by demigraff » December 2nd, 2013, 1:37 pm
As far as I can tell, it just means that the mp3's don't contain additional suggestion tracks that are pitch-shifted to be above the frequency range that your ears are capable of detecting.
(Note: If such an additional track was included, the audio compression process would strip it out. There's no point including audio frames that you can't hear, so your software will remove them to make the file smaller)