Smart Gain is a commercial audio normalization tool. It can normalize the audio of a single file or several different files so that the volume of the audio tracks are similar. You may have experienced this problem before: some of your songs are considerably louder than others, so you constantly have to adjust the volume on your MP3 player. It is similar to what happens on TV when the commercials are extremely loud and the movie you are watching not loud enough. Smart Gain can automatically fix these problems. All you have to do is load the files onto the application by dragging them. You can add individual files or a complete playlist. After that, you can click on "Auto detect" and then on "Apply changes" to let the app carry out the normalization automatically. If you know about volume gain, you can do this manually by sliding a bar and setting the gain level manually. The supported volume adjustment is from -19.5 dB to 19.5 dB.
When there is a file loaded, the application will display in a time line all the volume spikes. You can zoom in and out of this line to see them in detail.
Smart Gain is a commercial app, but there is a fully functional trial version available.