MP3Gain automatically adjusts mp3s so that they all have the same volume.

PERMISSION  UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP     NAME
---------- ----------- ------- ------- ------ ---------- ------------ ----------
[generic]                 9651   26432  36.5% -lh5- 0bfe Sep 15  2008 lgpl.txt
[unknown]                70625  159252  44.3% -lh5- 7f6a Dec  7 22:07 mp3gain
[unknown]                 2045    4616  44.3% -lh5- 73ab Dec  8 11:44 faq
---------- ----------- ------- ------- ------ ---------- ------------ ----------
 Total         3 files   82321  190300  43.3%            Dec  8 21:02