WaveGain is an application of the ReplayGain algorithms to standard PCM wave files. Calculated gain adjustments are applied directly to the audio data, instead of just writing metadata as traditionally done for other formats like MP3, FLAC and Ogg Vorbis. The replaygain values can also be added as metadata in a custom RIFF chunk named ‘gain’. This could theoretically allow WAV files to have same lossless functionality as other formats where audio data is not altered. But since no current players are aware of this “standard”, the metadata is used only by WaveGain for the “–undo-gain” feature, which is lossy.

github.com/MestreLion/wavegain