Until the late 1960s, the prevalent concept of pitch was unitary. It was presumed that pitch, as an auditory (i.e., psychological) attribute, is of one and the same kind, regardless by what type of sound it is elicited. However, already in the 19th Century it had become apparent that in the frame of this concept it was impossible to reconcile a number of fundamental and well established observations. On the one hand, it was evident that the pitch of sine tones with high probability is a "place pitch", i.e., is dependent on the place of maximal excitation of the cochlear partition, and such eventually is a result of peripheral auditory Fourier analysis. On the other hand, it was evident that the pitch of many types of complex tone cannot be explained by that principle - in particular, the pitch of harmonic complex tones whose fundamental Fourier component is weak or entirely missing. Until present days, attempts have been made to resolve this conflict by searching for a parameter of sound and a mechanism that accounts both for the pitch of sine tones and of complex tones. The search as yet was a failure.
I was, and still am, convinced that within the unitary concept of pitch this failure is inevitable. This is why in 1967/68 I began to explore the alternative concept that besides the pitch of sine tones there is another type of pitch, namely, virtual pitch. The existence of the latter type of pitch could indeed be verified, such that a strict distinction became necessary between the two types of pitch. This is why I proposed the term spectral pitch (Spektraltonhöhe) [17] , [18] , [22]. The conceptual distinction between spectral pitch and virtual pitch at once resolved the above conflict. The solution is that both spectral pitch and virtual pitch ultimately are dependent on aural Fourier analysis; however, while any spectral pitch is conceived as immediately corresponding to a spectral singularity, virtual pitch is modeled as being deduced from a set of spectral pitches on another stage of auditory processing [10]. The relationship between spectral pitch and virtual pitch is in many respects analogous to that between primary and virtual visual contour.
So, spectral pitch is defined as an elementary auditory object that immediately represents a spectral singularity. The simplest and most prominent example is the pitch of a sine tone. Here are a few more examples:
There is hardly any sound that does not elicit any spectral pitch at all. The harmonic complex tones of real life, i.e., voiced speech and musical tones, are aurally represented by a number of spectral pitches that correspond to the lower harmonics. The formants of speech vowels elicit corresponding spectral pitches. Even random sound signals often are either "colorized" by spectral irregularities, which will give rise to steady spectral pitches, or there can occur instantaneous irregularities in the short-term Fourier spectrum that elicit spectral pitches of which both the height and the instant of occurrence are random. When, and if, any real-life sound (e.g., foot step, knock at the door, splashing water, sound of a car's engine, fricative phoneme of speech) can be identified by ear, one can be sure that - besides temporal structure - spectral pitch is involved. Spectral pitch is the most important carrier of auditory information, as it is an element of higher-order, Gestalt-like types of auditory percepts such as, e.g., the pitch of musical tones, the strike note of bells, the root of musical chords, the quality of a particular vowel.
Spectral pitch exhibits a considerable number of interesting and significant properties such as pitch shifts, octave stretch, and binaural diplacusis, "after-images" (Zwicker 1964a, Wilson 1970a), and "enhancement" effects (Schouten 1940c, Viemeister 1980a, Wartini 1996a), [104] p. 316-345. Although it is evident that spectral pitch emerges from an analysis of the spatio-temporal distribution of the cochlear partition's excitation, it not clear in detail how this is accomplished. To my knowledge, as yet there does not exist a model that accounts for all the established phenomena about spectral pitch.