A modern mp3gain / aacgain replacement written in Rust. A native GUI application (mp3rgui) is available for users who prefer a graphical interface.

mp3rgain adjusts MP3 and AAC volume without re-encoding by modifying the global_gain field in each frame. This preserves audio quality while achieving permanent volume changes.

github.com/M-Igashi/mp3rgain
crates.io/crates/mp3rgain
hydrogenaudio.org/index.php/topic,129648.0

References:

github.com/dgilman/aacgain
mp3gain.sourceforge.net