This is just a side-note on this topic. There are often times when I download a spoken word podcast and the audio is low. I find that it works well to use the volume normalizer audio filter built into mplayer. This will automatically equalize the audio and make the very soft parts a bit louder.

Simply add the following parameters like so:
mplayer -af volnorm my_podcast.mp3

I personally would avoid putting this into a config file, because it can sometimes cause music to distort, especially during a sudden change to higher levels within the music.

Take care