[LAU] keeping same perceived level on mp3 files

Hi I play keyboards in a couple of bands. When setting up my sounds I often find that on some songs my keyboard is much louder than on others. I'm pretty sure it's because to the extremely mixed level of the mp3 files I use for rehearsing and programming the synth sounds. So my question is: how can I match the levels of the mp3 files so that they will playback in levels "as close as possible to the level a my band plays them"? I imagine a ballad would be played back at lower level than a power rock tune, not sure if there's a way to compensate for that, though. So at least something that sounds like the same level. NB: The tunes vary a great deal in audio quality and loudness-war-compression (some are new dance/pop tunes, some are old soul tunes, some are something else). Thanks in advance for any input! -- Atte http://atte.dk http://modlys.dk