1. Laryngeal Mechanics: Phonation, Frequency, Intensity and Vocal Register Control Lecture 2

2. VF Vibration
1) VFs abduct via PCA muscles during inhalation 2) VFs adduct via LCA, IA, TA muscles 3) Subglottal air pressure (Ps) builds beneath VFs 4) The Ps over comes the closed VFs and the folds are blown open 5) VFs open at bottom first; then the opening proceeds to top the of VFs 6) As top of VFs open, the bottom of the VFs begin to close creating a vertical phase difference 7) As the VFs vibrate, a wave-like motion in the cover of the VFs called the MUCOSAL WAVE occurs. The mucosal wave is an apparent sliding motion of the cover over the body of the VFs.
2. This slide summarizes the muscle activity involved in vocal fold vibration. For inhalation to occur, the VFs abduct via activity of the PCA muscles. For VF vibration to occur the VFs adduct via action of the LCA muscles which adduct the tips of the vocal processes (VPs)and membranous VFs, action of the IA muscle which adduct the AC and posterior glottis and action of the TA muscles which bulk and thicken the VFs and help with medial compression. Beneath the adducted VFs, subglottal pressure begins to build and eventually overcomes the closed VFs which are then blown open. The VFs open from bottom to top and then close from bottom to top creating a vertical phase difference. As the VFs vibrate, the vibration travels through the cover (a.k.a mucosa) of the VFs creating the mucosal wave which is an apparent sliding motion of the cover over the body of the vocal folds.

3. The Mucosal Wave
The VF ‘cover’ or ‘mucosa’ (epithelium and superficial lamina propria) appears to slide over the vocal fold ‘body’ (TA muscle) – it slides during vibration and produces a wave in the mucosa.
The wave appears to travel across the superior surface of the VFs about 1/3 to 2/3’s of the way from the lateral edge of the fold.
Alteration in the properties of the vocal fold ‘cover,’
such as scarring or stiffening by disease or surgical procedure, will affect normal vibration and diminish the wave.
3. Summary of the mucosal wave. Healthy VFs will exhibit a healthy mucosal wave that travels 1/3 to 2/3’s of the way from the lateral portion of the VFs. Any alteration in the properties of the VF cover, such as scar tissue or a lesion which causes increased stiffness, will alter the mucosal wave. VFs with increased stiffness due to vocal fold lesions, disease or surgeries resulting in VF scarring will show an decreased mucosal wave in the region of the lesion or scar area or across the entire VF.

4. Vocal Fold Vibration
4. Illustration of VF vibration.

5. Vocal Fold Vibration – Myoelastic Aerodynamic Theory of Phonation
‘Myoelastic’ refers to the laryngeal muscle activity that occurs during phonation and the effects of laryngeal muscle activity on the elasticity of VFs.
Aerodynamic refers to the aerodynamic determinants of the vibratory cycle, i.e., the opening and closing phases of vibration.
Two aerodynamic forces that are determinants
of VF vibration are :
1. Subglottal Pressure (Ps)
2. Negative pressure due to Bernoulli effect
5. You are all familiar with the Myoelastic Aerodynamic Theory of Phonation and the Bernoulli effect, but we will review these concepts before moving on to current theories of sustained VF vibration.
The prefix myo means muscle. Laryngeal muscle activity can effect VF elasticity. For example, CT activity increases VF stiffness and tension and decreases VF elasticity, while decreased CT activity or increased TA activity decreases VF stiffness and tension and increases VF elasticity because the VFs are relaxed and the mucosa is lax and pliable. Elasticity also refers to the elastic recoil that occurs after the VFs have been blown open. After the VFs have been blown open, the VFs recoil to the midline due to their mass and elasticity.
VF vibration would not occur w/o airflow and adequate Ps pressure. Thus an understanding of the aerodynamic determinants of VF vibration are important.
There are 2 primary aerodynamic determinants of VF vibration; the positive subglottal pressure that builds below the closed VFs that results in the open phase of vibration and the negative pressure that develops between the VFs due to the Bernoulli Effect which is aids in VF closure.

6. Subglottal Pressure (Ps) & Phonation
VFs adduct
Ps builds below VFs – Ps is the ‘opening force’
Membranous VFs open, a puff of air escapes & the glottis closes abruptly afterwards.
One puff follows another & an audible air pressure wave is set up at glottis & in the VT
For vibration to occur, pressure must be greater below the VFs than above.
Average Ps for conversational speech is 7-10 cm H2O
6. This slide summarizes the role of subglottal pressure in the phonatory process. Ps pressure is 7 – 10 cm/H2O for normal intensity speech. For louder phonation, Ps can be as high as 20 cm/H2O or as high as 50 cm/H2O during loud phonation in trained singers.

7. Aerodynamic Determinants of VF Vibration
Opening phase is due to build up of Ps
2) Closing phase is result of
a) the elasticity and mass of the VFs which moves VFs back to midline (closed) position
b) the Bernoulli Effect – a negative pressure
between the VFs.
7. While the opening phase is due to the build up of Ps, the closing phase is due to the natural elasticity and mass of the VFs

8. Principles of the Bernoulli Effect
When a gas/liquid flows thru a constricted passage, the velocity increases while the outward pressure of the molecules of the gas decreases
The pressure drop is perpendicular to the direction of the flow
If the walls are pliable, the decrease in the outward pressure of the flowing gas molecules moves the walls toward each other
8. The Bernoulli Effect is a physical principle that states that when a gas/liquid flows from a larger passage into a constricted or narrower passage, the velocity of the gas/liquid molecules must increase while the outward pressure of the molecules on the walls of the narrow passage decreases. This pressure drop is perpendicular to the direction of the flow. If the walls are pliable, as in the case of the VFs, the decreased outward pressure of the molecules pulls the walls toward each other.

9. Bernoulli Effect and the VFs
Subglottal pressure forces VFs apart
The narrow space that’s created in the glottis causes velocity of the air molecules to incr as they pass through the glottis
The increase in air molecule velocity results in a decrease in pressure between VFs
The decrease in pressure causes the walls of the glottis (VFs) to come together, along w/the natural elastic recoil of the VFs, this closes the VFs
9. This slide summarizes the role of the Bernoulli Effect in VF vibration.

10. Bernoulli Effect Decreased Ps between VFs due to Bernoulli Effect
VFs recoiling; move inward; glottal space becomes narrower
10. When the VFs are closed, subglottal pressure increases below the VFs until the pressure overcomes the closed VFs and the VFs open. The narrow passage created by the opening VFs causes the velocity of the air particles to increase as they move through the narrow passage. The perpendicular pressure exerted on the medial edges of the VFS (the walls of the glottis) then decreases and the walls of the VFs move inward toward the midline and assist with VF closure.
Positive Ps below glottis

11. Phonation Threshold Pressure (PTP)
PTP :minimum amount of subglottal pressure required to initiate VF vibration
PTP is affected by:
1) VF tension – PTP is higher for higher pitches
2) VF Viscosity – Greater viscosity = increased PTP
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. Water has low viscosity while honey has a higher viscosity.
3) VF thickness – Greater thickness = decreased phonation PTP (VFs are less stiff)
PTP – 0.1 to 1.0 kPa or cm H2O
11. There is a minimum amount of Ps that is required to initiate VF vibration. This is called ‘phonation threshold pressure ‘ (PTP) and is the minimum amount of pressure to just get the VFs oscillating (vibrating). PTP is affected by VF tension, stiffness and viscosity. Tension and stiffness will cause PTP to be greater because VFs that are stiff or tense require greater air pressure to initiate vibration. This occurs at high pitches due to the increased longitudinal tension in the VFs and when there is increased stiffness due to a VF lesion or scar tissue. VFs that are viscous also require greater air pressure to initiate vibration. Finally, VF thickness also affects PTP. VFs that are thicker are more lax and less stiff and thus require less air pressure to initiate vibration. PTP for phonation at a comfortable pitch and loudness is 1 – 10 cm/H2O.

12. Vocal Tract Inertance: The One Mass Model and Sustained Oscillation
Supraglottic area – area of vocal tract input pressure
Definition of inertia :
A property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force. 
12. Research by Ingo Titze (1988;1995) has shown that while the Bernoulli Effect and the Myoelastic-Aerodynamic Theory of Phonation adequately explain one cycle of VF vibration, these physical principles and theories do not explain ‘self-sustained’ VF vibration. How do the VFs continue to vibrate and sustain vibration ? We will address this question in a discussion of Vocal Tract Inertance or the One Mass Model of Vibration. This is important because many of our current therapy techniques result in or may result in an inertive vocal tract which helps the VFs vibrate more easily and with less effort (Titze,1997;2001;2004;2006;2008). Note that in this slide, there are three areas of pressure; pressure below the VFs (subglottal pressure; Ps), pressure between the VFs (transglottic pressure; P) and pressure above the VFs (supraglottic pressure; P1). The speckled area in the supraglottic area represents a sluggish, inertive vocal tract column air. It is the presence of the Vocal Tract which greatly helps us maintain sustained vocal fold vibration.
Air flow and air pressure are NOT the same things. Flow by definition is the quantity of a gas or fluid which passes a point in unit time.  In equation form, F = Q/t where F is equal to the mean flow, Q = the quantity (mass or volume) and T = time. Pressure is the ratio of force to the area over which that force is distributed. Pressure is force per unit area applied in a direction perpendicular to the surface of an object. Be sure you do not confuse air flow with air pressure. They are 2 different things.

13. Sluggish , inertive column of air in vocal tract
VFs opening P+
Faster moving air coming through the VFs
Area of positive supraglottic pressure
Airflow
Positive transglottal pressure which opens the VFs
13. The VFs open due to increased subglottal pressure. When this occurs, the rapidly moving air flow through the VFs runs into the sluggish, inertive slow moving air column in the vocal tract. The fast moving air ‘bumps’ into the sluggish column air in the vocal tract and this causes an area of positive pressure above the vocal folds in the supraglottic area that helps to drive the VFs further apart during the opening phase of vibration.

14. Accelerated, faster moving column of air in vocal tract
Negative supraglottal pressure ABOVE the VFs P-
Slower moving air between the VFs P-
Negative transglottal pressure between the VFs due to Bernoulli Effect
14. Eventually, the inertive, sluggish flow of air in the vocal tract begins move and accelerate. However, as the VFs begin to close, the transglottal pressure begins to decrease due to the increased narrowing of the glottis and the resultant Bernoulli Effect. When this happens, the air flow through the VFs begins to slow down and can not longer keep up with the accelerated air flow in the vocal tract. This causes an area of negative pressure in the supraglottic area just above the VFs. This area of negative supraglottic pressure helps the VFs close. If you’ve ever been on the freeway and have been passed by a large truck moving faster than your car and felt your car being pulled toward that truck then you have experienced the force of negative pressure. In this case, the supraglottic air flow is traveling fast but just below it the glottal air flow is slowing down so this causes an area of negative pressure just above the VFs which helps them close.
The VFs Closing

15. One Mass Model of VF Vibration: VT Inertance
Sustained vocal fold vibration is driven partly by transglottal pressure & partly by VT input or ‘supraglottic’ pressure
Ps increases , the VFs open, glottal airflow increases but the air column in VT is at first inertive, i.e. ‘sluggish.’ The air column does not want to move. Pressure then builds between & above VFs. This creates a positive P at input of the VT (above VFs) & further drives the VFs apart.
When glottis closes, the forward momentum and acceleration of the VT air column continues, but air flow thru glottis cannot keep up. This creates a suction, a negative pressure above VFs, which further closes the glottis.
15. Summary slide

16. Said yet another way……
When glottis is opening, vocal tract input pressure is positive and rate of change of flow is positive; flow increases.
This helps drive VFs apart.
When glottis is closing, vocal tract input pressure is negative, transglottal airflow is decreasing and rate of airflow change is negative. This makes VT input pressure negative and pulls VFs together.
Thus VF vibration is assisted in both directions, opening and closing, by changes in supraglottal pressure
The build up & release of supraglottic pressure is delayed in respect to opening and closing of VFs – this creates Vocal Tract Inertance
There is an asymmetry between driving force (pressure and flow) and the tissue velocity (opening and closing of VFs) due to the presence of Vocal Tract and this helps us maintain self sustained vibration.
16. Why is vocal tract inertance so important ? The greater the inertance, the easier it is for the VFs to vibrate and less laryngeal muscle activity is needed. VT inertance is increased whenever the VT is lengthened or narrowed.

17. Nonlinear Tissue Movement (3 mass model) & Sustained Oscillation (Titze 1980;1988;1995;2002)
Body (TA muscle)
Mucosa or Cover
17. The 3 mass model of VF vibration shown here models the VF structure with masses and springs. Here, ‘m1’ and ‘m2’ represent the top and bottom portions of the VF mucosa or cover and ‘m’ represents the VF body or TA muscle. The mucosa is represented as m1 and m2 because the top and bottom portions of the mucosa move out of phase. Recall that the bottom of the VFs opens first and then the top resulting in a vertical phase difference.

18. Airflow Nonlinear Tissue Movement opening closing
18. As the VFs open, the air molecules are converging, the transglottal pressure is positive and the net VF tissue velocity is outward due to positive pressure and increased air flow. As the VFs close, the air molecules are diverging, transglottal pressure is negative and the net VF tissue velocity is inward due to the negative transglottal and supraglottal pressures and the elastic recoil of the VFs. In both cases, energy from the air stream and air pressure is transferred to the VF tissue and the driving forces (airflow and pressure) are synchronized with VF movement; positive pressure and increased flow as the VFs open and negative pressure and decreasing flow as the VFs recoil. The fact that VF closure requires the opposite of VF opening results in the description of the closing or ‘restoring’ forces of the vibratory system as ‘asymmetrical.’ This asymmetry is an essential feature of self sustained oscillation.

19. Nonuniform Tissue Movement
Convergent glottis – VFs are opening from bottom to top, tranglottal pressure is positive, net tissue velocity is outward, and air molecules converge.
Divergent glottis – VFs are closing bottom to top, transglottal pressure is negative, net tissue velocity is inward, and air molecules diverge
Energy is transferred from air stream to the VF tissue because the net driving force (pressure) over the vibratory cycle is synchronized w/ the VF tissue movement.
Asymmetry in the restoring force of system is the essential feature of self sustained oscillation
19. Summary slide. Note that it is the asymmetry in the air pressure (positive for VF opening and negative for VF closing) that are essential for self sustained vibration.

20. What type of sound is generated by the Vocal Folds?
VF vibration generates a ‘quasi-periodic’ complex tone
Periodic – a sound wave that repeats itself EXACTLY the same way for each cycle of vibration.
Complex tone – a sound with more than one frequency; example, the vocal folds, a guitar string etc.
Sine wave (pure tone) – a sound with one and only one frequency; example, a tuning fork
20. The information on this slide should have been covered in your Speech Science course. A periodic sound wave repeats itself exactly for each cycle of vibration. Examples of periodic waves are those generated by the VFs, guitar strings, etc. A non-periodic sound wave is not the same cycle to cycle. Examples of non-periodic waves are noise, for example, the frication noise generated by the production of / s / or / θ / or shaking a bag of pennies. A complex tone is a tone with more than one frequency and consists of the fundamental frequency and its harmonics. A Sine wave or pure tone, consists of only one frequency. Some examples of complex tones or waves are VF vibration, vibrating strings of stringed instruments and the vibrating reeds of saxophones or clarinets

21. What type of sound is generated by the Vocal Folds?
The complex tone produced by vocal fold vibration consists of:
1) A fundamental frequency and its
2) Harmonics
Harmonics: whole number multiples of the fundamental frequency
Fundamental frequency: the lowest frequency in the complex tone. This will be the frequency of VF vibration.
21. The fundamental frequency of a complex tone is the lowest frequency in the tone. It’s the tone you hear. For example, if I speak or sing a tone at 200 Hz (G3), 200 Hz is the fundamental frequency. Harmonics are whole number multiples of the fundamental frequency. So, 200 x 1 = 200 Hz and that’s the first harmonic or H1, but it’s also the fundamental frequency. 200 x 2 = 400 Hz and this is the 2nd harmonic or H2. The 3rd harmonic is H3 and is 200 x 3 = 600 Hz and so on. Harmonics are infinite !

22. Sine Wave – tuning fork Complex Wave – Vocal fold vibration
22. Wave form examples of a pure tone or sine wave and a complex wave. The many in peaks in the complex wave represent the harmonics of the complex tone.
Complex Wave –
Vocal fold vibration

23. Spectrum of Glottal Source
VF vibration is quasi-periodic and is a complex tone
There is a fundamental frequency and numerous harmonics
Amplitude of harmonics decreases 12 dB per octave
23. VF vibration is actually ‘quasi-periodic.’ This means that there is some, although very slight, variation or ‘irregularity’ in the vibratory characteristics of VF vibration. This slide shows the frequency spectrum of the glottal source (VF vibration). The graph shows the fundamental frequency, which in this example is 100 Hz, and the harmonics. If we were to place an excised larynx on an airflow source, and thus have no vocal tract, the harmonics would decrease in intensity (energy) by 12 dB for every octave. This is true for our speaking or ‘modal’ register. For falsetto register, the decrease is dB per octave. Remember that an octave is defined as a doubling of frequency, i.e. 200 Hz – 400 Hz is one octave, 200 Hz – 800 Hz is 2 octaves, etc. With the vocal tract, particular harmonics get either amplified or attenuated depending on VT shape. Do you remember vowel formants ? Vowel formants are harmonics that are amplified because they are close to the resonant frequencies of the vocal tract. The resonant frequencies of the vocal tract depend entirely on VT shape which is different for every vowel sound.

24. Frequency
Frequency of VF vibration is determined by VF mass/thickness, length/tension, and elasticity.
Men have longer VFs, mm and women have shorter VFs mm
At rest, the longer the VF, and the > mass & thickness, the lower the fundamental frequency
Average fundamental frequency for men is 125 Hz and for women 225Hz
Frequency range for non-singers 1 – 1 ½ octaves
Fundamental frequency for speech is an individual’s average speaking pitch
24. The frequency of VF vibration is dependent upon VF length/tension, mass/thickness and elasticity. Men typically have longer vocal folds (at rest…so w/ no tension or lengthening) and thus have a lower fundamental frequency than women. If you’ve ever seen the inside of a piano, you may have noticed that the strings that produce the low frequencies are very long compared to the strings that produce the high frequencies which are very short. While there are average male and female fundamental frequencies, be aware that there is a range of normal. For example, the typical range of normal fundamental frequencies for the female voice is 175 Hz – 265 Hz and for men 90 Hz – 169 Hz. This varies a bit depending on the study you reference, but they’re all pretty close. Also be aware that even if your patient’s fundamental frequency is within the normal range, they may still be speaking too low or too high for their voice type. More on this later. Frequency ranges for non-singers are 1 to 1 ½ octaves. For singers, anything less than 2 octaves would be unusual.

25. Increasing Frequency of Vibration
Given a particular pair of VFs of a given length and mass, a person can increase the frequency of vibration by lengthening and tensing the vocal folds
Longer VFs do not result in decreased frequency in this case because the lengthening increases VF tension and decreases the effective mass of the VFs
25. Summary slide.

26. Increasing frequency Cricothyroid muscles contract
Cricoid and thyroid cartilages move towards each other, while thyroid & arytenoid cartilages move further apart
Posterior part of cricoid moves backwards while thyroid cartilage tilts down
VFs are lengthened
Lengthening of VFs increases longitudinal tension which results in increased frequency.
26. This slide provides you with a summary of the primary mechanism used to increase frequency which is activation of the CT muscle.

27. Possible Movements via Articulation of Thyroid and Cricoid Cartilages
27. This slide shows you the to possible movements of the TC as a result of CT muscle activity. The TC can rotate (on left) or translate (on right). In either case, the VFs will lengthen, VF tension will increase and frequency will increase.

28. Extrinsic Muscles and Frequency
Lowering frequency – sternohyoid , maybe sternothyroid
Raising Frequency – suprahyoids
Increases/decreases in vertical tension in conus elasticus which is continuous w/vocal ligament
28. While there is some research that shows that the extrinsic muscles may affect frequency of VF vibration, the effects are truly tertiary and not at all the primary mechanisms for frequency control. The infrahyoid muscles may contribute to frequency lowering by decreasing the tension in the conus elasticus and the vocal ligament. The suprahyoids may contribute to frequency increases by increasing the tension in the conus elasticus and vocal ligament. It is more likely, however, that the extrinsic laryngeal muscles contribute to laryngeal stabilization during the production of high frequencies. There are a number of studies that show increased strap muscle activity in singers during high pitch phonation.

29. Controlling Frequency
Longitudinal tension of VFs is altered by cricothyroid activity. Increased CT activity = elongation of VFs = increased VF longitudinal tension = increased pitch
Elevation/depression of larynx by extrinsic muscles has an effect on conus elasticus. Elevation can increase frequency while lowering can decrease frequency
Contraction of thyroarytenoid –can either increase or decrease frequency
Increasing subglottal pressure can increase frequency
29. This slide is a summary of frequency control mechanisms. We will now discuss 1) how the TA muscle can either decrease or increase frequency and 2) how subglottal pressure contributes to increases in frequency.

30. Body – Cover Models of Frequency Control (Fujimura, 1981; Titze, 1988)
Discusses 2 mechanisms for frequency control:
1) The Cover Model – Explains the effect of CT and TA muscle activity on the tension and stress of the VF cover.
2) The Body Cover Model – Explains how activity of the TA muscle can either increase or decrease frequency depending on the depth of VF vibration and level of activity in the CT muscle.
30. Ingo Titze (1988) has stated that there are 2 models of frequency control, the Cover Model and the Body-Cover Model. The Cover model predominates during low intensity (soft) speech or falsetto singing. The Body-Cover Model predominates during normal to high intensity speech or chest and head singing.

31. The Cover Model:
At low intensity (soft) speech or in falsetto singing, only the VF cover is in vibration.
When CT contracts, the VFs lengthen, longitudinal tension in the VF cover increases and frequency increases.
Fo= 1/ 2Lm√ σc/ρ
Where Lm = length of membranous VFs, σ = stress in the VF cover, and ρ is density of the tissue
If TA contracts in this condition, pitch will lower because the VFs will shorten and the cover will become loose and lax due to the decrease in tension/stress.
31. The Cover Model controls frequency during low intensity speech or falsetto singing. During low intensity phonation only the cover of the vocal fold is in vibration. Thus, if CT contracts the VFs will lengthen and the tension in the cover will increase and frequency will increase. If TA contracts, frequency will decrease because VF length and tension in the cover will decrease.

32. Body-Cover Model :
During normal to high intensity speech or singing in chest or head register, BOTH the VF body and cover are in vibration.
High intensity (loud) phonation results in increased amplitude and depth of vibration and thus the TA muscle is likely involved in vibration.
If the TA contracts in this condition, the overall stiffness/tension of VFs will increase and frequency will increase as long as CT muscle activity is not at its maximum.
If CT activity is at maximum then the frequency will decrease because contraction of TA in this case will shorten the vocal folds and the resultant shortening will decrease the overall VF stiffness.
32. During normal to high intensity speech and singing, the amplitude of VF vibration is great and the depth of vibration exceeds the cover and likely also involves the TA muscle. So, both the cover and the body are vibrating. This has important implications regarding frequency control. Note that increased VF tension or stiffness results in increases in frequency. Increases in VF tension/stiffness can be accomplished in two ways, 1) by increasing VF length which increases VF tension, OR 2) by activating the TA muscle which, if TA is involved in vibration, will increase the overall VF stiffness and increase pitch. Remember when a muscle is activated, it contracts and becomes stiffer.

33. Body – Cover Model of Pitch Control
BODY MODEL
33. Do not panic ! You are not required to memorize this equation. But, notice that there are 2 equations within the one equation; the Cover equation you saw earlier and now the Body equation. Note that the cover equation shows Lm which is membranous VF length and σp which is passive stress and ρ which is density. This indicates that frequency control during low intensity speech and falsetto are dependent upon the lengthening of the VFs and the resultant passive stress from the lengthening.
Notice that the Body equation has additional parameters. Here, da/d is ratio of the depth of vibration of the TA muscle (da) in relationship to total depth of VF vibration (d) and σam/σp is the maximum active stress the TA can generate divided by passive stress of all the VF tissue in vibration and ata = TA muscle activity. The take home point is that during normal and high intensity (loud) speech and chest and head singing, frequency control is dependent upon both the longitudinal tension resulting from VF lengthening via CT activity AND the increased overall VF tension/stiffness caused by TA activity. The role of the TA muscle in increasing VF stiffness and frequency of vibration is only possible because the amplitude of vibration is great/deep enough such that the TA muscles are vibrating.

34. Muscle Activation Plot (Titze, 2000)
34. This graph is called a muscle activation plot and shows the percent of maximum TA muscle activity on the x axis and percent of maximum CT muscle activity on the y axis. The curved bars represent different levels of lung pressure (Ps) by frequency. Look at the bar for 200 Hz. Notice that this frequency can be produced using many different combinations (levels) of CT and TA muscle activity and lung pressures depending on the level of intensity and vocal register used to produce that frequency. We will get to vocal registers shortly. So, frequency control, is more complex than you’ve previously been taught.

35. Relationship between Subglottal Pressure and Frequency (Titze, 1989)
To increase intensity, one must increase Ps, and often, frequency will increase as well. WHY?
Increased intensity = increased amplitude of vibration which causes the VFs to lengthen thus increasing VF tension which increases frequency.
This is called ‘dynamic strain’
Singers: learn to decrease CT or TA muscle activity while increasing subglottal pressure to increase intensity when they desire an increase in intensity w/out an increase in frequency.
35. Subglottal pressure has a role in frequency control. During high intensity phonation, the amplitude of vibration is great resulting in curved VFs. The curving lengthens the VFs and can cause an increase in frequency if CT and TA muscle activity is not modified to compensate for the effects of increased subglottal pressure and increased amplitude of vibration. The VF lengthening that results from the increased amplitude of vibration is termed ‘dynamic strain.’

36. Dynamic Strain Figure 1 – VFs at rest2 3
Figure 1 – VFs at rest
Figure 2 – CT activated; VFs lengthen; Can occur w/ and w/o vibration
Figure 3 – During vibration; VFs are blown apart; VFs curve; the
> ‘er the amplitude of vibration the >’er the curve of the VFs
Amplitude to length ratio – dynamic strain, ratio of curved VF fibers to straight fibers; longer fibers = increased pitch
36. These illustrations show VF length at rest, during CT muscle activation at rest and during phonation. The line indicates VF length. Figure 1 shows VF rest length. If we think of producing a medium to high pitch – try this, put your hand on your larynx and prepare to produce a high pitch – our larynx automatically elevates and, if we could see our VFs, we would see that they elongate in readiness to produce the high pitch. This is shown in figure 2. Figure 3 shows VF lengthening as a result of dynamic strain. The dotted line represents VF static length, i.e. VFs are lengthened but not yet in vibration. The curved line represents the curving of the VFs due to the amplitude of vibration. Which do you think is longer, the dotted line or the curved line ? The curved line is longer ! Figure 3 shows the effects of increased amplitude of vibration on VF length. Titze (1989) states that increases in pitch due to dynamic strain are more likely during low to moderate pitch phonation when the VFs are more lax and the amplitude of vibration is typically greater. At high pitches, amplitude of vibration is typically less because the VFs are long, thin and tense.

37. Vocal Registers
Register: A series of frequencies that are perceptually similar in quality and are produced in the same physiological manner
Register transitions: A Sudden change in vocal timbre or mode of vibration. Can have their origin in either 1) a change in muscle activity that results in a change in mode of vocal fold vibration, OR, 2) possibly subglottic resonances interfering with VF vibration
37. There are three vocal registers that researchers generally agree on and these are the modal or chest register, glottal fry or pulse register and falsetto register. A register is defined as a series of frequencies that are perceived to be of similar vocal quality and produced in the same physiological manner. Singers and singing teachers often refer to other registers such as middle or mixed register, head register and whistle register. These registers are less well defined in the research literature but likely exist. However, our understanding of these registers at this time is poor. A register transition is a sudden change in vocal timbre or mode of VF vibration. The abrupt change from modal/chest to falsetto is a register transition that most people are familiar with and it sounds like this (demo). Register transitions are due to changes in muscle activity that result in changes in glottal configuration and mode of vocal fold vibration or to subglottal resonances that interfere with VF vibration.

38. Vocal Registers Modal or Chest Register Characteristics:
* Thicker vocal folds (rectangular glottis)
* Complete VF closure
* Closed phase of vibration is equal in duration
or longer than open phase
* Greater energy in the mid and upper frequency
harmonics
* Greater amplitude of vibration and mucosal
wave excursion
38. The register we speak in is called the modal or chest register. It’s characterized by thicker vocal folds, complete VF closure during vibration, fairly equal open and closed phases during vibration, greater intensity (energy) in the mid and upper frequency harmonics and greater amplitude of vibration and greater mucosal wave excursion. Singers also sing in this register, particularly in their lower and mid frequency ranges.

39. Vocal Registers
Falsetto – Used to produce the highest pitches in one’s frequency range.
Characteristics:
* Vocal folds appear elongated, thinner, & stiff
* Incomplete or bow-shaped glottal closure
* Open phase of vibration is longer than closed phase
* Only anterior 2/3’s of VFs vibrate
* Decreased energy in the mid & upper harmonics
* Decreased amplitude of vibration & lateral excursion
of the mucosal wave
* Greater air flow than chest
* Sometimes a breathy quality
39. The falsetto register is the register we use to produce our highest frequencies. It is also used in singing in many musical genres such as R & B, Country and Pop. It is characterized by thinner, longer, and stiffer vocal folds, a longer open phase, decreased energy in the mid and upper harmonics, decreased amplitude of vibration, decreased mucosal wave lateral excursion, greater airflow and a breathy, fluty quality.

40. Differences in VF Cross-sectional Shape and Thickness For Chest and Falsetto
40. Falsetto register typically has less TA muscle activity than modal register and typically more CT activity. In falsetto, the VFs are longer, evidence of greater CT activity. The illustration on the right shows a VF cross-section for modal and for falsetto. Note how the medial edge or the vocal fold is more rectangular in modal register than in falsetto. There is also less vertical phase difference in falsetto due to the thinner medial edge and decreased VF mass.
Titze, 2000

41. Vocal Registers Glottal Fry or Pulse – occurs at the low frequencies
about Hz
Characteristics:
* Tightly adducted but flaccid appearing VFs
* Very long closed phase
* A ‘double’ open phase followed by an extended closed phase (nearly 2/3 of vibratory cycle)
* Low air flow
41. The usage of glottal fry register has become quite pervasive in teens and women in their 20’s and 30’s. Glottal fry is ‘air stingy’ and does not project well. It’s characterized by tightly adducted but flaccid appearing VFs, a very long and predominant closed phase and an unusual vibratory pattern. The vibratory pattern for one cycle of glottal fry is two open phases followed by a long closed phase. Speaking in glottal fry for extended periods can fatigue the voice.

42. Rest inhalation Modal Voice Falsetto Whispering Sataloff,1998
42. This illustration shows the different vocal fold closure patterns for different registers, modes of phonation, inhalation and rest. Note the bowed glottal configuration for falsetto.
Whispering
Sataloff,1998

43. Three intensity control mechanisms:
1) Below the larynx – increased Ps
2) At the larynx – increased VF adduction
3) Above the larynx – VT adjustments
43. Intensity is controlled and modulated by adjustments made below the larynx, at the larynx and above the larynx.

44. Intensity Control
Below the larynx –Respiratory drive must be adequate in order to produce normal to high intensity phonation. High intensity phonation requires increased subglottal pressure. Increasing Ps requires a greater volume of air and increased VF adduction.
At the larynx – Increased VF adduction. Longer duration of the closed phase allows Ps to build and faster VF closure results in increased intensity. The faster the VFs close, the greater the transglottal pressure drop.
*The greater the transglottal pressure drop, the greater the intensity of the sound*
MFDR – Maximum Flow Declination Rate. This is how rapidly the air flow goes to ‘0’ at the moment of VF closure
Above the larynx – The vocal tract acts a as resonator. Any harmonic in the vicinity of a VT formant gets a boost in amplitude (greater intensity)
FYI – a doubling in frequency results in a 6 dB increase in intensity a the glottal source
44. Vocal intensity can be controlled in several ways. First, there must be adequate respiratory drive in order to increase vocal intensity, and second, there must be adequate subglottal pressure. These are mechanisms below the larynx that contribute to intensity control. In order to have adequate subglottal pressure one must take in enough air AND have adequate laryngeal valving so that subglottal pressure can build beneath the VFs. Thus, at the level of the larynx, one needs adequate VFs adduction. The VFs must also remain closed longer and close more rapidly to produce a loud voice. The faster the VFs close, the greater the transglottal pressure drop. The greater the pressure drop, the greater the vocal intensity. Maximum Flow Declination Rate (MFDR) is an aerodynamic measurement that can be taken during a voice evaluation which tells us how quickly the VFs are closing by showing us how rapidly the transglottal airflow goes to zero. Finally, we can enhance vocal intensity by shaping the vocal tract to enhance the mid and upper frequency harmonics. Smith et al. (2005) showed that a frontal tone focus, such as that targeted in Lessac Marsden Resonant Voice Therapy, increases the intensity of mid and upper frequency harmonics by 6-12 dB. This helps with vocal projection and reduces the need for increased laryngeal muscle activity during voice projection.

45. Five Parameters Used to Describe Voice Production
Quality: breathy, hoarse, raspy, gravelly, strangled, strained etc
Pitch – low, normal, high
Pitch is perceptual correlate to frequency
Loudness – soft, normal, loud
Loudness is perceptual correlate to intensity
Resonance – timber: dark, bright, throaty/back,
Nasal etc
Register – glottal fry, modal, falsetto
45. There are five parameters commonly used to describe vocal production; quality, pitch, loudness, resonance and register. Quality refers to descriptors such as breathy, rough, and hoarse etc. Resonance refers to the timbre of the voice which can be bright, dark, throaty, nasal, and twangy etc.

46. Five Primary Parameters Used to Describe Voice Production
Vocal Quality – Is determined by the periodicity of vocal fold vibration and degree of glottic closure.
Loudness – Is affected by degree of glottal closure
1) Intensity is related to amount of subglottic pressure. Subglottic pressure is related to the degree and duration of VF adduction. Thus, greater adduction and longer closed times result in a greater build up of Ps.
2) Intensity is also related to the degree of transglottal air pressure drop. The faster and more completely the VFs close, the greater the transglottal pressure drop.
Resonance – Is the result of vocal tract filtering on the
spectrum of the glottal source and is dependent on vocal tract shape.
46. Vocal quality is primarily determined by the periodicity of VF vibration and degree of glottal closure. For example, a patient with VF paresis which results in a variable, mild longitudinal gap during phonation may present with a mild, breathy vocal quality due to the incomplete VF closure and excess escaping air. Likewise, a patient with incomplete VF closure may have difficulty increasing vocal intensity due to the inability to adduct the VFs fully and build subglottal pressure. The periodicity or regularity of VF vibration may be affected by the presence of VF lesions, VF asymmetries in mass and stiffness, or neurological disorders. On the opposite end of the spectrum, a patient with muscle tension dysphonia may present with a pressed, strained vocal quality due to increased VF adduction. Resonance is the result of vocal tract filtering on the spectrum of the glottal source. To give a simple example, if a patient with dysarthria has weakness in the palatal muscles and difficulty elevating the palate, that patient will present with a nasal resonance (nasality).

47. What to Know
Laryngeal anatomy: cartilages, muscles, muscle functions, O and I for intrinsic and extrinsic laryngeal muscles, VF layers, BMZ.
Myoelastic –Aerodynamic theory, PTP, mucosal wave
Bernoulli Effect
Vocal Tract Inertance, Nonlinear Tissue Movement, Cover Model, Body Cover Model
Type of tone produced; fundamental frequency, harmonics, average Fo’s for men/women, frequency ranges, glottal spectrum
Mechanisms of frequency and intensity control
Registers
Perceptual Voice Parameters
47. For the exam you should be familiar with all of these topics.