From Wikipedia on "Psychoacoustics":
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In many applications of acoustics and audio signal processing it
is necessary to know what humans actually hear. Sound, which consists
of air pressure waves, can be accurately measured with sophisticated
equipment. However, understanding how these waves are received and
mapped into thoughts in the human brain is not trivial.

Recognizing features important to perception enables scientists and
engineers to concentrate on audible features and ignore less important
features of the involved system. It is important to note that the
question of what humans hear is not only a physiological question
of features of the ear but very much also a psychological issue.
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There's more in that article if you're interested.


noise perception is a very psychological thing (think of all those crazy
psycho-acoustic models for Hi-Fi audio noise reduction),

Not sure about that.