How the boost works
This tool applies FFmpeg's volume filter, which multiplies every sample in the file by the same factor, set by the gain you choose in decibels. A decibel is a ratio rather than a fixed step: roughly every 6 dB doubles how loud the signal reads, so +6 dB sounds about twice as loud as the source, and +12 dB sounds roughly four times as loud. Because the whole file is scaled evenly, the balance between quiet and loud parts of the track does not change, only the overall level does.
The catch is that scaling everything up also scales up the loudest peaks, and once a peak goes past full scale it clips into a harsh, crackling distortion. The Prevent Clipping option, on automatically whenever you boost, runs an alimiter after the gain stage that gently holds back only those peaks, so the file gets louder without the crackle, in exchange for a small amount of dynamic range.