Virtual pitch

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Virtual pitch is a term used to describe the phenomenon in which one's brain interprets tones in music that don't actually exist. This is in contrast to a spectral pitch, which is a tone that physically exists.

The term was coined by Professor Ernst Terhardt from Technical University of Munich in 1970 ^[1].

[edit] Theory

Virtual pitch is an experimentally established phenomenon in humans that can be mathematically described. In its basic form, given a series of pitches together in a chord, one will hear an approximate fundamental frequency with intensity depending on how close the pitches are to exactly matching the harmonics of the fundamental. This is done by finding the greatest common divisor of a set of frequencies to a certain degree of accuracy, and factoring everything in to calculate how intense the virtual tone might be relative to the existing tones. It is easily visualized by plotting sine waves at several harmonic frequencies and deleting the fundamental, along with any other tones one desires. The resulting wave still has a visible period corresponding to the fundamental frequency because it as at this point that all higher harmonics constructively interfere.