Many older CD's (especially those from the 1980's) have pre-emphasis on them. Pre-emphasis is when the frequencies of the original recording are modified according to a pre-set EQ template before transferring the music onto a CD. It was done to address some distortion issues. CD players were designed to detect this and then "de-emphasize" the CD so that it sounds as intended. There is a small file placed on the CD in the header area that flags the CD as pre-emphasized. But most multi-media players do not detect pre-emphasis nor correct it. A pre-emphasized CD sounds like absolute crap to put it mildly. One such CD that has pre-emphais that I ran across recently is Heart's self-titled 1985 album. The original pressings if not de-emphasized, it sounds like someone went nuts with the treble settings & took out all the mids. Modern recording techniques / transfers do not require this.
Any chance of adding pre-emphasis detection and have MB de-emphasize the tracks? The affected files would have to have a custom tag added by the user (I.E. "PRE_EMPHASIS" with a value in the tag such as 1 or yes) for MB to detect it. I only know of one multi-media player that has a plug-in for this at the moment (foobar).
If the capability was added to MB, it would need to be done in a pre-process way. That way you can take the pre-emphasized tracks, convert them and they will be permenantly de-emphasized. If it is a dsp type effect, it will not work as that is post-process. I have done this with a few CD's via foobar.
If MusicBee could detect the pre-emphsis flag on a CD (and apply de-emphasis pre-process), the plugin/tag method would not be needed when rippiing from a CD. But the issue comes when you have tracks already ripped that are not de-emphazied. Then you need the tag method, because the flag may not have been included in the track data.