Pitch represents the perceived fundamental frequency of a sound. It is one of the three major auditory attributes of sounds along with loudness and timbre. When the actual fundamental frequency can be precisely determined through physical measurement, it may differ from the perceived pitch because of overtones, also known as partials, harmonic or otherwise, in the sound. The human auditory perception system may also have trouble distinguishing frequency differences between notes under certain circumstances. According to ANSI acoustical terminology, it is the auditory attribute of sound according to which sounds can be ordered on a scale from low to high.