Two tones an octave apart are perceived as having a kindred relationship - as being, in a sense, "the same note". This recognition of similarities for tones an octave apart is and was applying to any major musical culture all over the globe since the beginning of the history of man.

The sense of pitch associated with a tone has two different attributes: the frequency of the tone, the ”height”, and the chroma, which is a quality shared by all notes described by a particular letter. (Bachem 1950) Thus C2 and C3 are separated in pitch by an octave, they both have the same chroma - that associated with all C’s. They are in the same family.

In one interpretation of the pattern recognition theory of pitch, the brain searches for a distribution of peaks along the basilar membrane corresponding to a harmonic series of vibrations. On this basis, the fact that C2 and C3 evoke almost the same sensation can be readily understood.