A simple but clear article on the topic appears on the What HiFi web site...
Here is a case in point... the new Beck album on HDTracks ... Oh dear, where is the honesty and transparency?
This article also provides many links to other pages including a topic I have raised before... "The Loudness Wars" http://en.wikipedia.org/wiki/Loudness_war . A layman's description of the process of remastering recordings which often seems to produce louder but not necessarily better CDs, MP3s etc may be read at http://entertainment.howstuffworks.com/remaster-cds-dvds.htm
Here is another comparison of cheap vs expensive HDMI cables... guess what?
The question as to whether mains cables can block out RFI from domestic Audio equipment is discussed in the following article http://www.audiomisc.co.uk/cables/mains/StringTheory.html
To be continued....