Some speculation on the preference for loudness: I almost posted something on this previously, but decided not to. I suspect that the "loud is better" actually comes from a desire for denser spectra and that strategies for providing denser spectra have been thwarted by some people simply increasing the volume. Increasing the volume can produce the illusion of a denser spectrum be increasing the amplitude of some frequencies so that they can be heard, or it may simply cause more things in the room to rattle. But once you set the volume for the louder songs, those that actually have denser spectra may sound as though they don't because many frequencies fall below the threshold and/or don't rattle anything. They sound thin again. So people creating dense spectra ALSO need to increase the volume to keep up with the volume settings, sad to say. There may also be a psychoacoustic effect that louder produces more harmonics or an illusion of such. Two trends in the history of pop music that seem to support this denser spectra idea are 1) Electric guitars; 2) Wall of sound. Occasionally people back off from these, but the pop charts are full of songs with dense spectra. I don't know about others, but every time I hear a female solo voice, I am expecting to hear it followed by something with a dense spectrum such as power chords. There are those who, of course, do not like this and prefer purer tones, but even these people often prefer richer tones that have lots of harmonics, such as organs, over simple sinusoids. If you look at the development of any particular genre, you can also see (hear) an increasing spectral density. Often this is accomplished by simply adding more instruments.
