you may realized sometimes that your songs have a different volume.
this can be easily fixed by using
MP3Gain
you can choose whole folders... mp3 gain will pick out every mp3 file.
then you can equal them all with one klick:
"constantly adjustment" let you select an +/- amount, to adjust the volume manually because sometimes normal adjustment does not work properly. (eg in case the mp3 file is corrupt)
these files will be highlighted red.
A big pro is that this program is rly FAST!!
btw: you can also use to increase the volume at all to make them sound louder on your mp3-player.
but beware: prolonged listening at high volume may damage your hearing...