mp3gain (adjusts mp3 files so they have the same volume)

MP3Gain does not just do peak normalization, as many normalizers
do. Instead, it does some statistical analysis to determine how loud
the file actually sounds to the human ear.  Also, the changes MP3Gain
makes are completely lossless. There is no quality lost in the change
because the program adjusts the mp3 file directly, without decoding
and re-encoding.
