https://www.izotope.com/en/learn/mastering-for-streaming-platforms.html
Most leading streaming services have implemented some form of loudness normalization, turning the act of mastering for streaming platforms into a bit of a minefield.
In this article we’ll take a look at some myths surrounding how the different services normalize audio, whether there are ideal LUFS and peak levels, how normalization impacts song-to-song level balances in albums, and why some songs still sound quieter than others, even with normalization turned on.