Voice Quality January 19, 2010

Vocal Tract Anatomy Our vocal tracts are shaped in a way that makes it easier to speak… But more dangerous to eat!

A Framework Rehash Last time, we found out that the larynx is built upon a framework of three different cartilages: 1.The thyroid cartilage 2.The cricoid cartilage 3.The arytenoid cartilage(s)

A Movement Rehash The cartilages are held together by a network of muscles and ligaments. The contraction of specific muscles can move the cartilages around with respect to each other. The arytenoid cartilages can exhibit two movements: 1. “Rocking” towards each other Either abducts or adducts the vocal folds 2.“Sliding” towards the thyroid The “rocking” motion induces adductive tension in the vocal folds.

We can also 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.

Two Factors F0 depends on the length of the vocal folds. (longer in men than in women) 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

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

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

For the Record Contraction of the cricothyroid muscle pulls down the thyroid cartilage. Interestingly: researchers often study the activity of this muscle using Electromyography (EMG).

Electromyography (EMG) When that muscle contracts, it discharges an electrical signal (an action potential). The voltage and timing of this discharge may be recorded through the electrode. In EMG, an electrode is inserted into a particular muscle.

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

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

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.

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: works 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 Schematic 1. Complete closure of vocal folds conductivityconductivity

An EGG Schematic 2. Lower half of folds begin to open conductivityconductivity

An EGG Schematic 3. Upper half of folds open conductivityconductivity

An EGG Schematic 4. Folds are completely apart conductivityconductivity

An EGG Schematic 5. Lower half of folds begin to close conductivityconductivity

An EGG Schematic 6. Upper half of folds close conductivityconductivity

An EGG Schematic 7. Folds are completely closed, again conductivityconductivity

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.

EGG Measures 1.Open quotient Percentage of each glottal cycle in which the glottis is completely open. 2.Slope How rapidly do the folds open/close? Is there a difference between opening and closing slopes? Why might there be differences in slope?

Factor #4 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 fold. 1.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

Vocalis Muscle

Vocal Fold Force Summary 1.Adductive Tension between arytenoids 2.Longitudinal Tension stretches vocal folds 3.Medial Compression squeezes vocal folds together

Modal Voice Settings At the low end of a speaker’s F0 range: 1. Adductive tension force is small 2. Medial compression force is small 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 Tuvan throat singing (khoomei): xorekteer voice Notice any differences in the EGG waveforms? This voice requires greater medial compression of the vocal folds....and also greater airflow

Taken to an Extreme Extreme medial compression can lead to the closure of the ventricular folds, as well as that of the true vocal folds. = ventricular voice The false and true vocal folds effectively combine as one. …and open and close together (usually) Kargyraa voice Head over to the video evidence.

Ventricular Voice EGG Notice any differences? Difference between closing and opening slope is huge! Also: amplitude is larger.

2. Creaky Voice A voice quality that is somewhat similar to ventricular voice is creaky voice. Also known as “glottal fry” Laryngeal settings for creaky voice: 1.Ventricular folds often compressed down on true vocal folds. 2.High medial compression 3.Very little longitudinal tension 4.Low airflow  Air bubbles up sporadically through the folds, near the thyroid arch.

Creaky EGG Note: vocal folds are very short during creaky voicing. Look at the creaky video.

Creaky Quirks Note: creaky voice often emerges at the low end of a speaker’s range. In a language like English: at the ends of utterances In a tone language: for very low tones. Note: creaky voice also often has a “double pulse” effect.

Modal to Creaky [][]

Jitter Creaky voice often exhibits a lot of jitter and shimmer. Jitter = Variation in timing of glottal pulses Defined as a percentage: period deviation/period duration.

Shimmer Shimmer = Variation in amplitude of glottal pulses Note: synthetic speech has to include jitter and shimmer …otherwise the voice won’t sound natural. Check the measures out in Praat.

3. Breathy Voice In breathy voice, the vocal folds remain open… and “wave” in the airflow coming up from the lungs. Laryngeal settings for breathy voice: 1.Low medial compression 2.Minimal adductive tension 3.Variable longitudinal tension (for F0 control) 4.Higher airflow Check out the breathy video.

Breathy Voice EGG Also note: closure phases in breathy voice are more symmetrical than in modal voice.

Contrasts Gujarati contrasts breathy voiced vowels with modal voiced vowels: Hausa contrasts modal [j] with creaky [j]: Hausa is spoken in West Africa (primarily in Nigeria) Creaky consonants are also said to be laryngealized.

All Three Jalapa Mazatec has a three-way contrast between modal, breathy and creaky voiced vowels: Jalapa Mazatec is spoken in southern Mexico, around Oaxaca and Veracruz.

One Random Thing Breathy voiced segments can “depress” the tone on a following segment. Examples from Tsonga: Tsonga is spoken in South Africa and Mozambique. Voiced stops also “depress” tones more than voiceless stops. depressor consonants Nobody really knows why.

Open Quotient From EGG measures, we can calculate the “open quotient” for any particular voicing cycle = time glottis is open period of voicing cycle EGG measures show that there are reliable differences in open quotient values between the three primary voicing types. Breathy voicing has a high open quotient Creaky voicing has a low open quotient Modal voicing is in between

Open Quotient Traces one period open phase The open quotient in modal voicing is generally around 0.5

Tense Voice Tense voice (from throat singing demo) has a lower open quotient. Result of medial compression. Actual value: about 0.3 one period open phase

OQ Traces, continued OQ for creaky voice is also supposed to be low… but it’s actually quite sporadic. Breathy voice OQ is quite high (0.65 or greater)