This mp3/portable earphone music player gransition may have a similar impact to the change from vynal to CD. As vynal physically couldn’t allow alot of bottom end due to the cutting of the actual physical waveform into the vynal, that effected how mix engineers approached things. I’m not sure if it is due to my largely earphone based listening experience, or my love of 1990 albums like Nirvana’s nevermind and Radiohead’s ok computer, but I do think modern music is becoming bass heavy, often to a negative effect.
p.s. apolagies for the long comment, its my first time coming across this site, I love it, and I had alot to say on this subject!

http://www.avisoft.com/compression.htm

Lossy compression algorithms vary across the board, but they all function primarily by attempting to reduce file size by reducing the fidelity or removing altogether parts of the audio spectrum deemed unnoticeable to the human ear. For example, this is sometimes accomplished by decreasing bit-depth at ultra high frequencies or frequencies that are masked by big sounds. Reducing bit depth can contribute to distortions and unwanted harmonics as waveforms become more step-wise in their formation.

Aside from that, we all know, the human ear can “perceive” much more than it can “hear” so even the best lossy compression has some tangible effect on sonic quality and therefore is built on a faulty premise.

The real question becomes whether or not that change in sonic quality is enough to damn the compression algorithm altogether. The increasing trajectory of .mp3 files toward becoming the standard format would indicate that the loss of fidelity is not significant to the market on the whole.

Similarly, distortions in spectral content are not always a bad thing. The aural exciter is an example of people adding selective harmonic distortion and enjoying the consequences in so-called professional “hi-fi” audio circumstances. The problem with lossy data compression algorithms is that the spurious harmonic additions tend to be random and therefore the outcomes are unpredictable; whereas the aural exciter has a fairly uniform end result.