MP3Gain analyzes and adjusts mp3 files so that
they have the same volume. It 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.