JP posted this in B-rad's forum
i wanted to add it down here in the hopes to help some people.
his technique is by far not a "trick", but something a lot of mixers overlook.
here is his post:
I'm no mastering engineer either, but as a mixer, i lowpass a LOT of tracks on a given mix. Many instruments, especially heavy guitars, can get nasty up above 10k or so. Aggressive vocals can sound better with the extreme top rolled off as well. Leaves room for other tracks that need extended top, such as airy vocals or drum OH's. That way, if so desired, the mastering engineer can boost a top shelf above 10k without worrying about bringing up nasty artifacts. Ditto on the low end as well, highpass anything that doesn't need to be down there with the kick and bass. It's all useless energy to me.