Understanding certain things about sound frequencies can really help us in the home studio. Psycho-acoustics is the effect that sound has on our psyche, mood, etc. Here is a really interesting article about certain sounds that make us cringe, sometimes just by think about them. This particular sound actually causes a physical change, for me anyway, when I think about or hear it. I refer, of course, to the infamous scratching of fingernails on a chalkboard.