Vloud is a simple web tool that you can use to increase the loudness of your MP3s. If you think that your Mp3 is not loud enough for you after adjusting the volume to the max, you can use Vloud to make the adjustment.
vloud is a free audio tool upload quiet mp3s, and get louder ones back
Just select the level of loudness you want and upload your Mp3 then download it back in its louder form. The intensity of the loudness upscale is not mentioned in the website. It just lets you pick the level by yourself. There is no added information whatsoever. The only way to find out is to test it yourself.
You can upload mp3 and wav files and make them louder. Each upload is allowed a 10MB file size limit which is good for high bitrate music files. I only did one test and it worked great. I didn’t get to test if it will allow you to reduce the volume of loud mp3s. Anyway, this might come in handy from time to time.