The overwhelming majority of the audio files I have are .mp3.

I don't even know if my ".mp3 player" can handle any other format; it has trouble with a few file formats for sure, so I convert the files just to be able to listen to them. This is usually a once-and-done deal for me. I honestly can't tell the difference other than "does it play?" and I have decent hearing. Maybe if I were some purist with perfect pitch I'd be throwing fits, but I'll leave that for other people. The audio is fine. I don't hear the problem.