When we were finally able to get the output levels of the two power amplifiers exactly matched, there was absolutely no audible difference when switching between them while listening to either white noise or music. During the adjustments of the amplifiers, it was demonstrated dramatically that minute differences in volume level (sound quantity) that are too subtle to be heard as such are interpreted by the ear as "obvious" differences in sound quality. Everyone was startled by the effect — everyone, that is, except Larry Klein, who had touched upon the phenomenon some time ago in his Audio Questions and Answers column