some additional thoughts about spectra:
as i know, the ear is a lot more sensible than the eye.
especially the ear is not only sensible to amplitude but also to phase of the signal and through this to stereophonic location of the source.
thus you may already hear artefacts and distortion long before you can see anything in the spectra. mostly the spectra are amplitude only and do not say anything about phase because its difficult to explain effects related to phase distortion.
harmonic distortion of every single frequency may also be hidden by the power of the other parts of the signal, if it isn't just a single sinewave (but who likes to listen to single sinewaves)
some thoughts to the 96 db:
from the 16 bit coding follows that the signal/noise ratio of a cd is 96 db for a sinewave using the full range.
but the signal/noise ratio lowers if the signal becomes more quiet.
if you have a longer period of quiet signal, the ear starts to get more sensible and starts to hear noise, because of the lower SNR.
additionally through quantization effects at low bit quantization, the noise produced is not white noise anymore, but becomes correlated to the signal such starting to produce artefacts which are more annoying than white noise.
those 2 effects are contraproductive.
this way the 16 bit of a cd are not that much, especially for music with longer quiet periods.
one way to hide this, is to have NO long quiet periods and the best results you get, if you have long equally full ranged loud periods.
