Is there a technique for preparing a recording for Mp3?
Could you elaborate on how you make an MP3? Are you rendering directly to MP3 from a DAW or are you mixing down to a .wav file and then encoding that? What tools do you use?
A way that works for me is to render down to a high quality 24 bit 48Khz wav file from DAQ, open in Audacity, normalise, and use the high quality LAME encoder settings. See http://www.audacityteam.org/