What are MP3s?
Mp3 is a called Mp3 because it is essentially in the MPEG format in the third layer which means that it is a highly compressed file and it can be compressed without losing much quality.
In English:
MP3s are files that don't take up much
space on your hard disk but sound a lot like cds. Oh, and they're free most the time.
Even More Technically:
MP3s are masked in that only the audiable tones of the sound are written.
Subsonic and ultrasonic noises are disposed of because they do nothing but hog
space; you can't hear them at all. This might make MP3 music less enjoyable to
your dog, but otherwise will not effect your listening experience in any way.