sppa 403 speech science1 unit 3 outline the vocal tract (vt) source-filter theory of speech...

SPPA 403 Speech Science 1

Unit 3 outline

• The Vocal Tract (VT)• Source-Filter Theory

of Speech Production• Capturing Speech

Dynamics• The Vowels• The Diphthongs• The Glides• The Liquids

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Source-Filter Theory: Modeling Vowels

Vowels are• Voiced (shapes the glottal source spectrum)• oral (velopharyngeal port closed)• produced with “open” vocal tract (VT)

– Poral ~ Patmos

• Classified according to tongue position in VT– front/central/back– high/mid/low

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Vowel Quadrilateral

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Source-Filter Theory: Modeling Vowels

• Mobile articulators serve to change the VT area function so that it is not constant

• non-constant area function complexity for determining VT transfer function

• However, VT transfer function still based on tube acoustics

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Artic. Config. Area Function Transfer Function

glottis lipsfrequency

gain

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Source-Filter Theory: Modeling Vowels

• VT has an infinite number of resonances/formants

• Identification of vowel quality seems most dependent upon the location of F1, F2 & F3

• These observations are based on – Studies of vowel perception– Modeling efforts which suggest F4-F6 are relatively

static– the observation that glottal source spectrum rolls off

with increasing frequency

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Mid Central vowelF1: 500 HzF2: 1500 HzF3: 2500 Hz

/i/

/u/

//

//

frequency

Am

plit

ude/

gain

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Tongue “Rules” for vowel formant values

/i/ & /u/ have a low F1

// & // have high F1

Tongue height ~ F1

Tongue height F1 Tongue height F1

/u/ & // have low F2

/i/ & // have high F2

Tongue A-P ~ F2

Tongue front F2 Tongue back F2

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Mid Central vowelF1: 500 HzF2: 1500 HzF3: 2500 Hz

/i/

/u/

//

//

frequency

gain

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Lip “Rules” for vowel formant values

Lip rounding (for /u/) ~ F2

Note* lip protrusion will increase the overall length of the vocal tract which will decrease all formant values

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Mid Central vowelF1: 500 HzF2: 1500 Hz

/i/

/u/

//

//

frequency

Am

plit

ude/

gain

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IMPORTANT

• Tongue and lip rules are based on how these articulations change the VT area function (shape)

• VT area function ultimately determines the VT filter properties

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Tf32 example

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F1-F2 values for English Vowels

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Vowels: Stylized Spectrograms

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Vowels: Stylized Spectrograms

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/a/ - low back ( F1 F2)

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/i/- high front ( F1 F2)

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/u/ - high back ( F1 F2)

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/ae/ - low front ( F1 F2)

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How important are F1-F3 in speech production & perception?

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Sinewave Speech Demonstration

Sinewave speech examples (from HINT sentence intelligibility test):

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Problem

• Recall - F1 = c/4l

• VT length influences exact frequency location of formants

• Speakers vary in their vocal tract length

• men > women > children

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Problem

/i/

/u/

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How do we know that a child, a man and a women all say /i/, when the acoustic values of formants are quite different?

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A possible answer??

F2

F1

children

women

men

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A possible answer??

• Relative locations of formants is similar across speakers even though absolute values differ

• Perhaps we ‘rescale’ our expectations depending upon factors such as gender and age

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Vowel articulation and vowel acoustics

• Vowel quadrilateral: articulatory plane

is similar to

• F1-F2 plot: acoustic plane

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SPPA 403 Speech Science 32back front

low

high

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Vowel articulation and vowel acoustics

• Vowel quadrilateral: articulatory plane

is similar to

• F1-F2 plot: acoustic plane

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Unit 3 outline

• The Vocal Tract (VT)• Source-Filter Theory

of Speech Production• Capturing Speech

Dynamics• The Vowels• The Diphthongs• The Glides• The Liquids

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Diphthongs

• Slow gliding movement between two vowel qualities

• characterized by an articulatory transition

• articulatory transition = formant transitions

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Diphthongs

• /ai/ - “bye”

• /au/ - “bough”

• /oi/ - “boy”

• /ei/ - “bay”

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Diphthongs: /ai/

a i

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Diphthongs: /au/

a u

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Unit 3 outline

• The Vocal Tract (VT)• Source-Filter Theory

of Speech Production• Capturing Speech

Dynamics• The Vowels• The Diphthongs• The Glides• The Liquids

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Glides (/w/, /j/) & Liquids (/l/, /r/)

• often termed sonorants

• Associated with – a high degree of vocal tract constriction– articulatory transition = formant transition

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Glides (/w/, /j/) & Liquids (/l/, /r/)

Degree of Constriction• Greater than vowels

– Poral slightly greater than Patmos

• Less than fricatives– Poral for glides/liquids < Poral for fricatives

• Constriction lasts ~ 100 msec• Constriction results in a loss in energy

– weaker formants

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Glides (/w/, /j/) & Liquids (/l/, /r/)

Transition rate

• faster than the diphthongs

• slower than the stops

• lasts ~ 75 msec

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/w/

• Place: labial

• Acoustics– /u/-like formant frequencies– Constriction formant values– F1 ~ 330 Hz– F2 ~ 730 Hz– weak F3 (~ 2300 Hz)

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/w/

uh w ae

F1

F2

F3

1000

2000

3000

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/j/

• Place: palatal

• Acoustics– /i/-like formant frequencies– F1 ~ 300 Hz– F2 ~ 2200 Hz– F3 ~ 3000 Hz

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/j/

uh j ae

F1

F2

F3

1000

2000

3000

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/j/

uh j ae

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Liquids (/l/, /r/)

• lateral /l/

• Retroflex /r/

• Pickett (1999) considers these consonants glides as well

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/l/

• Place: alveolar

• Articulatory phonetics:– tongue tip contacts alveolar ridge– Constriction is on each side of this

obstruction – hence the term lateral– Vocal tract is split – not modeled with a

single tube

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/l/

• Acoustics– F1 ~ 360 Hz– F2 ~ 1300 Hz– F3 ~ 2700 Hz– F2 is variable and affected by vowel

environment– Position in word will affect acoustic

features of /l/– Final /l/ will have a higher F1 & lower F2

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/l/

uh l ae

F1

F2

F3

1000

2000

3000

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/l/

uh l ae

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/r/

• Place: palatal

• Articulatory phonetics– /r/ can take on a wide variety of articulator

positions– Tongue can be “bunched” together– Tongue can be “retroflexed”, tipping back

toward the palate– Clearly illustrates that many articulatory

configurations can result in the same acoustic product

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/r/

• Acoustics– Hallmark of /r/ is a low F3– F1 ~ 350 Hz– F2 ~ 1050 Hz– F3 ~ 1550 Hz– Vowels have F3 above 2200 Hz– Vowels around /r/ are colored by it and

exhibit lowered F3 values

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/r/

uh r ae

F1

F2

F3

1000

2000

3000

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“Bunched” /r/

uh r ae

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“Retroflexed” /r/

uh r ae

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A digression…

• /r/ demonstrates that there isn’t a single way to make a speech sound

• /r/ serves to remind us that our source-filter theory allows educated guesses that may not always be right.

• For example, how would you know from acoustics (i.e. formants) if the person is bunching or retroflexing?

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A digression…

• /r/ is a problematic sound for many youngsters to learn

• Why might that be?