Phonation
Note: Audio demos made with fsyn:
original pitch, monotone, and
inverted pitch. FDR demo original
pitch and monotone only.
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Information Conveyed by the Source
For voiced speech, the spectrum of the laryngeal buzz
constitutes the source part of source-filter theory. A great deal
of the burden of phonetic coding is carried by the filter (e.g.,
[b]-[d]-[g]; [s]-[ʃ]; [ɑ]-[i]-[u]-[ʌ]-[ɚ], etc.) But, a good deal of
speech information is conveyed by the source. For example:
1. Intonation (melodic) contour: Pattern of f0 over time
conveys information about the grammatical structure of the
utterance (e.g., phrase boundaries and sentence type), as
well as affective information.
2. Rhythmic pattern: Pattern of stressed and unstressed
syllables can convey lexical information (OBject vs.
obJECT) and emphatic stress (e.g., given vs. new).
3. Loudness: Controlled mostly at the source (but filter has
some effect on loudness as well).
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4. Voice quality:
•
•
•
•
•
•
•
•
•
•
Clear or “modal” phonation
Whisper
Breathiness (buzz and hiss combined)
Roughness
Hoarseness
Diplophonia (two simultaneous f0s/pitches)
Pressed or strained voice
Glottal fry
Falsetto
You name it: many other hard-to-classify, hard to
characterize variations in vocal quality
5. Some segmental phonetic information:
Example: Timing of voicing onset relative to articulatory release
is a major cue to the voice-voiceless distinction (more later)
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Cricoid lamina is
in back
Cricoid arch is in
front
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< View from
the top
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CRICOTHYROID JOINT
Note that when the cricoid moves up (i.e., closing the gap between
the cricoid and the thyroid in front), the arytenoids are rotated
away from the thyroid angle. We will see that this has a lot to do
with the control of fundamental frequency.
Figure from
David Broad (in
Minifie et al., 1973,
Normal Aspects of
Speech, Hearing &
Language)
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MOTIONS OF THE ARYTENOIDS
Gliding motion of arytenoids brings VFs
toward midline.
Figure from
David Broad (in
Minifie et al., 1973,
Normal Aspects of
Speech, Hearing &
Language)
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Figure from
David Broad (in
Minifie et al., 1973,
Normal Aspects of
Speech, Hearing &
Language)
Thyroid Notch This Way->
ROCKING MOTION OF ARYTENOIDS
Rocking forward (toward thyroid angle) brings VFs forward
(obviously) and (less obviously) toward midline. Rocking
backward (away from thyroid angle) brings VFs backward
(obviously) and (less obviously) away from midline.
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Five Layers of VFs:
1. Epithelium (very thin, very flexible)
2. Superficial layer of LP (thin, gelatinous, very flexible)
3. Intermediate layer of LP (rubbery, less flexible)
4. Deep layer of LP (like thick thread)
5. Vocalis muscle
“Cover-Body” Organization of VFs:
Cover= Epithelium + Superficial LP
Transition= Intermediate &Deep Layers of LP
Body = Vocalis muscle
It is the cover which is most heavily involved in VF
vibration – both the side-to-side motion that we all
know about, but also the up and down motion that you
may be less familiar with. Hillenbrand: Phonation
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Sequence of events in phonation, beginning with:
Steady lung pressure
Steady flow thru VFs
Abducted VFs (i.e., away from midline)
1. A steady (DC) muscular force is applied to adduct the folds; i.e., to
bring the VFs toward midline.
A ↓
Vo ↓ (volume velocity; i.e., air flow)
V ↑ (particle velocity)
2. Bernoulli force increases: The Bernoulli Principle states that an
increase in particle velocity is accompanied by an aerodynamic
force that is exerted at right angles to the angle of flow.
FB FB
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The other way to think about FB is to think of it as a drop in pressure or
sucking force inside the glottal aperture. Either way, the result is a force that
bring the VFs toward midline.
3. Muscular force and Bernoulli force combine to bring the VFs to midline,
where they meet.
A =
Vo =
V =
FM =
FB =
Psg =
Zero (Glottal Area)
Zero (Volume Velocity; i.e., airflow)
Zero (Particle Velocity)
Steady (Muscular force)
Zero (Bernoulli force)
Very rapid and dramatic increase (Subglottal pressure)
4. When folds meet at midline, there are two opposing forces acting:
the muscular force acts to keep the VFs approximated
Psg acts to blow the VFs apart and upward
At some point, Psg will reach a high enough value to win the contest, and:
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5. VFs are blown apart (and up), moving away from midline
A ↑ (glottal area)
Vo ↑ (volume velocity; i.e., air flow)
V ↓ (particle velocity)
6. The mvt of the VFs away from midline is opposed by:
The DC muscular force (which is still in effect)
The elasticity of the VF tissue
The VFs will move toward midline again, and the process is
repeated, from step 1.
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Vibratory Motion of the
Vocal Folds . Note the
“Vertical Phase
Difference”; i.e., the VFs
open bottom edge 1st,
followed by top edge;
close bottom edge 1st,
followed by top edge.
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Note that when the VFs
separate, they do not just
move side-to-side. The
folds – especially the top
edge – are also displaced
upward quite a bit. This
is not surprising given the
upward direction of the
aerodynamic force that
causes them to separate
in the first place.
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THE TWO-MASS MODEL OF
PHONATION
These little dealies
represent the
viscosity of the
vocal fold tissue.
We’ll ignore that
and focus on the
spring-mass system.
Note that the two masses of the vocal folds are
represented by a spring and mass system. What factors
will control the vibrating frequency of this system?
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ANOTHER VIEW OF THE
TWO-MASS MODEL
Note that VFs open bottom edge followed by top edge,
and close bottom edge followed by top edge.
Light gray =
top edge
View
from
above->
Dark =
bottom edge
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Control of F0 in the Two-Mass Model
Fundamental Frequency Can be Increased by:
1. Increasing Stiffness: This is done by increasing the longitudinal tension of the VFs,
exactly like stretching a rubber band. The stiffness increase results in an increase
in natural vibrating frequency.
2. Decreasing the Effective Mass of the VFs: When the VFs are stretched, a smaller
portion of the folds vibrates. This is equivalent to decreasing the mass of the VFs.
The decrease in mass results in an increase in natural vibrating frequency.
MORAL:
Longitudinal Tension ↑ f0
↑
Longitudinal Tension ↓ f0 ↓
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INTRINSIC LARYNGEAL MUSCLES
AND THE CONTROL OF F0
Four paired muscles (i.e., one on left, one on right), one unpaired
muscle.
Paired:
1. Lateral Cricoarytenoid (LCA)
- Adductor (Closer)
2. Posterior Cricoarytenoid (PCA)
- Abductor (Opener)
3. Cricothyroid (CT)
- Longitudinal tension increaser/decreaser
4. Thyroarytenoid (TA) [Internal (vocalis) / External]
- Function depends on behavior of other muscles
Unpaired:
Interarytenoid (IA) [Transverse & Oblique]
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LATERAL CRICOARYTENOID (LCA)
This muscle pulls downward and forward on the arytenoids.
Contraction has the effect of rocking the arytenoids forward.
Given the “toe in” angle of the arytenoids, this forward rocking
motion adducts (closes) the VFs (and may increase medial
compression; i.e., squeezing force).
The LCA may also reduce the longitudinal tension on the VFs.
(Note: Only the right LCA is shown in this picture.)
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Posterior Cricoarytenoid (PCA)
This muscle pulls back on the arytenoids. This has the effect of
rocking the arytenoids backward. Given the “toe in” angle of the
arytenoids, this backward rocking motion abducts (opens) the
VFs.
The PCA may also increase the longitudinal tension on the VFs.
View from the Back
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Cricothyroid Muscle (CT)
This muscle pulls the cricoid up, reducing the distance between
the cricoid and the thyroid. Most Important: This movement
rotates the cricoid lamina back and away from the thyroid notch.
This pulls the arytenoids away from the thyroid notch, increasing
the tension on the VFs.
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Main Point: The CT increases the longitudinal tension of
the VFs, decreasing effective mass, and increasing f0.
Figure from
David Broad (in
Minifie et al., 1973,
Normal Aspects of
Speech, Hearing &
Language)
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Thyroarytenoid Muscle (TA)
• Note internal and external parts of TA.
• Internal TA also called vocalis muscle.
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Interarytenoids (IA)
• Note transverse (side-to-side) and oblique parts of IA.
• Contraction of IA (transverse and oblique) produces gliding
motion of arytenoids; result is adduction and medial
compression (squeezing).
• Contraction of oblique IA may also cause apices of
arytenoids to approximate.
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Relationship Between Glottal Area and
Glottal Volume Velocity (Air Flow)
• When area is large, flow is high. No big surprise:
When a faucet is full on, flow is high.
• The flow waveform is a steeper than the area
waveform. (Flow is proportional to Area3; e.g., if
area is doubled, flow increases by a factor of 23= 8.)
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Time Organization/Frequency Organization
There is a close and predictable relationship between
the shape of the glottal pulse and the spectrum of that
pulse.
When the slope of the glottal wave is steep (more like
an impulse), there will be a lot of energy spread into
the higher frequency harmonics.
When the slope of the glottal wave is gradual (more
like a sinusoid), there will be less energy spread into
the higher frequency harmonics.
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Time Organization/Frequency Organization
This figures shows just two extremes:
• A nearly impulse-like waveshape (high time organization –
events are “compressed” in time) with lots of energy spread
to the upper harmonics (low frequency organization).
• A nearly sinusoidal waveshape (low time organization –
events are spread evenly over time) with nearly all of the
energy at the fundamental frequency (high frequency
organization).
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Time Organization/Frequency Organization
Note that more
impulsive-looking
waveforms produce
more energy spread
into the higher
frequencies. The more
smooth and sinusoidallooking waveforms
have a greater amount
of their energy
concentrated at the 1st
harmonic (f0), and less
energy in higher
frequency harmonics.
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Effects of Gradual vs.
Abrupt Glottal Closure
Gradual closure,
energy concentrated
strongly at f0.
More abrupt closure,
more energy spread
to harmonics above f0.
The glottal waveforms above differ only in the abruptness of glottal
closure. Notice that the glottal waveform with more gradual closure is
fairly weak in higher frequency harmonics. Conversely, the glottal
waveform showing more abrupt closure shows stronger upper
harmonics. Rapid glottal closure is accomplished mainly by the lightest
and most flexible portion of the VFs – the VF cover (epithelium & superHillenbrand: Phonation
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ficial layer of the LP).
MORAL: Time organization and frequency
organization are inversely related.
• When time organization is high (like an impulse),
frequency organization is low (energy is spread or
“splatters” into the higher frequencies).
• Conversely, when time organization is low (like a
sinusoid), frequency organization is high (energy is
concentrated near a single frequency).
SO:
• Transient-looking waveforms have a lot of energy
spread into the higher frequencies.
• Sinusoidal-looking waveforms have most of their
energy near the fundamental.
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