[sciurius]

Normalising is a simple mathematical process that increases the overall level, such that the peak level is at whatever you have set it at (usually 0dB, or marginally less). If the original peak level was lower that this, then the track will, indeed, sound louder.

However, due to the way our ears work, the perceived volume of a track is actually related to the RMS average of the whole track and normalising does not change that average - it remains the same.

Quoting from the mp3gain documentation:

mp3gain does not just do peak normalization, as many normalizers do. Instead, it does some statistical analysis to determine how loud the file actually sounds to the human ear.

This seems to me exactly what is desired.