Mixing for a STEMS-master?
Particular care should be taken when preparing a mix for STEMS mastering. The entire mix should be planned as a STEMS project from the start to avoid the harmful ways that the gain-structure can interact with master-bus processors.
If you sub-mix elements like Drums, Bass, Guitars, Keys and vocals into stems, and then mix them through stereo-buss processors like a compressor, for example, the bus compressor will affect the whole mix proportionately to the signal at the compressor inputs, while, when soloing the stem individually, the compressor will behave completely differently to when the entire mix is going through it. So, if you bounce stems individually through a common bus compressor, then, when you re-combine the stems and compare it to the mix on the board, they won’t sound the same as when the whole mix is playing through the compressor on the stereo bus.
If you’ve planned the mix well from the start and can implement the stems mix without anything on the stereo bus, then stems can yield very good results for mastering.
Bottom line: If your mixing for a stems master – DON’T use stereo bus processing! Or, make sure you’re doing it deliberately.