lecture 3 articulatory phonetics

7/31/2019 Lecture 3 Articulatory Phonetics

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Lecture 3

Vocal Organs and ArticulatoryPhonetics


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Overview How is speech produced by humans?

Vocal organs Lungs and trachea (windpipe) Larynx (voicebox) Vocal tract

Speech generation Excitation and modulation

Articulatory phonetics Phonetic alphabets

Consonants: manner and place of articulation Vowels

Continuous speaking effects Phonology


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MRI movie of speech


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4Text copyright J. J. Ohala, Sept 2001, from Sharon Rose slide

Nasal Cavity

Pharynx

Vocal Folds (within the Larynx)vibrate to give pitch

Trachea

Lungs

Oral Cavity

The vocal organs

Vocal tract :modulates thewaveform fromthe larynx

Provide energyfor speechproduction


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Lungs and trachea Speech generation relies on compressed air being provided on

which to modulate different speech sounds

This compressed air is produced in the lungs and delivered to thevocal organs through the trachea to the larynx

Non-speech breathing normally consists of equal inhalation andexhalation periods occurring about 17 times per minute

When speaking, the physiological requirement of oxygenation of theblood must continue, so breathing tends to occur as short inhalationsand long exhalations as the expelled air is being used to generatespeech. ( egressive sounds)

It is possible to make ingressive sounds: we can all do a pulmonic ingressive uvular trill

a snore

The main effect the lungs have on the output speech is its loudness


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LarynxThe larynx is a continuation of the

trachea but contains a highly specialisedcartilage structure and associated muscles.

The most important parts of the larynx are:

The arytenoid cartilages are the main controllers of the vocal folds.

Breathing: vocal folds held openSwallowing: vocal folds closed.

The vocal folds stretch across the larynxand when closed, separate the larynx fromthe trachea. The opening made by the vocalfolds is known as the glottis.

2. The arytenoid cartilage

1. The vocal folds (cords)


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Vocal Fold Vibration I1. When air pressure below the closed vocal chords (sub-glottal pressure)

is high enough, the folds are forced open (1-5 on diagram).2. As flow increases between the folds, the pressure drops (the Venturi

effect), and the folds come together again (6-10 on diagram)

3. Back to step 1.


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Varying the tension on the vocal folds affects the rate at which they open

and close, and this in turn affects the frequency (pitch) of the resultingspeech signal.

The frequency of the pitch signal above is f = 1/T

Speech sounds produced in this way are known as voiced .

When the tension of the vocal chords is less, they become quite loose.When air is forced from the lungs the effect is now to create a turbulentairflow rather than pulses. This is known as unvoiced speech.

Pitch period,T

Vocal Fold Vibration II


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Unvoiced Sounds Whispering occurs when the vocal chords are moved close together

but with a small opening remaining Air passing through this from the lungs creates turbulent airflow with

the resulting excitation signal resembling wideband noise

Excitation signal

There are no regular pulses of air and so the excitation has nospecific pitch period

Speech sounds produced by this form of excitation are termedunvoiced . Examples are /s/ as in step and /f/ as in from


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Laryngograph

A laryngograph is an instrument for recording the movements of thevocal folds during speech A small high frequency signal (3 MHz) is transmitted across the larynx. As the vocal folds move, the conductance of this signal changes, and

this change is recovered by the laryngograph.

10


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Vocal TractThe vocal tract is normally considered to be everything past the

vocal folds.Vocal tract can be divided intofollowing regions :

1. Oral cavity

2. Nasal cavity

3. Pharynx

and contains anumber of articulators :

a. Tongueb. Soft palate (velum)c. Hard palated. Teethe. Alveolar ridgef. Lips


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The vocal tract can be considered to be a series of connected cavities,each with their own resonant frequencies.

The movement of the articulators (tongue, velum) changes thephysical shape of these cavities and hence the resonant properties of the vocal tract.

As the air from the larynx flows through the vocal tract, the resonantfrequencies of these cavities modulates different effects onto the air flow and creates different speech sounds.

The use of different components of the vocal tract has different effectson the produced speech signal.

Moving the tongue changes the shape of the oral cavity and hence itsresonant properties. The nasal cavity can also be closed off by thevelum.

Vocal Tract


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A model of speech generation

We have now considered the physical operation of the vocal organs.The operation of these for generating speech can be divided intoexcitation and modulation , with the lungs supplying the energy

Excitation is the process of taking the air flow from the lungs andbuilding from this a suitable flow of air which can be used as the inputto the modulation process

Modulation occurs in the vocal tract and is the process of using thearticulators to impart information onto the excitation signal

Air flow(lungs)

Modulation(vocal tract) Speech

Excitation(vocal cords)


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Modulation Modulation is the process of imposing information on the excitation, or

glottal, waveform

Considering the effect of modulation from a physiological point of viewis termed articulatory phonetics

While considering modulation in terms of its acoustic properties isknown as acoustic phonetics

Articulatory phonetics considers how changes in the vocal organschange the resulting speech sounds. These changes are mainlyeffected by the tongue, but also other components such as the velum,teeth and lips

Acoustic phonetics considers the modulation as a filtering operationapplied to the excitation waveform. The vocal tract can be thought of asan acoustic tube which has various resonant frequencies

These resonant frequencies can be adjusted by the articulators in thevocal tract and are known as formants


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Illustration of Speech Generation I Analysis of speech production mechanism shows that the resultant

speech output is determined by modulating the excitation signal bythe vocal tract.

Consider the stationary vowel sound at end of utterance three -voiced speech.

Frequency responseof vocal tract

Formants

F1 F2 F3 F4

Pitch period = 5.5ms,so pitch, F 0 = 181Hz

Excitation signal Speech signal

Excitation

(glottis)

Modulation

(vocal tract)Speech


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Illustration of Speech Generation IIConsider now an unvoiced sound: the /th/ sound at the start of the

utterance three.

Excitation consists of wideband noise - no pitch

Excitation signal Frequency responseof vocal tract

Much less formantstructure

Speech signal

Output speech alsonoise-like

Excitation(glottis)

Modulation(vocal tract) Speech


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Articulatory phonetics and phonology

Phonetics : relates to the anatomy and physics required tounderstand how different speech sounds are produced. This isindependent of any particular language

Phonology : study of the organisation of speech sounds in relation toa particular language ( phonology is to the speech sounds in alanguage as syntax is to the words of language)

Articulatory Phonetics : study of how speech sounds are produced inrelation to anatomical details. In particular the position of the vocalorgans when producing particular speech sounds

Acoustic Phonetics : study of observable and measurable

characteristics of speech sounds with particular focus on how todistinguish between different sounds. Provides importantbackground for speech recognition and synthesis


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Phonemes and phones A phoneme is an abstract signalling unit: if two speech sounds

differentiate two words, they are said to be different phonemes Consider pat and bat: the sounds at the start of these words

differentiate them in English, so they are different phonemes, writtenas /p/ and /b/.

In some languages, they might not be differentiated, so they would

not be phonemes. But they are still different sounds, and areregarded as phones rather than phonemes.

In Japanese, [r] and [l] are not distinct phonemes, so Japanesepeople find it difficult to recognise and pronounce these differences

A phoneme is actually a set of acoustically similar sounds which, for a

given language, are accepted as conveying the same meaning. Members of the same set are called allophones . Consider the

phoneme /k/ at the beginning of kin and cup. Both represent thesame phoneme, but sound slightly different.


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International Phonetic Alphabet (IPA)Examples of symbols and their associated sounds.


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SAMPA symbols for British English

p pear T thing

b bear D this

f fear U good

v very u boot

S sheer 3 bird

Z treasure ...

tS cheer Some symbols appear logical, others not so.

dZ jeer

@ ago Complete set available. See, for instance:

I bit

V bud

http://www.ims.uni-stuttgart.de/ projekte/mate/mdag/pd/

pd_2.htm


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Consonants and vowels

Now that we know how speech sounds are produced bythe vocal organs we will now examine specifically theproduction of consonants and vowels


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ConsonantsConsonants are relatively easy to define in anatomical

terms. They are principally distinguished by:

1. Place of articulation

2. Manner of articulation

3. Voicing or phonation


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Place of articulation

Name Description Example

1. Bilabial Between lips pea2. Labio-dental Lower lip to upper teeth fee3. Dental Front of tongue between teeth thigh4. Alveolar Front of tongue to alveolar ridge see5. Alveopalatal Front of tongue between

alveolar ridge hard palate she6. Palatal Middle of tongue to hard palate you7. Velar Root of tongue to rear of mouth key 8. Uvular Tongue to uvular French r (none in English)9. Pharyngeal Tongue to pharynx Arabic (none in English)10. Glottal Constriction at glottis sor of (Cockney)

This is the place in the vocal tractwhere the major source of constriction occurs

It is defined in terms of both theactive and the passive articulators


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Manner of articulationManner of articulation is characterised by the degree of constriction

and the manner of its release into the following sound.


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Voicing

Indicates presence or absence of phonation

Previous tables have shown that consonants can have voiced or unvoiced forms, depending on phonation

Examples is voiced zzz and unvoiced sss


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Vowels Vowels are less well defined than consonants. The tongue rarely

touches another organ in the vocal tract so gives no specific points of

articulation

Vowels can be roughly described in terms of their position in themouth by four variables:

1. Tongue high or low2. Tongue front or back

3. Lips rounded or unrounded4. Nasalised or unnasalisedConsidering only the position of the tongue, a vowel diagram can beused to show the location of different vowels.

High

Low

Middle

Front Back

iI

u

o

c

e e

High

Low

Middle

Front Back

had

heed

hid

whod

hoed

bud

hayeda head

head

hawed


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Vowels The vowels shown in the diagram are most common in English, but the diagram

is not entirely consistent.

Front vowels are pronounced with the lips unrounded (heed). Back vowels arepronounced with lips rounded (whod).

This is customary in English, but not in all languages. Leads to two voweldiagrams to accommodate the differences - one for rounded vowels and the other for unrounded vowels.

The neutral vowel [ ] is one of the most commonly used and is given the nameschwa . Examples of schwa are start of above and end of soda.

Velum determines whether a vowel is nasalised or unnasalised. When the velumis open this opens up the nasal cavity which can impart more structure onto thevowel sound.

In the English language, no distinction is made between nasal and unnasalisedvowels. However in some languages (for example French) the difference isimportant.


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Continuous speaking effects Useful to analyse speech generation using phonetics, but in reality, phones are

not produced accurately in the context of other phones.

Each phone can be considered a target at which the vocal organs aim, but inreality never actually reach. Typically, once the target has been approachedclose enough to be intelligible, the organs change their destination to the nextphone.

Coarticulation is the altering of phonemes as a result of their neighbouringsounds. For example I went by bus is typically spoken as I wemp by bus.

Changes are /n/ /m/ and /t/ /p/ because of the bilabial /b/ in by.

Some words change if following word begins with a vowel. e.g. the

the mouse and the elephant

Some words are shortened

you and me you an me

I must see you I ms ee you


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Summary Examined vocal organs used in speech generation - lungs/trachea,

larynx/vocal cords, vocal tract

Considered speech generation in terms of an excitation signal and itsmodulation by vocal tract

Looked at differences between voiced and unvoiced sounds

Articulatory phonetics - IPA alphabet of speech sounds

Vowels and consonants - position of articulators to produce thedifferent speech sounds

Continuous speaking effects and coarticulation

lecture 3 articulatory phonetics

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