitting the mix into a group of perhaps 7 (example below) stems gives so many more possibilities in terms of fine-tuning the sound and it allows adjustments to be made that really enhance both the sonic and technical characteristics. Technically, mix errors can be dealt with more easily and with less interference with other elements in the mix leading to less if any compromise on eq decisions. Sonically, more individual colour and flavour can be injected into the mix, targeting the stems that need certain treatments as well as the master as a whole.
How does it work?
How do you supply what we need to get the best results from stem mastering?
It works by splitting your mix into separate sub groups of stems. For example:
1) Kick Drum
3) Drums (midrange)
4) Drums (High Freq)
5) Musical Parts 1 (group of musical sounds and FX)
6) Musical Parts 2 (Group of musical Sounds and FX)
You should supply these stems exactly as they are intended to be in your mix. This means all grouped stems when played back together should create your mix exactly as you intend it to be. All Effects used during your mix should be printed into these stems in order to reproduce your mix in full.
You should open a new session and import and check these stems against a stereo mix you have already made. There should be no difference. If they are drastically different and not at all correct you must start again and determine why they are incorrect. (Bounce settings and wrongly routed track and FX settings are the usual culprits) The stems, playing together, should sound identical to the stereo mix you made before grouping the stems. If they do then they should be sent in one folder for each song and form the premaster source for a stem mastering session.
Stem mastering is not mixing.
You will need to have mixed your track and be happy with that mix as far as is possible- just as happy as you would with any mix you send in for mastering. You should be sending that mix you are happy with but broken down into stems. If there are subtle changes that need to be made to balance the level of these stems as part of mastering, this is accepted to be part of the process but the balance will ideally remain as it is in your mix, but be greatly enriched and improved. The idea of stem mastering is not to change your intended mix balance but to enhance and to improve or to modify and correct any technical issues in more detail.
As per a normal stereo master try and keep peaks on the main mix bus between -10 to -4dBfs (Digital Full Scale) but no higher than -3 dBfs. If they are higher we would recommend lowering the individual mix element faders and group faders to reduce the level on the master output bus. You need to leave the master fader at 0 and work the faders and groups within the session (if Mixing in the box)
Please see standard premastering advice for more specific info on stem mastering and preparing stems for master.
Please contact us if you require a full mixdown. This can be arranged either ITB or on a console with outboard using 24 track analog tape if required. POA.