Topic 3b: Phonation

Learning Objectives Possess a knowledge of laryngeal anatomy sufficient to understand the biomechanics and acoustics of phonation

Behrman Chapter 5, 6 Place less emphasis on… Minor anatomical landmarks and features Extrinsic muscles of the larynx Blood supply to the larynx Central motor control of larynx Peripheral Sensory control of larynx Stress-Strain Properties of Vocal Folds

What is the basic role of the larynx in speech and song Sound source to excite the vocal tract Voice Whisper Prosody Fundamental frequency (F0) variation Amplitude variation Realization of phonetic goals Voicing Devoicing Glottal frication (//, //) Glottal stop (//) Aspiration Para-linguistic and extra-linguistic roles Transmit affect Speaker identity

The vocal fold through life… Newborns No layered structure of LP LP loose and pliable Children Vocal ligament appears 1-4 yrs 3-layered LP is not clear until 15 yrs Old age Superficial layer becomes edematous & thicker Thinning of intermediate layer and thickening of deep layer Changes in LP more pronounced in men Muscle atrophy

Learning Objectives Describe a single cycle of vocal fold oscillation Describe why phonation is considered “quasi-periodic” Describe the relationship between vocal fold motion (kinematics), laryngeal aerodynamics and sound pressure wave formation Describe and draw idealized representations of the glottal sound source

Complexity of vocal fold vibration Vertical phase difference Longitudinal phase difference

The Glottal Cycle

Phonation is actually quasi-periodic Complex Periodic vocal fold oscillation Aperiodic Broad frequency noise embedded in signal Non-periodic vocal fold oscillation Asymmetry of vocal fold oscillation Air turbulence Voicing vs. whispering

Flow Glottogram

Synchronous plots Sound pressure waveform (microphone at mouth) Glottal Airflow (inverse filtered mask signal) Glottal Area (photoglottogram) Vocal Fold Contact (electroglottogram)

Sound pressure wave sound pressure Instantaneous Time

Learning Objectives Briefly describe range of instruments used to capture phonatory behavior Explain vocal fold motion using the 2-mass model version of the myoelastic-aerodynamic theory of phonation

Measuring Glottal Behavior Videolaryngoscopy Stroboscopy High speed video

Photoglottography (PGG) illumination Time

Electroglottography (EGG) Human tissue =  conductor Air:  conductor Electrodes placed on each side of thyroid lamina high frequency, low current signal is passed between them VF contact  =  impedance VF contact  =  impedance

Electroglottogram

Glottal Airflow (volume velocity) Instantaneous airflow is measured as it leaves the mouth Looks similar to a pressure waveform Can be inverse filtered to remove effects of vocal tract Resultant is an estimate of the airflow at the glottis

Glottal Aerodynamics Volume Velocity Driving Pressure Phonation Threshold Pressure Initiate phonation Sustain phonation Laryngeal Airway Resistance

Myoelastic Aerodynamic Theory of Phonation Necessary and Sufficient Conditions Vocal Folds are adducted (Adduction) Vocal Folds are tensed (Longitudinal Tension) Presence of Aerodynamic pressures (driving pressure)

2-mass model Upper part of vocal fold Mechanical coupling stiffness Lower part of vocal fold Coupling between mucosa & muscle TA muscle

VF adducted & tensed → myoelastic pressure (Pme ) Glottis is closed subglottal air pressure (Psg) ↑ Psg ~ 8-10 cm H20, Psg > Pme L and R M1 separate Transglottal airflow (Utg) = 0 As M1 separates, M2 follows due to mechanical coupling stiffness Psg > Pme glottis begins to open Psg > Patm therefore Utg > 0

Utg ↑ ↑ since glottal aperature << tracheal circumference Utg ↑ Ptg ↓ due to Bernoulli effect Pressure drop across the glottis Bernoulli’s Law P + ½ U2 = K where P = air pressure  = air density U = air velocity

Utg ↑ Ptg ↓ due to Bernoulli effect Plus “other” aerodynamic effects Ptg < Pme M1 returns to midline M2 follows M1 due to mechanical coupling stiffness Utg = 0 Pattern repeats 100-200 times a second

Limitations of this simple model