MP3Gain Express is a program that helps you analyze and, eventually, increase or reduce the volume of MP3 files.
The application comes with an intuitive interface which allows you to understand easily how this tool works. Once the files are brought to the conversion file list, you have the ability to analyze the volume and to delete the tracks to which you don’t want to apply Gain anymore. If you consider that the volume increases or decreases more than you want, the program allows you to change its parameters (the volume is shown in decibels). The volume optimal for your health is 89.0 dB and I recommend you to leave it at this level. Once you have completed the list of files to which you are going to equalize the volume, you just press ‘Apply Gain’ and the process starts.
Since the process is irreversible and it doesn't create any temporal files, I personally advise you to backup your personal files in case you are not satisfied with the result.
The program is designed for those having lots of MP3 files taken from different media or websites and want to equalize the files to a standard volume.
In general, I was satisfied with the result. I tested it on 30 files, but in 6 cases I received error messages. However, the process didn't stopped; it applied the volume modification on all the files, excluding the ones with problems. Except for this issue, I believe that the program is worth trying because it is good and, of course, because it's free.