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Introduction
Science-based voice pedagogy curricula routinely focus on the anatomy and physiology, vocal fold dynamics, kinesiology, vocal tract acoustics, and motor learning properties of the singing body. The role of the hearing mechanism in defining the sound of a singer is frequently under-explored. However, the human senses are physical systems with limitations that shape one's mental image of reality. This mental image is called a percept. The eye cannot produce a detailed image of a very far or very near object, and sensitivity to touch is not uniform across the entire body. Such limitations change the percept of, rather than the objective nature of, an object. As the sound wave produced by a voice is a physical phenomenon, one can explore the underlying rules of hearing to ask how one might possibly perceive the human voice. This is another way of asking what sounds the human voice is capable of making.
This may seem like an academic, tree-falling-in-the-woods distinction: that all the richly colored and varied sounds we hear exist as a silent, colorless soup of vibrating air until they are perceived. However, sound waves can be understood as instructions for timbre, not the timbre itself. The way in which the human hearing mechanism reacts to those instructions limits, colors, and in some cases creates aspects of the voice. Psychoacoustics is the field of study concerned with these phenomena. This article will explore and synthesize three such psychoacoustic limitations relevant to singing: auditory roughness, the resolvability of harmonics into the pitch, and absolute spectral tone color. My hope is that the resulting framework may inform the way that registration, vowels, and formants1 are taught in the voice pedagogy classroom.
Roughness
Auditory roughness is a buzzing, sometimes pulsing or beating quality introduced by the inner ear because the cochlea is unable to differentiate simple tones that are very close in frequency. This is true whether these simple tones are sine tones or narrowly notch filtered noise from different sources, or adjacent harmonics of a single, pitched sound. Generally, any two simple tones a minor third or closer will give rise to such roughness; the closer, the rougher. This interval, called a critical band, is wider at lower frequencies.2 However, for much of the singable range, the...