Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange; bass and treble sounds "seem" reduced in intensity at lower listening levels. The Fletcher-Munson effect is the name given to this psychoacoustical phenomenon in which the human ear perceives much less bass and somewhat less high frequencies as the volume of the sound is lowered. It is named for the two people who discovered it.