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well, first off like mentioned above if it is a dynamics problem then use compression. If you have a good constant level(constant meaning not destroying all of the dynamics that natuarally would be present in the song, however not exceeding db levels in the vox that make it sound too loud or too soft.) then I would suggest using a bit of eq and maybe some effects such as reverb/delay to smooth out the sound. If your vocals just aren't "riding" over the top of the mix and you want them too, try boosting 2 or 3 db around 15k-16k. If you prefer reduction techniques then reduce at a lower frequency... off the top of my head I can't think of what that relates to at 15k... sorry. Any way make you vox not overly wet, but enough that it gives the vox the characteristic of the effect you have inserted. And you know, it is very possible that you just haven't got the levels set well enough and you may just need to make your vox louder. If they don't sound clear first raise them up a bit and see what happens... But if they are blaring loud, then try something else...