Like the word "Boat" is pretty easy to line up, but "Stack" isn't so much. Do you line it up with the start of the 'sss' sound, or the 'tttt' or the vowel?
I dunno... IMO, I think you might be being a bit too picky about this... how many "S's or 'T's" are you adding to the word? I mean, unless you're
really dragging out syllabic consonants, I really don't know anyone who sweats that much over whether or not the "S" in Stack or the "T" in Stack lines up
precisely with the downbeat, unless you are really stretching those "S's" out beforehand. I suppose it depends on tempo and style, and, when you are comping, how late - or early - are the comped vox in respect to the beat? Are we talking being off off by 1/16ths, 1/8's, full 1/4 note beats? Or off by something much smaller, like ticks or frames?
You could engage a metronome during playback and do it by ear, or, you can find the start of the beat/measure visually by looking at either the measure/beat markers on your timeline editor, or, you can also use one of your existing transient tracks (like kick drum, hi hat,etc) as a visual cue and line them up that way as well.
There are also some DAW's which have an audio quantize feature, which allows the user to define a certain resolution, at which point, just like midi, the vocals are automatically lined up to a beat, but, you can also get some pretty weird artifacts doing it that way, because in order for it to work, sometimes words, syllables, consonants, etc., can be sped up, slowed down, or, even chopped off. The quantize command is looking for the easiest way to shift all those parts so that they reflect a particular note or tick/frame resolution that is set by you.
Depending on the style, it can be important to have good timing and have a word/phrase start at the same time as the down, but doing that
all the time can also make things pretty stiff and robotic too.
I'd be more concerned with making sure that the phrasing
as a whole sits well within an entire section, and/or, if you have multiple vocals happening that all sing the same parts - like doubled lead vocals or backing vocals - that they all
end at the same time, particularly with words that end in S, T, CH and K (or hard C) and Z (
or "zed" for our Canadian members LOL).
Often, relaxed vocals, with phrasing that isn't
precisely in line to the beat, can add more feeling and vibe to a track, as opposed to everything
always lining up
exactly with a beat all the time...
IMHO of course.