Anatomy of the vocal mechanism

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1/21/09
Anatomy of the vocal mechanism
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Phonation
•  Myoelastic aerodynamic theory of
phonation.
•  Fundamental frequency
•  Harmonics
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Phonation
•  Production of sound in larynx.
•  Anytime you use voicing to produce a
sound (e.g., vowels and voiced consonants)
phonation will take place.
•  Myoelastic aerodynamic theory of
phonation (see next slide)
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Myoelastic Aerodynamic Theory
of Phonation
•  Two stage process
•  Stage one: Myoelastic phase. Elasticity of
vocal folds helps them close.
•  Stage two: Aerodynamic phase
–  Sub-glottal pressure forces vocal folds apart
–  Bernoulli Effect helps vocal folds close
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Bernoulli Effect
•  As air velocity
increases, air
pressure
decreases.
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Myoelastic Aerodynamic Theory
of Phonation (continued)
•  Another way of stating the MA theory is to
see how vocal folds open and close.
•  Opened due to…
–  Increase in subglottal pressure
•  Closed due to…
–  Vocal fold elasticity
–  Bernoulli effect
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Fundamental Frequency
• 
• 
Refers to the fundamental frequency to which the
vocal folds vibrate at.
Variables that affect fundamental frequency (fo)
1.  Gender and age
• 
• 
• 
Males
Females
Children
120 Hz
220 Hz
270-300 Hz
2.  Mass (relaxing and tensing of vocal folds)
3.  Intensity (Bernoulli effect)
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Harmonics
•  Discussed during acoustics section.
•  Remember… –  During phonation you will fo along with a
series of harmonics
–  Spacing between harmonics will equal the fo.
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Harmonics
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Jitter and Shimmer
•  Jitter
–  Variations in the Fo, aka frequency perturbation
–  Periods between individual cycles vary slightly
(e.g., 200, 201, 199 Hz, etc.)
•  Shimmer
–  Variations in Intensity, aka amplitude
perturbation
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Jitter and Shimmer continued
•  Causes of jitter and shimmer
–  Neurological
–  Biomechanical
–  Aerodynamic
–  Acoustic (hearing loss)
•  Normal values
–  Jitter (0.2 to 1%) of frequency
–  Shimmer (< 0.5 dB)
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Jitter and Shimmer continued
•  Clinical Applications
–  Vocal aging
•  Increased for children and elderly
–  Neurological pathology
•  Parkinson’s Disease
•  Amyotrophic Lateral Sclerosis
•  Laryngeal Cancer
–  Increased vocal fold mass (e.g., nodule, polyp, etc.)
–  Stuttering in young children (shimmer)
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Vocal Registers
• 
• 
• 
• 
Pulse
Modal
Midvoice
Falsetto
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Pulse
• Vocal frequency is 30 to 80 Hz in males and 90 to
165 Hz in females.
•  VFs are closed about 90% or time and open 10%.
•  Perceived as burst of acoustic energy but with
silence gaps.
•  Normal at end of phrases and sentences.
•  Clinical problem if used habitually.
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Modal and Midvoice
•  Modal
–  About 100 to 150 Hz in males
–  About 175 to 300 Hz in females
–  Perceived as normal speech
•  Midvoice
–  About 200 to 300 Hz in males
–  About 350 to 600 Hz in females
–  Often used in singing situation
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Falsetto
•  Vocal frequency of about 350 to 500 Hz in
males.
•  About 650 to 1000 Hz in females.
•  Vocal folds may not meet in middle because
of abnormal tension and may be breathy
•  “Reedy sound” due to widely spaced
harmonics.
•  Falsetto’s are not a part of normal speech.
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Summary
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