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Acoustic and Physiological Phonetics. Vowel Production and Perception. Learning Objectives. Review source-filter theory and how it relates to vowel production Distinguish between source spectrum, transfer function and output spectrum.

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acoustic and physiological phonetics

Acoustic and Physiological Phonetics

Vowel Production and Perception

Stephen M. Tasko

learning objectives
Learning Objectives
  • Review source-filter theory and how it relates to vowel production
  • Distinguish between source spectrum, transfer function and output spectrum.
  • Calculate formant/resonant frequencies of a uniform tube based on its physical dimensions.
  • Describe how the area function of an acoustic resonator is determined.
  • Distinguish between and describe relation between area function and transfer function.

Stephen M. Tasko

source filter theory
Source Filter Theory

Speech

(What We Hear)

Filter

(Resonator)

Source

(Phonation)

Frequency Response

Curve

(Transfer Function)

Input Spectrum

Output Spectrum

Stephen M. Tasko

frequency response curve transfer function
FRC peaks – resonant or formant frequency

Tube resonators have an infinite number of formants

F1, F2, F3 … denotes formants from low to high frequency

Frequency response curve/Transfer Function

F1

F2

F3

F4

Stephen M. Tasko

vocal tract as a tube
Vocal tract as a tube
  • Tubes have physical characteristics (shapes)
  • Tubes act as acoustic resonators
  • Acoustic resonators have frequency response curves (FRC), also known as ‘transfer functions’
  • Tube shape dictates the frequency response curve.

Stephen M. Tasko

the vocal tract shape during vowel production
The vocal tract shape during vowel production
  • Can be (roughly) uniform in shape
    • The vocal tract is fairly uniform in its cross-sectional diameter for neutral or central vowel (schwa)
  • Can also be take on non-uniform shapes
    • Are observed for non-neutral vowels
    • Have a more complex geometry
    • Does not allow simple calculations of formants
    • Formant values are derived from the vocal tract area function

Stephen M. Tasko

vocal tract as a tube1
Vocal tract as a tube

Straight tube, closed at one end,

with a uniform cross-sectional

diameter

Straight tube, closed at one end,

of differing cross-sectional

diameter

Vocal tract: bent tube, closed

at one end, with differing

Cross-sectional diameter.

Stephen M. Tasko

what is an area function
What is an area function?

Area (cm2)

Length along tube (cm)

Stephen M. Tasko

area function of a uniform tube

Area (cm2)

Length along tube (cm)

Area function of a uniform tube
  • Area function dictates the frequency response curve for that tube

Stephen M. Tasko

relationship between vocal tract shape the area function and the frequency response curve
Relationship between vocal tract shape, the area function and the frequency response curve

FRC

Stephen M. Tasko

key points
Key points
  • Vocal Tract has a variable shape, therefore
    • It is a variable resonator
    • Can have a variety of area functions
    • Can generate a variety of frequency response curves
  • A given area function can lead to one (and only one) frequency response curve
  • A given frequency response curve and arise due to a variety of different area functions

Stephen M. Tasko

learning objectives1
Learning Objectives
  • Describe the basic shape of the area function for the four corner vowels.
  • Describe F1-F2 relations for English vowels with specific emphasis of the corner vowels
  • Draw and recognize (1) wide band spectrograms, (2) spectrum envelopes, and (3) frequency response curves for the corner vowels
  • Draw and interpret various plots that relate formants values for English vowels.
  • Outline our basic tongue and lip rules for predicting formant shifts from the neutral position.

Stephen M. Tasko

vowels articulatory description1
Vowels: Articulatory Description
  • Degree of lip rounding
    • Rounded
    • Unrounded
  • Degree of tension
    • Tense
    • Lax

Stephen M. Tasko

neutral configuration
“Neutral” Configuration

Vocal Tract Area Function

Articulatory Configuration/ Vocal Tract Shape

Frequency Response Curve

Stephen M. Tasko

low back vowel
Low back vowel

Vocal Tract Area Function

Articulatory Configuration/ Vocal Tract Shape

Frequency Response Curve

Stephen M. Tasko

high back rounded vowel
High back rounded vowel

Vocal Tract Area Function

Articulatory Configuration/ Vocal Tract Shape

Frequency Response Curve

Stephen M. Tasko

low front vowel
Low front vowel

Vocal Tract Area Function

Articulatory Configuration/ Vocal Tract Shape

Frequency Response Curve

Stephen M. Tasko

relationship between vocal tract shape the area function and the frequency response curve1
Relationship between vocal tract shape, the area function and the frequency response curve

Vocal Tract Area Function

Articulatory Configuration/ Vocal Tract Shape

Frequency Response Curve

Stephen M. Tasko

what distinguishes vowels in production and perception
Resonant (formant) Frequency

F1, F2 frequency are particularly important

F3 frequency plays a smaller role

Landmark study:

Peterson and Barney (1952)

What distinguishes vowels in production and perception?

Stephen M. Tasko

vowels frequency response curve patterns
Vowels: Frequency Response Curve Patterns

Mid Central vowel

F1: 500 Hz

F2: 1500 Hz

/i/

Gain

/u/

//

//

Stephen M. Tasko

frequency

observations
/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 advancement ~ F2

Tongue front F2 

Tongue back F2 

Observations

Stephen M. Tasko

learning objectives2
Learning Objectives
  • Outline the key assumptions and parameters of the Stevens & House (SH) articulatory model of vowel production.
  • Describe the acoustic consequences of changing SH model parameters.
  • Provide acoustic explanations for how (1) the SH model parameters influence area function and (2) how these area function changes influence acoustic (i.e. formant values)
  • Compare the shape of the vowel quadrilateral and the F1-F2 plot

Stephen M. Tasko

connecting the dots

“Connecting the dots”

How do articulatory processes “map” onto acoustic processes?

Stephen M. Tasko

3 parameter model stevens house 1955
Model assumes

No coupling with

Nasal cavity

trachea & pulmonary system

3-parameter model (Stevens & House, 1955)

Stephen M. Tasko

3 parameter model stevens house 19551
Model parameters

Distance of major constriction from glottis (d0)

Radius of major constriction (r0)

Area (A) and length (l) of lip constriction

A/l conductivity index

3-parameter model (Stevens & House, 1955)

Stephen M. Tasko

key goal of study
Key Goal of Study
  • Evaluate the effect of systematically changing each of these three “vocal tract” parameters on F1-F3 frequency

Stephen M. Tasko

general observations
General Observations

Stephen M. Tasko

general observations1
General Observations

Stephen M. Tasko

general observations2
General Observations

Stephen M. Tasko

interpretation double helmholtz resonator model
Interpretation: Double Helmholtz Resonator Model

Back Cavity Volume influences F1

Larger volume = lower F1

Smaller volume=higher F1

Front Cavity Volume influence F2

Larger volume= lower F2

Smaller volume=higher F2

Radius of Conduit (r0) influences F1

Larger radius = higher F1

Smaller radius=smaller F1

Back Cavity

Front

Cavity

Major

Constriction (ro)

Stephen M. Tasko

interpretations
∆ d0 = ∆Vfront & Vback

↑ d0 =↓ Vfront = ↑F2

↑ d0 =↑Vback = ↓ F1

Interpretations

Stephen M. Tasko

interpretations1
↓ r0 =↓ F1

↑ r0 =↑F1

When d0 ↑(anterior)

↓ r0 =↓ Vfront= ↑F2

Interpretations

↑lip rounding

= ↓A/l

= ↓ F1 & F2

Stephen M. Tasko

another way to look at the data
Another way to look at the data

(Minifie, 1974)

Stephen M. Tasko

articulatory acoustic comparisons
Articulatory Acoustic Comparisons

F1-F2 Plot adjusted to reflect

‘articulatory’ space

Traditional F1-F2 Plot

+

d0

-

r0

+

-

Stephen M. Tasko

learning objectives3
Learning Objectives
  • Provide an explanation for why we treat women’s, men’s and children’s vowels as equivalent even though absolute values of formants differ a lot.

Stephen M. Tasko

clinical example
Clinical Example

Stephen M. Tasko

acoustic variables related to the perception of vowel quality
Acoustic variables related to the perception of vowel quality
  • F1 and F2
  • Other formants (i.e. F3)
  • Fundamental frequency (F0)
  • Duration
  • Spectral dynamics
    • i.e. formant change over time

Stephen M. Tasko

how helpful is f1 f2
How helpful is F1 & F2?

From Hillenbrand & Gayvert (1993)

Stephen M. Tasko

how does adding more variables improve pattern classifier success
How does adding more variables improve pattern classifier success?
  • F1, F2 + F3
    • 80-85 %
  • F1, F2 + F0
    • 80-85 %
  • F1, F2 + F3 + F0
    • 89-90 %

Stephen M. Tasko

what about duration
What about Duration?

Stephen M. Tasko

slide51

What about Duration?

Some examples

Stephen M. Tasko

what about formant variation2
What about formant variation?

Naturally spoken/hAd/

Synthesized, preserving original formant contours

Synthesized with flattened formants

Stephen M. Tasko

what about formant variation3
What about formant variation?

Conclusion: Spectral change patterns do matter.

Stephen M. Tasko

what do we conclude
What do we conclude?

Stephen M. Tasko

slide57

Sinewave Speech Demonstration

Sinewave speech examples (from HINT sentence intelligibility test):

Stephen M. Tasko

selected issues that are not resolved
Selected issues that are not resolved
  • What do listener’s use?
    • Specific formants vs. spectrum envelope
  • What is the “planning space” used by speakers?
    • Articulatory
    • Acoustic
    • Auditory

Stephen M. Tasko

the important role of movement
The important role of movement
  • Articulatory movement = spectral change
  • Spectral change occurs as speakers transition within and between sound sequences
  • Spectral change plays a significant role in
    • Perception of certain speech sounds
    • Overall speech intelligibility

Stephen M. Tasko

diphthongs
Diphthongs
  • Slow gliding (~ 350 msec) between two vowel qualities

Components

  • Onglide- starting point of articulation
  • Offglide-end point of articulation
  • Articulatory Transition = formant transition
  • Diphthongization: articulatory movement within the vowel
  • Varies by geographic region

Stephen M. Tasko

american english diphthongs
American English Diphthongs
  • // - “bye”
  • // - “bough”
  • // - “boy”
  • // - “bay”
  • // - “bow”

Stephen M. Tasko