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 “quasiperiodic”
• 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)
Instantaneous
sound pressure
Sound pressure wave
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 myoelasticaerodynamic theory of phonation
Measuring Glottal Behavior
• Videolaryngoscopy
– Stroboscopy
– High speed video
illumination
Photoglottography (PGG)
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