Virtual Pitch & Timpani
The theory of Virtual Pitch was developed in 1969-1970 by Prof. Ernst Terhardt (Technische Universitat Munchen).15 Terhardt’s theory extends Giuseppe Tartini’s terzo suono (third sound), J. P. Rameau’s theory of fundamental bass, August Seebeck’s theory of periodicity pitch and J. F. Schouten Pitch of the Residue theory; all deal with the phenomenon of the missing fundamental created by resultant tones.
Virtual pitch is a phenomenon where the processing center of the 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 in the spectrum. In its simplest form, when given a series of pitches, which are a part of a harmonic overtone series, one may hear an approximate fundamental frequency if the pitches are a close enough match to the harmonics of the fundamental. The perception of virtual pitch is controversial because there is some variability from listener to listener based on how the individual perceives pitch. It also depends on the loudness (sound pressure level, SPL) of the sounds, and the mixture of the partials. Complex sounds almost never fuse completely into a single pitch, instead they produce a spectrum, and which pitch from the spectrum is most prominent can depend on the musical context. This is still an active area of research in the psychological acoustics community.
Dr. Robert Ehleehle, Professor of Music University of Northern Colorado demonstrates prof. Ernst Terhardt’s classic virtual pitch experiment.
Virtual Pitch Demonstration
courtesy of theflyingrobby
Does virtual pitch exist in timpani pitch?
Timpani pitch (at its best) will always be a compromise of true harmonic pitch. No matter how hard one tries to temper or balance a head, it can never produce a true harmonic series. Humans are hard-wired to recognize sounds as being pitched only if they have numerous strong harmonic overtones. The lack of numerous strong harmonic overtones in timpani pitch can make tuning problematic for some people. (see Seebeck vs. Ohm) Contemporary theories on pitch perception are moving towards two basic types of listeners, spectral and holistic.14 There are of course, combinations of the two. The spectral listener tends to breakdown a sound and hear it more as group of individual frequencies rather than a single sound. The holistic listener tends to group all of the frequencies into a single sound. The predominantly spectral listener could easily be confused by the lack of strong harmonic overtones and the myriad of non-harmonic overtones found in timpani pitch. The predominantly holistic listener might mistake a dark or bright sound as being a flat pitch or sharp pitch respectively. Most seasoned timpanists are both spectral and holistic listeners and switch seamlessly between the two. They have to know which overtones to ignore and which ones to listen to when dealing with timpani pitch. This is especially true when it comes to the process of tempering heads.
Most people hear the actual pitch of the instrument as being that of the principal tone, mode 1,1, which is actually the second partial of the vibrating membrane. Since human perception of virtual pitch depends to a great extent on the loudness (sound pressure level, SPL) and the strength and duration of the overtones, the missing fundamental may not be perceived if the partials are not harmonic enough or strong enough. Some timpanists describe an indistinct sound an octave below the principal tone when the drum is struck with a soft mallet at certain spots.16 Timpani virtual pitch may or may not also be perceived by the human ear due to one’s propensity for being a spectral listener and not a holistic listener (see above). Once the virtual pitch of a well tuned timpano has been reached it can also be destroyed when mode 2,1 (the fifth) becomes to predominate in the spectrum (see Pleading the Fifth).
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