Physiological Processes of Speech production--reading Notes (4)

Vocal Fold and its oscillation

the larynx includes several structures such as the Subglottic Dome, vocal folds, ventricles, vestibular folds, epiglottis, and aryepiglottic folds, as shown In Fig.4a. the vocal folds Run Anteroposteriorly from the vocal processes of the arytenoid cartilages to the internal surface of the thyroid Cartila Ge. The vocal fold tissue consists of the thyroarytenoid muscle, vocal ligament, lamina propria, and mucous membrane . They form a special layer structure that yields to aerodynamic forces to oscillate, which is often described as The body-cover  structure

During voiced speech sounds, the vocal folds is set into vibration by pressurized air passing through the membranous portion of the narrowed glottis. The glottal airflow thus generated induces wave-like motionOf the vocal fold membrane, which appears to propagate from the bottom to the top of the vocal fold edges. When this oscillatory motion builds up, the vocal fold membranes on either side come Ng in repetitive closing and opening of the glottis. Figure4B shows that vocal fold vibration repeats four phases within a cycle:the closed phase, opening phase, open phase, an D closing phase. The conditions that determine vocal fold vibration is
The stiffness and mass of the vocal folds, the width of the glottis, and the pressure difference across the glottis.

The aerodynamic parameters that regulate vocal fold vibration is the transglottal pressure difference and glottal air Flow. The former coincides with the measure of subglottal pressure during mid and low vowels, which are about 5–10 cm H2O in COMF Ortable Loudness and pitch (1 cm H2O = 0. 98 hPa). The latter also coincides with the average measure of oralAirflow during vowel production, which is roughly 0.1–0.0./S. These values show a large individual variation:the pressure range is 4.2–9.6 cm H2O in males and 4.4–7.6 cm H2O in females, while the airflow rate ranges between 0.1–0.3 L/s in males and 0.09–0.L/s in females.

Figure 4a,b:vocal folds and their vibration pattern. (a) coronal sectionof the larynx,

Showing the tissues of the vocal and vestibular (false) folds. The cavity of the larynx

includes supraglottic and subglottic regions. (b) vocal-fold vibration pattern and

Glottal shapes in open phases. As the vocal-fold edge deforms in a glottal cycle,

< Span style= "Color:rgb (92,52,0)" >the glottis follows four phases:closed, opening, open and closing

figure 5shows schematically the relationship between the glottal cycle and volumic airflow change in Normal and breathy phonation. The airflow Varies within each glottal cycle, reflecting the cyclic variation of the glottal area and subglottal pres Sure. The glottal area curve roughly shows a triangular pattern, while the airflow curve shows a skew of the peak TO&N Bsp;the right due to the inertia of the air mass within The glottis

as shown in Fig. 5a. When the glottal closure Is more abrupt, the output sounds is more intense with richer harmonic components glottal , the airflow includes a direct-current  (DC) component and exhibits a gradual Decrease Of airflow, which results in a more sinusoidal waveform and a lower intensity of the output sounds, as Shown in fig.5b.

laryngeal control of the oscillatory patterns of the vocal folds is one of the major factors in voice qualitycontrol. In sharp voice, the open phase of the glottal cycle becomes shorter, while in soft voice, the open phase becomes longer. The ratio of the open phase within a glottal cycle is called theOpen quotient (OQ), and the ratio of the closing slope to the opening slope in the glottal cycle are called the speed quotient (SQ). These parameters determine the slope of the spectral envelope. When the open phase are longer ( highoq < Span style= "font-size:14px") with a longer closing phase (LowSQ", the glottal airflow becomes more sinusoidal, with weak harmonic components. Contrarily, when The Open phase is shorter (Lowoq

The oscillation of the vocal folds during natural speech is quasiperiodic, and cycle-to-cycle variation are observed I n speech waveforms as, types of measures:jitter (frequency perturbation) and shimmer (Amplitude Pertu rbation). These irregularities appear to arise from combinations of biomechanical (vocal fold asymmetry), neurogenic (involuntary AC Tivities of laryngeal muscles), and aerodynamic (fluctuations of airflow and subglottal pressure) factors. In sustained phonation of normal voice, the jitter are about 1% in frequency, and the shimmer are about 6% in amplitude.

Figure 5a,b:changes in glottal area and airflow in relation to output sounds during

< Span style= "Color:rgb (20,19,20)" >1.5 glottal cycles From glottal opening, with glottal shapes at peak opening (in the  /span>

< Span style= "Color:rgb (20,19,20)" >circles). (a) in modal phonation with complete glottal closure in the closed phase,  span>

< Span style= "Color:rgb (20,19,20)" >glottal closure causes abrupt shut-off of glottal airflow and strong excitation of the 

< Span style= "Color:rgb (20,19,20)" >air in the vocal tract during the closed phase. (b) In breathy Phonation, the glottal 

< Span style= "Color:rgb (20,19,20)" > closure is incomplete, and the airflow wave includes a DC component, which results 

In weak excitation of the tract

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Physiological Processes of Speech production--reading Notes (4)