And so, MP3 magically minimizes the loss of quality by shaping the compression errors in a clever manner, and this is done in something that is called the Short Time Fourier Transform domain, which we don't explain now in detail, but the idea is essentially a DFT that is local, so, over small pieces of music, you take a Discrete Fourier Transform, you look at the spectrum of the music, and you put the noise exactly where it's not going to be heard. 