The quality of digital files downloaded online can sometimes be dubious at best.  What sucks is that some of these music sources do not give you any idea of what the quality of a song will be before you download.  Some of them just say things like ‘CD Quality” or a 320kb bitrate.  They don’t tell you the things you want to know, like what CD quality music actually stands for, or if your bitrate is constant or variable.  Some of the top music providers like Amazon, Apple, and Beatport are all guilt of having poor quality music from time to time, and some of that is not their fault or responsibility. For most of us who were downloading music before it was as popular as it is today, we have a collection of songs with varying degrees of quality.  Some of them sound like they were recorded from a cassette player on a CD, and some of them have terrible quality for other reasons – like human error.  While it would be nice to repurchase all of these songs in perfect working order, it is not always possible and the only alternative is to actually go into each song and adjust them accordingly. http://www.djtechtools.com/2013/07/16/review-mixed-in-key-platinum-notes-4/