I just wanted to mention the free utility normalize that normalizes WAV files so your music will all play at the same volume. This really removes the need to keep adjusting the volume between different albums.
To install normalize, first download the source code. Next, navigate to the source directory, and type (you'll need the Dev Tools to do this step):
% ./configureIf you have fink and audiofile installed, you can install normalize with this option to be able to normalize AIFF files and other formats as well:
% make
% sudo make install
% ./configure --with-audiofileTo use normalize, just type "normalize" followed by the locations of the WAV files to convert as parameters (drag and drop helps). This process is very quick, taking only a few seconds. For example:
% make
% sudo make install
% normalize /Users/jsmith/a.wav /Users/jsmith/b.wavNote: The WAV files will be overwritten in the normalization process.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020626011549376