MP3Gain is free cross-platform audio normalizer software. It analyzes the MP3 and losslessly changes the volume. The volume can be adjusted for single files or as album where all files would have the same perceived volume. It is an implementation of Replay Gain.
MP3Gain analyzes and adjusts mp3 files so that they have the same volume. The program does not just do peak normalization, as many normalizers do, but instead attempts statistical analysis to determine how loud the file actually sounds to the human ear. The changes MP3Gain makes are completely loss less, there is no quality lost in the change because the program adjusts the mp3 file directly without decoding and re-encoding.
MP3Gain can modify files in two ways:
- write metadata
- modify MP3 data, writing undo information as metadata
In both cases, it first computes the desired gain , either per track or per album, using the Replay Gain algorithm.
In the first instance, it simply writes this as a tag (in APEv2, or ID3v2 format), which can be read by other applications that implement Replay Gain.
In the second instance, it modifies the overall volume (scale factor) in each MP3 frame, and writes undo information as a tag. Note that this is completely reversible. By subtracting the modification that was done and removing the tag, it does not introduce any digital generation loss because it does not decode and re-encode the file.