This is off the top of my head, but a fitting addendum to Morph's dilemma- The reason why a lot of people cannot tell the difference between 320kb mp3's and uncompressed has a lot to do with the output Digital to analog converter they're using. The cheap ones, sigma delta, as they are named, act like switching power supplies to make audio signals.(hence, how you can get 16 bits of resolution out of a 1 bit DAC) But in order to keep the switching speed out of the gigahertz range, the cheap DAC's are pro-rated to what the average ear can hear. So, audio information is dedicated exponentially from the low end up. As you hit the 20 khz ceiling, the cheap DACs reproduce these higher frequencies less faithfully. Ergo,the highest quality MP3 will show it's limitations on a high quality DAC, made of resistors, versus the uncompressed file, but cheap DACs will stifle uncompressed audio.