FFmpeg is the gold standard for multimedia processing. It is completely free and open-source. You can normalize volume using the loudnorm filter (EBU R128 standard).
Unlike standard audio editors that simply amplify a track (which often leads to clipping and distortion), Mp4Gain uses technology. It analyzes the perceived loudness of audio tracks (in MP4, AAC, MP3, and other formats) and adjusts their volume so they play back at a consistent level, without altering the original audio files permanently unless specified. Mp4Gain serial
Some free software alternatives offer similar functionality without requiring a serial key. You might consider exploring these options if you're looking for a no-cost solution. FFmpeg is the gold standard for multimedia processing