If you are unsure how different elements of your mix are sitting, then we encourage the provision of stems for your mastering session with us. This is a service we offer at no extra charge.
Stem Mastering is the use of separate mixed down elements of your song which we will process independently and combine together during the mastering session. So, instead of providing just the stereo mix as normal, you could [for example] provide us with the drum mix, vocal mix and instrument mix separately for us to evaluate and place more accurately.
It allows us to not only get the levels absolutely correct, but also gives a little more room for creative expression. For example, we are able to process the vocal stem with a different approach and different equipment to that of the drum or rhythm stems.
It's as easy as bussing each collection of elements to a group before it hits the mix bus... drop us a line if you'd like a more detailed explanation of how to do this with your specific DAW [digital audio workstation].