Vocal Fold Physiology + Voice Quality

October 9, 2014

Average Everydayness• Don’t forget to send me your second production exercises by Monday!

• Also: course project report #2 is due on Tuesday.

• Today:

• The Wonderful World of the Larynx!

Where Were We?• Air squeezed out of the lungs travels up the bronchi...

• Through the trachea (windpipe)

• To a complicated structure called the larynx.

• ...where phonation happens.

The Larynx• The larynx is a complex structure consisting of muscles, ligaments and three primary cartilages.

1. The Cricoid Cartilage• The cricoid cartilage sits on top of the trachea

• from Greek krikos “ring”

• It has “facets” which connect it to the thyroid and arytenoid cartilages.

cricoid cartilage

2. The Thyroid Cartilage• The thyroid cartilage sits on top of the cricoid cartilage.

• from the Greek thyreos “shield”

• The thyroid cartilage has horns!

• Both lower (inferior) and upper (superior) horns

• The lower horns connect with the cricoid cartilage at the cricoid’s lower facet.

• The upper horns connect to the hyoid bone.

Thyroid Graphic

thyroid cartilage

cricoid cartilage

Thyroid Angles• The two broad, flat front plates of the thyroid--the laminae--meet at the thyroid angle.

• The actual angle of the thyroid angle is more obtuse in women.

• ...so the “Adam’s Apple” juts out more in men.

3. The Arytenoid Cartilages• There are two arytenoid cartilages.

• from Greek arytaina, “ladle”

• They are small and pointy, and sit on top of the back side, or lamina, of the cricoid cartilage.

arytenoid cartilages

cricoid cartilage

The Vocal Folds• These three cartilages are connected by a variety of muscles and ligaments.

• The most important of these are the vocal folds.

• They live at the very top of the trachea, in between the cricoid and thyroid cartilages.

• The vocal folds are a combination of:

• The vocalis muscle

• The vocal ligament

• The vocal folds are enclosed in a membrane called the conus elasticus.

• Just above the true vocal folds are the “false” (!) vocal folds, or ventricular folds.

• The space between the vocal folds is the glottis.

Vocal Fold View #1

Vocal Fold View #2• The vocal ligaments attach in the front to the thyroid cartilage.

• ...and in the back to the arytenoid cartilages.

• The glottis consists of:

• the ligamental glottis

• the cartilaginous glottis

Things Start to Happen• Note that the arytenoid cartilages can be moved with respect to the cricoid cartilage in two ways.

#1: rocking #2: sliding

The Upshot• The arytenoids can thus be brought together towards the midline of the body.

• Or brought forwards, towards the front of the thyroid.

• The rocking motion thus abducts or adducts the glottis.

• The sliding motion shortens or lengthens the vocal folds.• Check out the arytenoids in action.

• When the vocal folds are abducted:

• air passes through the glottis unimpeded and voicelessness results.

• The posterior cricoarytenoid muscles are primarily responsible for separating the arytenoid cartilages.

• Voicing may occur when the vocal folds are adducted and air is flowing up through the trachea from the lungs.

• Two muscles are primarily responsible for adducting the vocal folds.

• The first is the lateral crico-arytenoid muscle.

• Note that the lateral cricoarytenoid muscles only adduct the ligamental glottis.

• The transverse arytenoid muscles pull together the arytenoid cartilages themselves.

• Thereby closing the cartilaginous glottis.

The Consequences• The combined forces drawing the vocal folds towards each other produce adductive tension in the glottis.

• Adductive tension is increased by:

• lateral cricoarytenoid muscles

• transverse arytenoid muscles

• Adductive tension is decreased by:

• posterior cricoarytenoid muscles

• Adduction vs. abduction determines whether or not voicing will occur.

• But we can do more than just adduce or abduce the vocal folds...

Controlling F0• Question: why do women have a higher F0 than men?

• A: Shorter vocal folds open and close more quickly.

• In men:

• Ligamental glottis 15.5 mm

• Cartilaginous glottis 7.5 mm

• Total glottis length 23 mm

• In women:

• Ligamental glottis 11.5 mm

• Cartilaginous glottis 5.5 mm

• Total glottis length 17 mm

Factor Two

• F0 also depends on the longitudinal tension in the vocal folds.

• I.e., tension along their length, between the thyroid and arytenoid cartilages.

• Higher tension = higher F0

• Lower tension = lower F0

• Q: How can we change longitudinal tension in the larynx?

• A: We can rotate the thyroid cartilage up and down on its connection with the cricoid cartilage.

• ...like the visor of a knight’s helmet.

• This either stretches or relaxes the vocal folds.

Contradictory?• No, just complicated. Note:

• Lengthening (stretching) the folds results in higher tension

• ...which results in higher F0

• Shortening the folds results in less tension

• ...which results in lower F0

• “Higher” and “lower” F0 have to be understood relative to the speaker’s normal F0 range.

• still lower for men

• still higher for women

For the Record• Contraction of the cricothyroid muscle pulls down the thyroid cartilage.

• Interestingly: researchers often study the activity of this muscle using EMG.

Fun Stuff (= tracheotomy)Peter Ladefoged: “To record the pressure of the air associated with stressed as opposed to unstressed syllables we need to record the pressure below the vocal folds. A true recording of the subglottal pressure can be made only by making a tracheal puncture.This is a procedure that must be performed by a physician. A local anesthetic is applied both externally and inside the trachea by means of a fine needle. A larger needle with an internal diameter of 2 mm can then be inserted between the rings of the trachea as shown in figure 3.3”

Figure 3.3

“As you can see from my face it is not at all painful. But it is not a procedure that can be carried out in fieldwork situations.”

For the Record, part 2• Longitudinal tension can also be reduced by the thyroarytenoid muscles.

• Which connect the thyroid to the arytenoid cartilages.

vocal folds

• These muscles are inaccessible to EMG

Check it out!• Let’s look at some pitch shifting laryngoscopy videos.

Factor #3• Increasing longitudinal tension also makes the vocal folds thinner.

• Thinner vocal folds open and close more quickly.

• Average thickness of male vocal folds =

• 2-5 mm

• Female folds are somewhat thinner

low F0

mid F0

high F0

Frequency and Vowels• In the mystery tone language exercise, you may have noticed that the fundamental frequency of [i] was slightly higher than that of [a], for the same tones

“Intrinsic” Pitch• It’s been observed that F0 is usually higher for high vowels than for low vowels

[i] 183 Hz

[e] 169

[æ] 162

[a] 163

[o] 170

[u] 182

• Data from Lehiste & Peterson (1961) for American English

• The “Tongue Pull” Hypothesis (Honda, 2004):

• Raising the tongue for high vowels also raises the larynx

• The cricoid cartilage rises up and around the spine…

• Thus stretching the vocal folds

• and increasing longitudinal tension.

An Intrinsic Summary High Vowels Low Vowels

Intensity Less More

Duration Shorter Longer

F0 Higher Lower

• A word of caution:

• All of these factors (intensity, duration, F0) factor into perceived prominence and stress.

Contact!• Interesting (and important) fact: the vocal folds do not open and close all at once.

• Their upper and lower parts open and close out of phase with each other.

Implications• Glottal opening and closing forms a complex wave.

• The out-of-phase factor is reduced with thinner vocal folds.

• i.e., the glottal cycle becomes more sinusoidal

Electroglottography• The degree of vocal fold separation during voicing can be measured with a method known as electroglottography (EGG)

• Electrodes are placed on either side of the larynx

• More contact between vocal folds greater conductivity between electrodes

• A caveat:

• tends to work better on men than women.

EGG Readout

EGG Output

“The north wind and the sun were disputing which was the stronger, when a traveler came along wrapped in a warm cloak.”

An EGG Schematic1. Complete closure of vocal folds

conductivity

An EGG Schematic2. Lower half of folds begin to open

conductivity

An EGG Schematic3. Upper half of folds open

conductivity

An EGG Schematic4. Folds are completely apart

conductivity

An EGG Schematic5. Lower half of folds begin to close

conductivity

An EGG Schematic6. Upper half of folds close

conductivity

An EGG Schematic7. Folds are completely closed, again

conductivity

An Actual EGG Waveform• Modal voicing (by me):

• Note: completely closed and completely open phases are both actually quite short.

• Also: closure slope is greater than opening slope.

• Q: Why might there be differences in slope?

Factor #5• There is another force at work: medial compression.

• i.e., how tightly the folds themselves are compressed against each other.

• Medial compression determines, to some extent, how quickly/slowly the folds will open.

MC Forces, yo• Medial compression is caused by constriction of:

1. The lateral cricoarytenoids

• which adduct the vocal folds

2. The thyroarytenoids

• which pull the arytenoids towards the thyroid

• But not the interarytenoids

• ...which only squeeze the arytenoid cartilages together

For the Record, part 3• It is not entirely clear what the role of the vocalis

muscle plays in all this.

• The vocalis muscle is inside the vocal folds

The Vocalis Muscle1. It may also shorten the vocal folds through contraction

• thereby potentially lowering longitudinal tension

• and lowering F0

2. However, the same contraction would increase medial compression within the vocal fold

• thereby decreasing vocal fold thickness

• and increasing F0

• Researchers still need to figure out a way to get at this muscle while it’s in action…

Vocal Fold Force Summary1. Adductive Tension

• between arytenoids + folds

2. Longitudinal Tension

• stretches vocal folds

3. Medial Compression

• squeezes vocal folds together

1. Modal Voice Settings• At the low end of a speaker’s F0 range:

1. Adductive tension force is moderate

2. Medial compression force is moderate

3. Vocal folds are short and thick.

• = longitudinal tension is low

4. Moderate airflow

• F0 is increased by:

1. Increasing the longitudinal tension

activity of the cricothyroid muscle

2. Increasing airflow

A Different Kind of Voicing• Tuvan throat singing (khoomei):

A Different Kind of Voicing• The basic voice quality in khoomei is called xorekteer.

• Notice any differences in the EGG waveforms?

• This voice quality requires greater medial compression of the vocal folds.

• ...and also greater airflow

• Check out the tense voice video.

Modal vs. Tense Voice• The language of Mpi contrasts modal voice vowels with tense voice vowels.

• Mpi is spoken in northern Thailand.