MP3Gain
Have you ever had problems with mp3 audio levels? Many times I have burned a CD to play in my car only to find out that it just didn’t sound loud enough. It sounded great on my computer with software to automatically equalize it, but it was just too quiet through my car’s system. This was a problem for me until I learned about MP3Gain.

“MP3Gain analyzes mp3 files to determine how loud they sound to the human ear. It can then adjust the mp3 files so that they all have the same loudness without any quality loss. This way, you don’t have to keep reaching for the volume dial on your mp3 player every time it switches to a new song.” ~MP3Gain Help
You can see from the above picture that I ran the track analysis on my Van Morrison Moondance album. You will notice that most of the songs are around 90.5dB, but the third track is 85.9dB (about a 5dB difference). There are two things I can now do depending on my preferences.
1 – I can press the track gain button and this will change all the tracks to whatever target volume I desire, in this case 98dB.
2 – I can press the album gain button and this will keep the volume variance of the album in tact while increasing the desired overall volume. This would make most of the tracks around 98dB, but the third track would be 93dB (keeping the 5dB difference in tact).
Visit the MP3Gain website: MP3Gain