GAB - nakedzen:
I usually sculpt the kick and bass gtr to compliment each other. Cut 120Hz from bass and 80 Hz from kick or vice versa, however works best. Cut some low mids if it's too muddy. Boost 750Hz or 1.5kHz (whichever works best) to make the bass present through small speakers. Low pass usually at 8kHz, maybe even as low as 2kHz depending on the mix.
Use a compressor, with at least 4dB of gain reduction. I really like Variety of Sounds Density MkIII for bass.
What I usually do with the Density (I'm not too good at tweaking comps either

) is load one of the presets, the "Larger than life" being my favorite, tweak the amount of gain reduction to where I want it or where it sounds best, raise the volume back up with the Makeup knob and that's it. I usually check that it's the same volume with the comp on and off and adjust the makeup if it's not.
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GAB - PamukParty:
Depending upon what I'm doing (putting together small clips vs. full song mixes) I do different stuff. I always use a built in preset sim in Amplitube just to get a decent tracking tone - then promptly pull it off the direct track once I'm done.
For small/quick clips:
Off the direct track I split out 3 parts (one is raw direct and I eq it so that it's just the low part of the bass, the second track is usually with an amp sim but is aggressively low/hi passed just for some character, then the third is another amp sim / pedal combo that is just for distortion (again heavy low/hi passed).
The low part track I then sculpt around the bass drum (edit - boost the bass around 80hz, cut around 60hz but this is kick dependent), hi/low pass, and carve out the 400hz range to clear out mud that can build up
hi pass usually on this track is around 40hz, low pass is between 300-500hz.
For the bass amp track the hi pass is usually around 500hz, and the low pass is around 5000hz
The distortion track hi pass is usually 500-750hz and the low pass is 5000-6000hz
All three tracks are then fed to a single bus where I compress pretty heavily. I shoot for 5-6 db reduction.
From a mix perspective I use the bus fader to adjust the overall level of the bass, then the three faders depending upon what the mix is doing. Need more lows then up the direct bass track. Need some more punch - up the bass amp track, etc.
For quick mixes this process usually does a passable job - although solo I usually don't like the tone very much.
Here's an example of one I'm currently working on using the quick method -
No Guitars
http://www.tonefinder.com/index.php?sec ... alue=14920Guitars Added in (all Amplitube - scratch tracks, dont' mind the tone/playing)
http://www.tonefinder.com/index.php?sec ... alue=14922For full on mixes the principles are the same except I process waaaay more. Multiple compressors, Limiters, more nutty eq. I also will mic up a guitar amp to get the grit part and bass amp on occasion as well.