If you know what to listen for in the high frequencies, you can pick out mp3's pretty easily, provided said mp3's have that sort of content. The question reall

If you know what to listen for in the high frequencies, you can pick out mp3's pretty easily, provided said mp3's have that sort of content. The question really isn't 'can you tell', it's 'does it matter', and, well, most of the time, no, it does not, even for lower bitrate mp3's. There are many people, of course, that don't like the idea of lower quality audio, and they can tell at least sometimes, so they 'dislike' mp3 in general. That's all well and good until they start saying silly things like 'mp3's sound bad', which is not true in any sense.