MP3Gain is a tiny but brilliant tool for fixing inconsistent MP3 volume levels. Instead of simple peak normalisation, it analyses perceived loudness and adjusts files losslessly — no re‑encoding, no quality loss.

Why it’s great:

🔊 Real loudness analysis (not just peaks)

🛡️ Completely lossless — changes are reversible

🧩 Works on batches of files

🖥️ Cross‑platform options exist (Windows GUI, Linux GUI, Java GUI)

🎶 Supports AAC via AACGain (with some caveats)

Still one of the most reliable tools for taming messy music libraries despite its age. (tested on Windows 11)

Note:
Mp3gain requires Microsoft Visual Basic run-time files on Windows, which you may not have installed. Use the download version which includes the runtime files.