P105 Lecture #26 visuals 18 March 2013

Anatomy of the Human Vocal Apparatus Illustration from E.J. Heller, “Why you hear what you hear”

Vocal Tract Anatomy – Another View Illustration from J. Sundberg, “The Acoustics of the Singing Voice”

Vocal Tract Anatomy – Another View Sound wave production starts with the larynx

Vocal Tract Anatomy – The Larynx Frontal view: View from above: Illustrations from E.J. Heller, “Why you hear what you hear”

Bernoulli Effect Discovered by Daniel Bernoulli in the mid 1700’s Essentially a consequence of conservation of energy Statement is that pressure and flow velocity are inversely related for incompressible (approx. constant density) fluid Mathematically: p1 + ½ r1 v12 = p2 + ½ r2 v22 (where p = pressure, r = density, v = velocity)

Function of the Vocal Folds Can think of the vocal folds as a mass/spring system. Operates via Bernoulli Effect: expulsion of air from lungs  high flow through glottal opening Low pressure closes vocal folds flow stops folds open Repeat. Illustration from A.H. Benade, “Fundamentals of musical acoustics”

Net Result: Periodic expulsion of “puffs” of air from lungs Top: volume velocity vs time for sound production at 125 Hz (male voice); Bottom: Power spectrum falls at 12 dB per octave Fourier Spectrum: From Rossing, Wheeler & Moore, The Science of Sound

Sound Production Summary Expulsion of air from lungs induces vibration of vocal folds (via the Bernoulli effect). The vocal folds open and close with a frequency dictated by anatomy (geometry) plus applied tension (contraction of muscles connecting folds with cartilage). Give rise to periodic puff emission with fundamentals around 100 Hz (male), 200 Hz (female), 300 Hz (children). These are just the vocal fold vibration frequencies. Thus, the vocal fold vibration frequency sets the pitch To understand harmonic structure of speech must also take into account the filtering effect of the vocal tract  next up.