Laryngeal Function and
Speech Production
Learning Objectives
• Describe the basic role of the larynx in
speech and song.
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
Learning Objectives
• Possess a knowledge of laryngeal
anatomy sufficient to understand the
biomechanics, aerodynamics and
acoustics of phonation.
The hyo-laryngeal complex
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Extrinsic/Supplementary Muscles
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Intrinsic muscles
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Muscular Actions
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CA joint function
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Muscular actions on vocal folds
• Alter position
– Adduction
• LCA, IA, TA
– Abduction
• PCA
• Alter tension (and length)
– Increase/decrease longitudinal tension
• Balance between TA and CT
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Extrinsic/supplementary muscles
• Holds the larynx in the neck
• Allows positional change of the larynx
– Elevates when swallowing
– Elevates during certain speech activities
• Elevating pitch
• High vowel production
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The larynx
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“Layered” structure of vocal fold
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Basic Structure of the vocal fold
epithelium
connective tissue
superficial layer
tissue loosely connected to the other layers
Lamina
propria
intermediate layer
elastic fibers
Vocal ligament
deep layer
collagen fibers (not stretchy)
muscle (TA)
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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 the control variables of laryngeal
function.
Laryngeal Opposing Pressure
• Pressure that
opposes
translaryngeal air
pressure
• Sources
– Muscular pressure
– Surface tension
– Gravity
Laryngeal Airway Resistance
(LAR)
• Components of LAR
– Translaryngeal
pressure
– Translaryngeal flow
• Values can vary
widely
Resistance=Pressure/Flow
Glottal Size
Vocal Fold Stiffness
“Effective” Mass and Length
Learning Objectives
• Outline and briefly describe the different types of
sounds that can be produced by the larynx.
Laryngeal Sound Generation
• Transient vs. Continuous
– Glottal stops
• Aperiodic vs. Periodic
– Glottal fricatives
– Whispering
– Voice production/phonation
Laryngeal Sound Generation
Glottal stop
Glottal fricative
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 waveforms and
spectra 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
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
• Explain vocal fold motion using the 2-mass
model version of the myoelasticaerodynamic theory of phonation
Glottal Aerodynamics: Some Terminology
•
•
•
•
•
Subglottal pressure
Translaryngeal Pressure (Driving Pressure)
Translaryngeal Airflow (Volume Velocity)
Laryngeal Airway Resistance
Phonation Threshold Pressure
– Initiate phonation
– Sustain phonation
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
Definitions of terms
• Pme : myoelastic pressure (aka laryngeal
opposing pressure)
• Psg : subglottal pressure
• Patm: atmospheric pressure
• Pwg : pressure within the glottis
• Utg : transglottal (translaryngeal) airflow
•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 ↑ Pwg ↓ due to
Bernoulli effect
Pressure drop within the glottis
Bernoulli’s Law
P + ½  U2 = K
where
P = air pressure
 = air density
U = air velocity
Utg ↑ Pwg ↓ due to Bernoulli effect*
Pwg < Pme
M1 returns to midline
M2 follows M1 due to
mechanical coupling stiffness
Utg = 0
Pattern repeats 100-200 times a second
Role of glottal shape
• Current theories argue that Bernoulli effect
plays a relatively small role in vocal fold
closure.
• More important is glottal shape. Pwg is lower
for ‘divergent’ vs. ‘convergent’ shape.
• As the glottis become divergent, Pwg drops
resulting in the Pwg < Pme
Limitations of this simple model
Learning Objectives
• Describe how speakers control fundamental
frequency.
• Provide expected values for different measures
of fundamental frequency.
• Describe different methods for measuring
fundamental frequency.
• Describe how speakers control sound pressure
level.
• Provide expected values for different measures
of sound pressure level.
Quantifying frequency
• Hertz: cycles per second (Hz)
Non-linear scales
• Octave scale
– 1/3 octave bands
– Semitones
– Cents
• Other “auditory scales”: e.g. mel scale
Fundamental Frequency (F0)
Control
What factors dictate the vibratory frequency of the vocal folds?
• Anatomical factors
Males ↑ VF mass and length = ↓ Fo
Females ↓ VF mass and length = ↑ Fo
• Subglottal pressure adjustment – show example
↑ Psg = ↑ Fo
• Laryngeal and vocal fold adjustments
↑ CT activity = ↑ Fo
TA activity = ↑ Fo or ↓ Fo
• Extralaryngeal adjustments
↑ height of larynx = ↑ Fo
Characterizing
Fundamental Frequency (F0)
Average F0
•
•
speaking fundamental
frequency (SFF)
Correlate of pitch
• Infants
– ~350-500 Hz
• Boys & girls (3-10)
– ~ 270-300 Hz
• Young adult females
– ~ 220 Hz
• Young adult males
– ~ 120 Hz
Older females: F0 ↓
Older males: F0 ↑
F0 variability
• F0 varies due to
– Syllabic & emphatic stress
– Syntactic and semantic factors
– Phonetics factors (in some
languages)
• Provides a melody (prosody)
•
Measures
– F0 Standard deviation
• ~2-4 semitones for normal
speakers
– F0 Range
• maximum F0 – minimum F0 within a
speaking task
F0 in the first 10 years of life
F0 over the lifespan
Estimating the limits of vocal fold
vibration
Maximum Phonational Frequency Range
• highest possible F0 - lowest possible F0
• Not a speech measure
• measured in Hz, semitones or octaves
• Males
~ 80-700 Hz1
• Females ~135-1000 Hz1
• Around a 3 octave range is often considered
“normal”
1Baken
(1987)
Approaches to Measuring
Fundamental Frequency (F0)
• Time domain vs. frequency domain
• Manual vs. automated measurement
• Specific Approaches
•
•
•
•
Peak picking
Zero crossing
Autocorrelation
The cepstrum & cepstral analysis
Amplitude control during speech
Sound Pressure Level (SPL)
Average SPL
• Correlate of loudness
• conversation:
• ~ 65-80 dBSPL
SPL Variability
•  SPL to mark stress
• Contributes to prosody
• Measure
– Standard deviation for
neutral reading material:
• ~ 10 dBSPL
Estimating the limits of sound pressure
generation
Dynamic Range
• Amplitude analogue to maximum
phonational frequency range
• ~50 – 115 dB SPL
Learning Objectives
• Differentiate between different types of
vocal attack.
Learning Objectives
• Differentiate between different vocal
registers.
Vocal Register
• Refers to a distinct mode of vibration
According to Hollien…
• Range of consecutive Fos produced with a
distinct voice quality
• Fo range should have minimal overlap with
other registers
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Vocal Register
• Modal register (a.k.a. chest register)
• Pulse register (a.k.a. vocal fry, glottal fry,
creaky voice)
• Falsetto register (a.k.a. loft register)
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Voice Registers
Vocal Registers
Modal
–
–
–
–
–
–
VF are relatively short and thick
Reduced VF stiffness
Large amplitude of vibration
Possesses a clear closed phase
The result is a voice that is relatively loud and
low in pitch
Average values cited refer to modal register
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Vocal Registers
Pulse (Glottal fry)
–
–
–
–
–
–
30-80 Hz, mean ~ 60 Hz
Closed phase very long (90 % cycle)
May see biphasic pattern of vibration (open,
close a bit, open and close completely)
Low subglottal pressure (2 cm water)
Energy dies out over the course of a cycle so
parts of the cycle has very little energy
Hear each individual cycle
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Vocal Registers
Falsetto
–
–
–
–
–
–
–
500-1100 Hz (275-600 Hz males)
VF are relatively long and thin
Increased VF stiffness
Small amplitude of vibration
Vibration less complex
Incomplete closure (no closed phase)
The result is a voice that is high in pitch
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Learning Objectives
• Describe the physiological and acoustic
correlates of pressed, breathy and rough
voice qualities.
• Define terms such as harmonics (or
signal) to noise ratio, jitter and shimmer.
• Explain how physical description and
quantification of the phonatory signal can
be informative for clinical populations.
Vocal Quality
• no clear acoustic
correlates like pitch
and loudness
• However, terms have
invaded our
vocabulary that
suggest distinct
categories of voice
quality
Common Terms
• Breathy
• Tense/strained
• Rough
• Hoarse
Are there features in the acoustic
signal that correlate with these
quality descriptors?
Breathiness
Perceptual Description
• Audible air escape in the voice
Physiologic Factors
• Diminished or absent closed phase
• Increased airflow
Potential Acoustic Consequences
• Change in harmonic (periodic) energy
– Sharper harmonic roll off
• Change in aperiodic energy
– Increased level of aperiodic energy (i.e. noise), particularly in the
high frequencies
harmonics (signal)-to-noise-ratio
(SNR/HNR)
• harmonic/noise amplitude
•  HNR
– Relatively more signal
– Indicative of a normality
•  HNR
– Relatively more noise
– Indicative of disorder
• Normative values depend on method of
calculation
• “normal” HNR ~ 15
Harmonic peak
Amplitude
Noise ‘floor’
Harmonic peak
Noise ‘floor’
Frequency
First harmonic amplitude
From Hillenbrand et al. (1996)
Spectral Tilt: Voice Source
Spectral Tilt: Radiated Sound
Tense/Pressed/Effortful/Strained
Voice
Perceptual Description
• Sense of effort in production
Physiologic Factors
• Longer closed phase
• Reduced airflow
Potential Acoustic consequences
• Change in harmonic (periodic) energy
– Flatter harmonic roll off
Spectral Tilt
Pressed
Breathy
Acoustic Basis of Vocal Effort
Scatterplot
500.000000
Perception of Effort
Regression Adjusted (Press) Predicted
Value
Dependent Variable: effort
400.000000
300.000000
200.000000
100.000000
100.000000
200.000000
300.000000
400.000000
500.000000
effort
F0 + RMS + Open Quotient
Tasko, Parker & Hillenbrand (2008)
Roughness
• Perceptual Description
– Perceived cycle-to-cycle variability in voice
• Physiologic Factors
– Vocal folds vibrate, but in an irregular way
• Potential Acoustic Consequences
– Cycle-to-cycle variations F0 and amplitude
– Elevated jitter
– Elevated shimmer
Period/frequency & amplitude variability
• Jitter: variability in the period of each
successive cycle of vibration
• Shimmer: variability in the amplitude of each
successive cycle of vibration
…
Jitter and Shimmer
Sources of jitter and shimmer
• Small structural asymmetries
of vocal folds
• “material” on the vocal folds
(e.g. mucus)
• Biomechanical events, such as
raising/lowering the larynx in
the neck
• Small variations in tracheal
pressures
• “Bodily” events – system noise
Measuring jitter and shimmer
• Variability in measurement
approaches
• Variability in how measures are
reported
• Jitter
– Typically reported as % or msec
– Normal ~ 0.2 - 1%
• Shimmer
– Can be % or dB
– Norms not well established
Additional features of voice
• Regular fluctuations in frequency (and
amplitude)
– Vocal tremor
– Vocal “flutter”
• Irregular fluctuations in frequency
– Diplophonia and/or pitch breaks
Learning Objectives
• Briefly describe range of instruments used
to capture phonatory behavior including
stroboscopy, photoglottography,
electroglottography, and laryngeal
aeroydynamics.
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
• 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
Flow and Pressure
Measurement
Flow and Pressure
Measurement