Quote Originally Posted by Woochifer
It might just have to do with how human hearing has differing sensitivities at different frequencies. At low levels, we simply hear the highs and lows differently than we do at higher levels.
I think you've nailed it here. My employer's health plan requires hearing tests annually. The one that I've thought I've failed twice now is the one where a chord consisting of 3 or 4 notes is played while the volume increases over 90 seconds or so. Dammit if the prominent notes don't change as the volume does. According to the techie they don't really change, it's just that the vast majority of people perceive that it does. Something about the time you notice the note change is used to calculate when your hearing "shifts" at which volumes, etc. You'd swear the chord changes from a major to it's relative minor (C to A minor, IRC) at some points

Could also explain why some people are tone deaf?