Multi-dimensional Pitch – A Moving Target
When referring to pitch, we think about how high or low a note is on a relative scale. Pitch is an acoustic carrier of meaning, as the different phonemes of speech and the overall intonation of voice is denoted by changes in pitch. Melody is also made possible by pitch modulation. Aside from emotional and language constructs, pitch also aids in our localization of sounds and guides us in our perception of an object’s size, speed and distance. Pitch is therefore critical to our analysis of the world and in the conveyance of meaning and emotion.
In western musical tradition, sounds are subdivided into octaves containing seven tones and twelve semi-tones. The human ear is capable of detected pitches over a ten octave span, although instrumental scales are generally confined to eight, as it is neither practical nor particularly pleasing to produce notes at the limits of human pitch perception.
Numerous other scales have been used at different times in other cultures, giving music a cultural identity. Our western Greek chromatic scale is based on the concept of harmony or sameness of notes (chromas) occurring eight tones apart. For example, if two A keys on the piano are struck simultaneously two octaves apart, they produce a kind of smoothness (consonance). If the same two A keys are played successively, they produce a kind of sameness (affinity). Notes occurring five tones apart (a fifth) are similarly sympathetic to one another. Other intervals in an octave produce varying degrees of dissonance when played together or signify musical progression when played successively.
“Pitch” is a perceptual concept and is derived from the “frequency” of sound. Psycho-acoustic science looks at how the physical properties of sound correlate with perceptions of sound in the mind. The relationship between frequency and pitch is especially complex.
At the physical level, sounds are repeating cycles of molecular compression and rarefaction resulting in pressure waves. The number of cycles completed per second (measured in Hertz or Hz) denotes the frequency of a sound. The faster a cycle is completed, the shorter the wavelength, and the higher the perceived pitch. Human ears are capable of detecting frequencies from 20 to 20,000 Hz.
Various theories of pitch perception have been proposed over the years, but none has been able to completely explain the human ear’s pitch range. Today’s theory of pitch perception relies on a blending of three main principles. Temporal, volley and place theories, when combined, best explain the limits of human pitch perception. These individual pitch theories will be examined at another time.
The resolution of our pitch perception depends on the frequency, duration and magnitude of sounds. Frequencies at the extremes of human pitch perception only take on pitch-like qualities at higher volume and with longer signal duration. Our judgement of pitch is also affected by the presence of multiple frequencies (e.g. overtones) in complex sounds, which is actually the norm in our environment. Perhaps for reasons of pragmatism, our auditory systems are most sensitive to pitch variations occurring within the human voice spectrum.