The Quasi-Periodic Structure of Human Sound

This paper develops a dynamical account of human sound systems, arguing that the diversity of speech sounds emerges from a constrained physical landscape shaped by the anatomy of the vocal tract, the perceptual structure of the auditory system, and the pressures of long-term transmission. Although the space of possible sounds is continuous, only a limited number of articulatory and acoustic configurations remain stable under repeated use. These stable configurations function as attractor states: positions that are easy to produce, easy to perceive, resistant to noise, and therefore likely to persist across generations. Human sound systems are interpreted not as arbitrary cultural constructions but as emergent equilibria that repeatedly organize around these stable regions. The paper examines how attractor states arise from the geometry of the vocal tract and the resonance properties of speech production. Open vocal tract configurations generate stable resonant patterns that form the foundation of communication, while constrictions and closures modify, interrupt, or shape these resonances to create contrast. Meaning depends on contrasts that remain distinct despite production variability, environmental noise, and imperfect transmission. Stable contrasts survive because they align with both articulatory ease and perceptual reliability, while fragile distinctions tend to merge, simplify, or disappear over time. Sound systems are described as dynamical structures shaped by competing forces. Simplifying pressures favor stability, efficiency, and reliable transmission, while complicating pressures introduce variation through social identity, innovation, borrowing, and individual differences. The interaction of these forces produces structured recurrence rather than random change. Across populations and historical periods, sound inventories repeatedly drift toward familiar attractor regions because the underlying biological and perceptual constraints remain constant. Child language acquisition reinforces this process by preferentially stabilizing robust contrasts and filtering unstable ones. Evidence from cross-population recurrence, historical sound change, and the repeated emergence of similar sound inventories suggests that long-term drift follows predictable pathways through attractor space. Fragile distinctions frequently collapse, highly marked sounds tend to simplify, and newly emerging communication systems often converge on familiar stable configurations. Modern transmission environments introduce additional pressures through compression, filtering, and machine-mediated communication. While these technologies do not replace traditional articulatory and perceptual constraints, they may amplify long-standing tendencies by favoring signals that remain robust across both biological and digital channels. The paper proposes that human sound systems exhibit structured recurrence: a recurring set of stable configurations that reappear across populations despite cultural divergence. Drawing on biomechanics, signal theory, perception, and dynamical systems, it argues that sound inventories are shaped by a constrained landscape of attractor states rather than unrestricted variation. This framework generates testable predictions concerning the persistence of highly salient contrasts, the fragility of marginal distinctions, the influence of digital transmission environments, and the convergence of newly formed communication systems. Human sound systems are therefore understood as long-term equilibria produced by the interaction of physical constraints, perceptual thresholds, transmission pressures, and adaptive variation acting across generations.