If music is recorded too loud, its sound is altered. Then, it sounds distorted, similar to what you probably know from an electric guitar. To still be able to use high volumes, a so-called compressor is used in the recording studio.

Try it out and see how it works! Move the left slider down. The loud parts will now become quieter. Since the overall volume of the music now fluctuates less, you can amplify it with the right slider without causing distortion. The overall sound becomes louder this way, but it may result in an unnatural quality to the music.