1. Acoustic and Physiological Phonetics
Vowel Production and Perception
Stephen M. Tasko

2. 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

3. Source Filter Theory Speech (What We Hear) Source (Phonation) Filter
(Resonator)
Frequency Response
Curve
(Transfer Function)
Input Spectrum
Output Spectrum
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4. Same Source, Different Filter
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5. 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 F1 F2 F3 F4
Stephen M. Tasko

6. 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

7. 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

8. 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

9. What is an area function?…
Area (cm2)
Length along tube (cm)
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10. Area function of a uniform tube
Area function dictates the frequency response curve for that tube
Area (cm2)
Length along tube (cm)
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11. Vocal Tract Area Function
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12. Vocal Tract Area Function
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13. Relationship between vocal tract shape, the area function and the frequency response curve
FRC
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14. 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

15. 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.
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16. Vowels: Articulatory Description
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17. Vowels: Articulatory Description
Degree of lip rounding
Rounded
Unrounded
Degree of tension
Tense
Lax
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18. “Neutral” Configuration
Vocal Tract Area Function
Articulatory Configuration/ Vocal Tract Shape
Frequency Response Curve
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19. Low back vowel Stephen M. Tasko Vocal Tract Area Function
Articulatory Configuration/ Vocal Tract Shape
Frequency Response Curve
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20. High back rounded vowel
Vocal Tract Area Function
Articulatory Configuration/ Vocal Tract Shape
Frequency Response Curve
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21. Low front vowel Stephen M. Tasko Vocal Tract Area Function
Articulatory Configuration/ Vocal Tract Shape
Frequency Response Curve
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22. 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
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23. 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)
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24. Vowels: Spectrographic Patterns
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25. Vowels: Frequency Response Curve Patterns
Mid Central vowel
F1: 500 Hz
F2: 1500 Hz
/i/
Gain
/u/
//
//
Stephen M. Tasko

26. 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 
Stephen M. Tasko

27. 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
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28. How do articulatory processes “map” onto acoustic processes?
“Connecting the dots”
How do articulatory processes “map” onto acoustic processes?
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29. 3-parameter model (Stevens & House, 1955)
Model assumes
No coupling with
Nasal cavity
trachea & pulmonary system
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30. 3-parameter model (Stevens & House, 1955)
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
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31. 3-parameter model (Stevens & House, 1955)
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32. Key Goal of Study
Evaluate the effect of systematically changing each of these three “vocal tract” parameters on F1-F3 frequency
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33. General Observations
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34. General Observations
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35. General Observations
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36. 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)
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37. Interpretations ∆ d0 = ∆ Vfront & Vback ↑ d0 = ↓ Vfront = ↑ F2
↑ d0 = ↑ Vback = ↓ F1
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38. Interpretations ↓ r0 = ↓ F1 ↑ r0 = ↑ F1 ↑ lip rounding = ↓ A/l
When d0 ↑ (anterior)
↓ r0 = ↓ Vfront = ↑ F2
↑ lip rounding
= ↓ A/l
= ↓ F1 & F2
Stephen M. Tasko

39. Another way to look at the data
(Minifie, 1974)
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40. Articulatory Acoustic Comparisons
Traditional F1-F2 Plot
F1-F2 Plot adjusted to reflect
‘articulatory’ space r0 d0 - +
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41. 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.
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42. Stephen M. Tasko

43. “normalizing” formant values
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44. Clinical Example
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45. 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

46. How helpful is F1 & F2? Data Source Human Listeners Pattern Classifier
Peterson & Barney (1952)
94.4 %
74.9 %
Hillenbrand et al. (1995)
95.2 %
68.2 %
From Hillenbrand & Gayvert (1993)
Stephen M. Tasko

47. How does adding more variables improve pattern classifier success?
F1, F2 + F3
80-85 %
F1, F2 + F0
F1, F2 + F3 + F0
89-90 %
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48. Nearby vowels have different durations
How about Duration?
Nearby vowels have different durations
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49. Stephen M. Tasko

50. What about Duration?
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51. What about Duration?
Some examples
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52. What about formant variation?
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53. What about formant variation?
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54. What about formant variation?
Naturally spoken /hAd/
Synthesized, preserving original formant contours
Synthesized with flattened formants
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55. What about formant variation?
Conclusion: Spectral change patterns do matter.
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56. What do we conclude?
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57. Sinewave Speech Demonstration
Sinewave speech examples (from HINT sentence intelligibility test):
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58. 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

59. 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

60. 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

61. American English Diphthongs
// - “bye”
// - “bough”
// - “boy”
// - “bay”
// - “bow”
Stephen M. Tasko