Re: On air compression
Wanted to mention you can also add ReplayGain tags (both track and album) to FLAC files, the command-line app "metaflac" can do it. My player supports it, but YMMV.
The loudness issue used to drive me mad on my phone, but after much study I managed to patch the old Android (ICS) Music app to support ReplayGain on MP3s.
Only problem was when Jelly Bean came along and I recompiled the app, it now has "gapless playback" (i.e. a slight crossfade/segue) which when fading from a song with lots of gain applied to one with none or negative gain, there tends to be a split-second burst of EXTREME LOUDNESS until the equalizer adjusts it to where it should be for the next track. I must try to fix this at some point but I fear by then the AOSP app will be abandonware :(