How do certain artists get a whole track uploaded onto their myspace and have it sound near to crystal clear?

I have gone on many artists sites especially known ones like madonna and their tracks always seem to sound crystal clear. I have a mixed down track ready to put on myself what can I do to this file before I upload it to myself t keep it sounding as clear as possible?How do certain artists get a whole track uploaded onto their myspace and have it sound near to crystal clear?
myspace only hosts the file,... it does not 'in theiory' effect the sound quality of the song...





if the song is of good quality to begin with,.. then you should be able to upload it, and have it keep its quality