Terhardt, E. (1971). Pitch shifts of harmonics, an explanation of the octave enlargement phenomenon. In: Proc. 7th Intern. Congr. Acoust., Budapest (3), 621-624

It is demonstrated that the pitches of individual harmonics of a complex tone differ from the pitches of the same harmonics when presented in isolation. For fundamental frequencies of 100, 200, and 400 Hz, the pitches of the first four harmonics were measured with four subjects. In all cases, the first harmonic tended to be shifted slightly (i.e., by 0...1%) down, the other harmonics, up. The upward shift of harmonics No. 2 to 4 was the more pronounced the higher the harmonic number (0.5 ... 6%). The effect of those pitch shifts on the pitch intervals corresponding to the musical octave is discussed. It is shown that the phenomenon of octave enlargement of successive tones observed earlier can be explained by the described pitch shifts of harmonics.

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