When compressed MP3 Audio files were first used commercially, people would download from the likes of Napster and iTunes, websites that originally only provided 128 kbit/s files. Small files were initially the only option, as due to low internet speeds, MP3 download sites were not initially seen as a serious market, compared to high quality CD Audio. Additionally, in error, lots of unmastered source copy files were making their way online. This led to MP3s building up a poor reputation and spread concern that it was a poor-quality medium. However, it was not long before 160 kbit/s files were common, and then 192 kbit/s became the standard. As a mastering engineer I have done many blind listening evaluations, and from AB tests with the original digital source masters, it is difficult, or almost impossible to hear any difference between the original and 192 kbit/s MP3 files. Many sites like Amazon, now also provide 320 kbit/s files, which are more than perfect. Many people are seemingly scared of the word compression, incorrectly believing that it refers to dynamic audio compression. The MP3 encoding algorithms are amazing and give excellent transparent audio. At the end of the day, the single most important factor in audio quality are your headphones or speakers, as well as of course the space you are listening in; the acoustic properties of a room can make a substantial difference to sound. A great set of speakers poorly placed in the wrong acoustic setting can sound awful, and conversely a lesser set of speakers could sound superb in a room with the right acoustic.