Audacity
Since version 2.4.0 (May 2020), Audacity offers a Loudness normalisatin tool!
See release note.
Find the tool in the Effect menu > Loudness Normalizazion...
The legacy Normalize... tool is normalising based on sample peaks.
► The Loudness normalisation tool is recomended now. ◀
It event takes care of the Stereo VS Mono challenge.
Just keep Treat mono as dual-mono ticked and normalise at the recommended target.
