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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 120 Hz• Females 220 Hz• Children 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