advice on "pre-mastering"?

im thinking of getting a few of my tracks professionally mastered. It wont be released or anything, but ive always been curious as to how much difference it would make.

Ive heard to not compress the entire mix in any shape, way, or form as this is irreversible in the mastering stage. Okay, i understand that, but how about things like the drums?

Is it still possible to compress each track with its own compressor inserted into the channel with different tweakings? Will this be considered too much compression prior to the mastering stage?

Or should i be leaving the entire song left untouched with EQ/Compression and just send in the dry format to the engineers?

One of my main concerns, is that i tend to compress my drums HEAVILY and sometimes even overcompress on purpose to create that breathing/pumping effect. I tend to really compress the shit out of the hihats on its own channel, then send all the drums into a master FX channel where it all gets compressed together.

Im scared after all this compression, if i send the track in to get mastered and compressed again by the engineer, the entire mix will sound squashed.

Any ideas on what to do, and what NOT to do when your track is ready to be mastered?

If your using compressors on drums for a certain effect, then this is fine. You wont get the pump back by mastering. As long as you dont compress the main mix and limit it, then they should be able to do it. Dont forget, the compression used in mastering should have no effect on the feel of the track, so make sure you have it pumping before you send it out..

AS Al says above, dont limit the track, ideally you need to be looking at about 14db or there abouts of dynamic range before the piece goes to the mastering house.

Al makes another good point which is that the compression will be as transparent as possible, they are masters not makers.

Most of the things you describe are to do with the mixdown stage of the production not mastering, so go ahead, knock yourself out with comrpessors on every channel if you so desire.