"One issue that you run into quite a bit in mastering is sibilance on the vocal.
Getting the top end to shine without being abrasive is where I think frequency selective compression can help the most in the mix phase. You can use a couple bands of ambcora simple de-esser or 2 set in notch or shelf mode to help if the S's, Ch's, T's, K's, F's are a problem.
To identify and dial in the problem frequencies or sibilance on a mb you can use the solo mode of a mbc or the listen mode of a de-esser. A frequency analyzer can also help identify and pinpoint the problem frequency when you hear the sibilance and then see where the frequency jumps on the waveform. Automating the threshold of a de-esser to only re-act in the area needed can also be helpful and keep things more transparent.
The attack times on that kind of stuff (sibilance) has to be pretty quick because it's on the leading edge of the signal. Release can be quick to medium as well as you want to retain a natural phrasing without cutting into stuff that's not a problem.
Plosives are another issue to keep an ear out for, but that happens in the low register (usually 180 Hz and below) and can usually be zapped with a spot Eq (high pass filter) on an area that you can identify with a place on the waveform that's caused by a burst of air into the mic happening right before the P or B sound.
Most other issues for general frequency shaping on the lead or backing vocals can usually be taken care of with a static eq (if needed) and a bit of broadband compression, but less head aches in the mixing or mastering stage mostly start with a decent mic, a widescreen, good vocal technique and attention to detail in the tracking phase.
- once the frequency is pinpointed,..2 to 4 dB of gain reduction showing on the gain reduction meter for the worst offenders should be enough, so the consonants still sound natural. One characteristic for telling if you've gone to far is the voice will sound like it has a slight lisp. If that happens you can back off the threshold and confirm that you are nailing the right frequency"