Go to Edit > Preferences > Player . Enable Equalise volume using ReplayGain tags .
Every individual song is normalized to the same target loudness. This is perfect for custom playlists, shuffling, or mix-tapes. However, it can ruin intentional artistic choices—such as a quiet intro track on a concept album sounding just as loud as the heavy tracks that follow. flac gain fix
If you prefer using scripts or work on Linux/macOS (or in WSL on Windows), metaflac is the powerful tool that comes with the official FLAC package. Go to Edit > Preferences > Player