A phenomenon in which sound sources that have certain complex overtone structures can appear to have a pitch that is lower than the lowest frequency present in the sound. As an example, certain bar and rod chimes, because they produce overtone structures at non-integer ratios, can produce a set of frequencies which are close to the 2nd, 3rd, 4th, etc., harmonics of an apparent fundamental frequency that is not actually present. If the harmonics are in reasonable ratios so as to mimic common sound sources than the ear is accustomed to hearing, then the ear will tend to "fill in" the missing fundamental. The chime then sounds (or seems to) a note whose fundamental frequency is lower than what the rod or bar is capable of producing, based on its physical dimensions. Because the perceived tone