There is noticeable distortion when my mastered MP3 are played through iTunes. There is no distortion when it is played outside of iTunes and on other systems. I am mastering to -12db more or less. The only time there is no distortion in iTunes is when I master to -23 LUFS. There is no transient peak above 0db. Why is there distortion? I
I also noticed that reference material and other tracks in my iTunes library do not have distortion. One track in particular has no distortion but is metering at -10 db with transients of 1.3 db yet it plays mostly fine. It is a great mystery to me. Perhaps there is a simple answer?